Table 517.1 A Hospital Emergency System Must Serve These Loads (Sec. 517.31)
517.34. Equipment System Connection to Alternate Power Source. This is where the equipment system comes in, comprised primarily of three-phase power loads. Ventilation systems for operating and delivery rooms were added under delayed automatic connection for the 2008 NEC.
517.41. Essential Electrical Systems. This section covers nursing homes and limited care facilities. In part (B), a single transfer switch may be used for the entire essential electrical system instead of using a separate transfer switch for each branch. One transfer switch may supply one or more branches of the essential electrical system in a nursing home or residential custodial care facility where the essential electrical system has a maximum demand of 150 kVA. This also raises the conflict between this article and 700.6(D), as discussed previously. Separate transfer switches are required only if dictated by load considerations. For small facilities, the essential electrical system generally consists of the life safety branch and the critical branch. For larger systems, the critical branch is divided into three separate branches for patients, heating, and sump pumps and alarms. Code diagrams 517.41 Nos. 1 and 2 illustrate typical installations.
517.42. Automatic Connection to Life Safety Branch. Part (A) describes the switching arrangements for night transfer of corridor lighting. The rule is intended to ensure that some lighting will always be provided in the corridor regardless of the mode of operation.
517.43. Connection to Critical Branch. This section details the loads requiring transfer from normal source to the alternate power source. In part (B)(2), elevator operation must not trap passengers between floors. This is now mandatory.
517.45. Essential Electrical Systems for Other Health Care Facilities. This section is increasingly important as health care decentralizes. If these facilities have critical care areas or patients on life support, then an essential electrical system as covered in 517.30 through 517.35 will be applied, or a battery system is permitted.
517.60. Anesthetizing Location Classification. The rules for flammable anesthetizing locations in the NEC are virtually obsolete. No hospital in the United States is using or has used ether and other such agents for many years. However, the rules have not been removed from the NEC because the NEC is used in other countries, and some of them are still using flammable anesthetics. Figure 517-6 shows the classified hazardous locations of part (A).
Fig. 517-6. Two types of hazardous locations must be identified. (Sec. 517.60.)
Note that part (B) requires designation by the hospital administration that a particular location (operating room, anesthesia room, etc.) is nonhazardous. Common sense as well as other NFPA standards would dictate signs prohibiting the use of flammable anesthetics.
Hazardous locations rules are separated from those for other-than-hazardous locations. A third category is also designated: “above-hazardous locations.” The Code covers wiring and equipment in three relations to anesthetizing locations: 517.61(A), within-hazardous; 517.61(B), above-hazardous; and 517.61(C), other-than-hazardous.
517.61. Wiring and Equipment. Part (A) calls for explosionproof wiring methods, in general, for such locations.
Part (A)(4) notes an extension of the hazardous boundary. 517.60(A)(1) defines the area of a flammable anesthetizing location as a Class I, Division 1 location from the floor to a point 5 ft (1.5 m) above the floor. The question then arises, “Is the seal required in the upper conduit entering the switch box on the wall of a hospital operating room as shown in Fig. 517-7?” The box is partly below and partly above the 5-ft (1.5-m) level.
Fig. 517-7. Boundary of Class I, Division 1 location may be extended. (Sec. 517.61.)
Part (A)(4) states that if a box or fitting is partially, but not entirely, beneath the 5-ft (1.5-m) level, the boundary of the Class I, Division 1 area is considered to extend to the top of the box or fitting. Therefore, the box or fitting is entirely within the hazardous area, and a seal is required in conduit entering the enclosure from either above or below, as shown in Fig. 517-7.
If the box or fitting is entirely above the 5-ft (1.5-m) level, a seal would not be required at the box or fitting, but conduit running to the box from the hazardous area would have to be sealed at the boundary, on the hazardous-location side of the box. If the box shown were recessed in the wall instead of surface-mounted, some means would have to be provided to make the seals accessible [501.15(C)(1)], such as removable blank covers at the locations of the seals.
Part (A)(5) calls for explosionproof receptacles and plugs within hazardous locations described in 517.60(A).
In part (B)(1) of this section, rigid metal conduit, electrical metallic tubing (EMT), and intermediate metal conduit (IMC) or Type MI or MC cable that has a continuous “gas/vaportight” sheath are permitted in “above-hazardous anesthetizing locations.” In “other-than-hazardous anesthetizing locations” [517.61(C)(1)], wiring may be in a metal raceway or cable assembly, but the cable armor must qualify as a ground return path per 250.118.
The NE Code generally requires that “hospital-grade” receptacles (the UL-listed green-dot wiring devices) be used at patient bed locations in health care facilities. However, note that 517.61(B)(5) and 517.61(C)(2) of the Code also require use of “receptacles and attachment plugs” that are “listed for hospital use” above “hazardous” anesthetizing locations and in “other-than-hazardous” anesthetizing locations. As described, these rules require that all 2-pole, 3-wire grounding-type receptacles and plugs for single-phase 120-, 208-, or 240-V AC service must be marked “Hospital Only” or “Hospital Grade” and have a green dot on the face of each receptacle (Fig. 517-8). The relation between the phrase “listed for hospital use” and the phrase “Hospital Grade” is explained in the UL Electrical Construction Materials Directory (Green Book), under the heading “Attachment Plug Receptacles and Plugs.” It says:
Fig. 517-8. Hospital-grade plugs and receptacles are required for anesthetizing locations. (Sec. 517.61.)
Receptacles for hospital use in other than hazardous (classified) locations in accordance with Art. 517 of the NEC are identified (1) by the marking “Hospital Only” (used to identify a specific grounding locking configuration rated 20 A, 125 V used for the connection of mobile x-ray and similar equipment) or (2) by the marking “Hospital Grade” and a green dot on the face of the receptacle. The identification is visible during installation on the wiring system or, in the case of the appliance outlet, after installation on the utilization equipment.
Of course, in the defined hazardous areas of flammable anesthetizing locations [517.60 and 517.61(A)(5)], receptacles must be explosionproof type, listed for Class I, Division 1 areas.
Underwriters’ Laboratories devised a special series of tests for wiring devices intended for hospital use. These tests are substantially more abusive than those performed on general-purpose devices and are designed to ensure the reliability of the grounding connection in particular, when used in the hospital environment. Hospital-grade receptacles have stability and construction in excess of standard specifications and can stand up to abuse and hard use. Devices that pass this test are listed as “Hospital Grade” and are identified with these words and a green dot, both of which are visible after installation. UL listings include 15- and 20-A, 125-V grounding, nonlocking-type plugs, receptacles, and connectors. This class of device is acceptable for use in any nonhazardous anesthetizing location (Fig. 517-9). As noted in the exception to 517.61B)(2), receptacles above a hazardous location do not have to be totally enclosed and may be standard, available hospital-grade receptacles of the type that would be used to satisfy the rule of 517.61(B)(5).
Fig. 517-9. Although the NE Code requires use of hospital-grade receptacles at patient bed locations and in “anesthetizing” locations, the ruggedness and high degree of connection reliability strongly recommend their use for such critical applications as plug-connection of respiratory or life-sustaining equipment.
As covered in part (C)(1), in anesthetizing locations that are not hazardous (no flammable agents used), Type AC cable is recognized along with Types MI and MC cable and rigid metal conduit, IMC, and EMT—but any such cable or raceway must contain an insulated-copper equipment grounding conductor and its outer jacket must be an approved grounding conductor. Note that, although the rule here does not specify a copper conductor, because an anesthetizing location is a patient care area, the copper wire is required by 517.13.
517.63. Grounded Power Systems in Anesthetizing Locations. Part (A) used to call for a general-purpose lighting circuit, fed from the normal grounded service, to be installed in each operating room. And an exception used to recognize feed from an emergency generator or other emergency service that is separate from the source of the hospital’s “Emergency System,” as defined in 517.2. Figure 517-10 shows a layout where such an emergency supply (at lower right) is now the required source of supply to the lighting circuit in the operating room. Now, emergency illumination is required to be supplemented by at least one battery-powered emergency luminaire.
Fig. 517-10. General-purpose lighting circuits may be fed from the normal service, or from a separate alternate source. [Sec. 517.63(C).]
In part (F), an isolated power system (ungrounded operation with a line isolation monitor) is required only in an anesthetizing location with flammable anesthetics. Long ago, isolated power systems were required for locations with both flammable and non-flammable anesthetics. But in 1984, a revision was made in the former 517-104(A)(1) to change the phrase “anesthetizing” to “flammable anesthetizing” in this section. As a result, anesthetizing location that do not use flammable anesthetics (and as noted none do) don’t require use of an isolated power system. 517.63(F) now makes the requirement for an isolated power system applicable only for anesthetizing locations where “flammable” anesthetics are used. For those cases where the anesthetizing location is used solely for nonflammable anesthetizing materials, an isolated power system is not mandatory in the NEC [although NFPA 99 and 517.20(B) for some wet procedure areas still require it under some circumstances]. It is also used by design in many facilities.
Figure 517-11 shows the application of a completely packaged transformer loadcenter to provide power for the ungrounded, isolated circuits in hospital operating suites.
Fig. 517-11. Isolated power supply is required for circuits only in flammable anesthetizing locations. (Sec. 517.63.)
517.64. Low-Voltage Equipment and Instruments. Specific details are given for use of low-voltage equipment in an anesthetizing location. Figure 517-12 shows some of the rules. 517.160(A)(2) limits isolating transformers to operation with primary at not over 600 V.
517.160. Isolated Power Systems. Each isolated power circuit must be controlled by a switch that has a disconnecting pole in each isolated circuit conductor to simultaneously disconnect all power. That is in part (A)(1).
As covered in part (A)(2), any transformer used to obtain the ungrounded circuits must have its primary rated for not more than 600 V between conductors and must have proper overcurrent protection. This Code rule used to limit the transformer primary to 300 V between conductors, which often required two stages of voltage transformation to comply with the rule, as shown in Fig. 517-13. This diagram shows the circuit makeup used in a hospital to derive the 120-V ungrounded circuits, with transformation down from 480 to 240 V and then to 120 V. The ungrounded secondary system must be equipped with an approved ground contact indicator, to give a visual and audible warning if a ground fault develops in the ungrounded system.
Fig. 517-12. Low-voltage circuits in anesthetizing locations must operate at 10 V or less or be otherwise approved. (Sec. 517.64.)
Fig. 517-13. Two-stage transformation was often needed for isolated circuits but is no longer necessary. (Sec. 517.160.)
Isolating transformers must be installed out of the hazardous area [part (A)(3)]. The ground indicator and its signals must also be installed out of the hazardous area. In an anesthetizing location, the hazardous area extends to a height of 5 ft (1.5 m) above the floor.
Fixed lighting fixtures above the hazardous area in an anesthetizing location, other than the surgical luminaire, and certain x-ray equipment may be supplied by conventional grounded branch circuits [517.63(B) and 517.63(C)].
Part (A)(5) requires isolated circuit conductors to be identified by brown and orange colors. Each wire must be striped with some color other than white, gray, or green so it will not be confused, for example, with the high leg on a center-tapped delta system. Although these systems are ungrounded and therefore by definition have no grounded circuit conductors, there is still a standard protocol as to which color to use when connecting to the “white” side of a conventional 125 V receptacle. Use the striped orange wire for this side of the receptacle.
Part (B)(1) details a line isolation monitor and clarifies line isolation monitor alarm values, specifying 5.0 mA as the lower limit of alarm for total hazard current. Figure 517-14 shows the basic concept behind detection and signal of a ground fault. The diagram shows major circuit components of a typical ground detector/alarm system. Partial ground energizes current-relay A, opening contact A2 (energizing red light and warning buzzer). Pressing the momentary-contact silencer switch energizes coil C, opening contact C1 (disconnecting buzzer), and closing holding contact C2. When ground is cleared, contacts resume the position shown in Fig. 517-14.
Fig. 517-14. Detection and alarm on ground fault is required for isolated power systems. (Sec. 517.160.)
The purpose of such a ground indicator is to provide warning of the danger of shock hazard and the possibility of a fault in the system due to accidental grounding of more than one conductor. If one conductor of an isolated system becomes grounded at one point, normal protective devices (fuses or CBs) will not operate because there is no return path and, therefore, no flow of short-circuit fault current. However, if an accidental ground subsequently develops on the other conductor, a short circuit will occur, with possible disastrous consequences, such as ignition of ether vapors by arc or a lethal shock to personnel.
518.1. Scope. This article covers places of “assembly,” but does not apply to theaters, which is regulated by Art. 520. It covers any single indoor space (a whole building or part of a building) designed or intended for use by 100 or more persons for assembly purposes. That includes dining rooms, meeting rooms, entertainment areas (other than with a stage or platform or projection booth), lecture halls, bowling alleys, places of worship, dance halls, exhibition halls, museums, gymnasiums, armories, group rooms, funeral parlor chapels, skating rinks, pool rooms, transportation terminals, court rooms, sports arenas, and stadiums. A school classroom for less than 100 persons is not subject to this article. See 518.2. A supermarket with a rated occupancy load over 100 persons is not subject to this article because there is no assembly purpose and no likelihood of self-reinforcing panic during an emergency, as contrasted with the same number of people in an auditorium.
The clear differentiation given in this section points out that any such building or structure or part of a building that contains a projection booth or stage platform or even just an area that may, on occasion, be used for presenting theatrical or musical productions—whether the stage or platform is fixed or portable—must comply with the rules of Art. 520, as if it were a theater, and not Art. 518. A restaurant, say, that has a piano player for entertainment on Saturday night, could readily be classed as a theater and subject to Art. 520. This is covered in 518.2(C).
Article 518 directs attention “to a building or portion of a building” that would be used for the purposes outlined; therefore, you would have to determine how the occupancy is used.
A supermarket generally would not have a public assembly area. However, a department store could incorporate a community room for shows and similar audience functions. This room would be subject to Art. 518. The main areas of supermarkets and department stores, unlike theaters and assembly halls, have many aisles and exits that could be used in case of emergency evacuation of the building. It is these characteristics that permit conventional wiring methods to be accepted.
A proposal was once made to include supermarkets and department stores as “places of assembly,” but it was rejected.
Note that places of assembly covered by this article must be for 100 or more people. As a practical matter, questions of occupancy load belong with the local building official.
518.4. Wiring Methods. The basic rule says that fixed wiring must be in a metal raceway, flex metal conduit, and nonmetallic raceways encased in not less than 2 in. (50 mm) of concrete, Type MI, MC or AC cable. Part (B) says that non-metallic-sheathed cable, BX (Type AC cable), electrical nonmetallic tubing (ENT), and rigid nonmetallic conduit may be used in building areas that are not required by the local building code to be of fire-rated construction. Note that use of these methods no longer relates to the number of persons that the place holds, which was once in this rule. Another exception permits the use of other wiring methods for sound systems, communication circuits, Class II and III remote-control and signal circuits, and fire-alarm circuits.
Another allowance gives limited permission to use ENT and rigid PVC (and RTRC) conduits in smaller conference and meeting rooms in restaurants and in a variety of similar occupancies, provided the nonmetallic wiring is behind a thermal barrier providing at least 15 min of fire separation, such as conventional ½-in. drywall. It is also permitted above a suspended ceiling assembled in compliance with a recognized fire rating protocol. Of course, if the suspended ceiling is air-handling, 300.22(C) would not allow such wiring methods within the plenum cavity ceiling.
520.1. Scope. Where only a part of a building is used as a theater or similar location, these special requirements apply only to that part and do not necessarily apply to the entire building. A common example is a school building in which there is an auditorium used for dramatic or other performances. All special requirements of this chapter would apply to the auditorium, stage, dressing rooms, and main corridors leading to the auditorium but not to other parts of the building that do not pertain to the use of the auditorium for performances or entertainment.
520.2. Definitions. These are the specialized terms used in this article. Of note for the 2008 NEC is the new term (and technology) “Solid-State Sine Wave Dimmer.” This equipment produces current that varies with voltage over time, so both the current and voltage traces are in step. These dimmers do not draw harmonic currents from the neutral and the feeders and branch circuits they feed do not need to consider their neutrals to be loaded due to harmonic, nonlinear currents. They are also recognized in 518.5 for assembly areas.
520.5. Wiring Methods. Building laws usually require theaters and motion picture houses to be of fireproof construction; hence, practical considerations limit the types of concealed wiring for light and power chiefly to metal race-ways. Only Type MI or MC cables may be used, or Type AC with an insulated equipment grounding conductor. Cables were long ago found unsuitable for circuits in theaters because they do not readily offer increase in the size of conductors for load growth. Many instances of overfusing dictated the value of raceways, which do permit replacement of larger conductors for safely handling load growth. Other wiring methods are permitted in areas for which the local building code does not require fire rating.
Much of the stage lighting in a modern theater is provided by floodlights and projectors mounted in the ceiling or on the balcony front. In order that the projectors may be adjustable in position, they may be connected by plugs and short cords to suitable receptacles or “pockets.”
There is an exception to the basic rule. Recording, communications, remote-control signaling, and fire alarm circuits may be installed using other wiring methods. And those installations described in parts (B) and (C) may also use other wiring methods.
520.6. Number of Conductors in Raceway. This rule is important because it removes the 30 conductor ceiling for waiving the mutual conductor heating limitations of 310.15(B)(2)(a). Therefore larger numbers of conductors can run within wireways and auxiliary gutters without a derating penalty. This arrangement is very advantageous for the large numbers of conductors, supplied by many different dimmers, that supply stage lighting that goes on and off as the lighting needs of a production change.
520.9. Branch Circuits. This section includes other important Chap. 5 modifications of Chap. 1 through 4 rules (see 90.3), this one specifically waiving the 80 percent current limitation for receptacle loading on circuits with multiple receptacles or outlets that normally applies. For example, each receptacle in a 20 A duplex receptacle or comprising multiple single 20 A receptacles on a 20 A circuit must not be loaded over 16 A under normal circumstances, but for theatrical applications every receptacle could be loaded up to the full 20 A as long as the receptacle rating was fully equal to the size of the overcurrent device. These receptacles typically operate for short loading periods that would not cause nuisance tripping of the overcurrent protection. It should be noted that the usual plugs and receptacles for this purpose are not of the usual NEMA configuration, but rather a linear arrangement of three unevenly spaced pins and sleeves for which the spacing polarizes the device.
The express permission in the first sentence “of any size” allows a receptacle circuit to supply stage lighting equipment of large current ratings even if it exceeds the 40- and 50-A limitations for lighting connections in 210.23. Normally, however, the loading will be subdivided through branch-circuit overcurrent devices that are lower than those sizes. Note also that 520.41(B) does not waive the enhanced lampholder requirements in 210.23 that apply to circuits rated above 20 A.
520.10. Portable Equipment. Portable stage equipment is permitted outdoors on a temporary basis, provided it is appropriately supervised and the general public is excluded from access.
520.23. Control and Overcurrent Protection of Receptacle Circuits. The term auditorium receptacles should be understood as including all receptacles, wherever they may be located, that are intended for the connection of stage lighting equipment. Circuits to such receptacles must of necessity be controlled at the same location as other stage lighting circuits.
520.24. Metal Hood. Because of the large amount of flammable material always present on a stage, and because of the crowded space, a stage switchboard must have no live parts on the front, and the back must be so guarded as to keep unauthorized persons away from the space in back of the board and the wall, with a door at one end of the enclosure. This is archaic construction; today’s switchboards are metal-enclosed with dead fronts as required in 520.21. The rule exists to cover existing equipment that may not be entirely enclosed.
The more important stage switchboards are commonly of the remote-control type. Pilot switches mounted on the stage board control the operation of contactors installed in any convenient location where space is available, usually below the stage. The contactors in turn control the lighting circuits.
The stage switchboard is usually built into a recess in the proscenium wall, as shown in the plan view, Fig. 520-1. After passing through the switches and dimmers, many of the main circuits must be subdivided into branch circuits so that no branch circuit will be loaded to more than 20 A. Where the board is of the remote-control type, the branch-circuit fuses are often mounted on the same panels as the contactors. Where a direct-control type of board is used, and sometimes where the board is remotely controlled, the branch-circuit fuses are mounted on special panelboards known as magazine panels, which are installed in the space in back of the switchboard, usually in the location of the junction box shown in Fig. 520-2.
Fig. 520-1. Stage switchboards must be circuited to provide highly flexible usage. (Sec. 520.24.)
Fig. 520-2. Branch circuits of lighting may be controlled by single dimmer in grounded or ungrounded conductor. (Sec. 520.25.)
520.25. Dimmers. Figure 520-2 shows typical connections of two branch circuits arranged for control by one switch and one dimmer plate or section. The single-pole switch on the stage switchboard is connected to one of the outside buses, and from this switch a wire runs to a short bus on the magazine panel. The magazine panel is similar to an ordinary panelboard, except that it contains no switches and the circuits are divided into many sections, each section having its own separate buses. One terminal of the dimmer plate, or variable resistor, is connected to the neutral bus at the switchboard, and from the other terminal of the dimmer a wire runs to the neutral bus on the magazine panel. This neutral bus must be well-insulated from ground and must be separate from other neutral buses on the panel; otherwise, the dimmer would be shunted and would fail to control the brightness of the lamps.
While the dimmer is permanently connected to the neutral of the wiring system, this neutral is presumed to be thoroughly grounded and, hence, the dimmer is dead. A dimmer in the grounded neutral does not require overcurrent protection, as noted in part (A).
Figure 520-3 shows an autotransformer used as a dimmer. By changing the position of the movable contact, any desired voltage may be supplied to the lamps, from full-line voltage to a voltage so low that the lamps are “black-out.” As compared with a resistance-type dimmer, a dimmer of this type has the advantages that it operates at a much higher efficiency, generates very little heat, and, within its maximum rating, the dimming effect is not dependent on the wattage of the load it controls. These dimmers are seldom used today; contemporary dimming systems are digitally controlled.
Modern dimming systems use digital controls to control multiple dimmer racks with dozens of dimmers per rack and where necessary, multiple racks bused together with total capacities measured in hundreds of kilowatts. Each dimmer typically controls a single 20 A circuit.
Fig. 520-3. Autotransformer dimmer must have grounded leg common to primary and secondary. (Sec. 520.25.)
520.27. Stage Switchboard Feeders. Part (A)(2) of this section covers the supply of patch panels, formally referred to in the NEC as intermediate stage switchboards. They receive power from dimmer banks operating at various voltage levels and distribute it out over the various available branch circuits as selected, allowing sets of luminaires to operate at one of the available dimmer settings in the main stage switchboard. For this reason there will be a number of feeders, one for each dimmer setting. In addition, there will be a common neutral return sized to the maximum unbalanced load, but it need not be larger than the primary stage switchboard neutral. If run in the form of parallel conductors, the usual rules for parallel conductors apply, including the obligation to represent the neutral in all parallel raceways, to use wires no smaller than 1/0 AWG, and to divide the load on the associated ungrounded conductors as equally as possible. The common neutral means that the originating switchboard must be fed with a single feeder.
As digital controls take over this industry, patch panels are becoming obsolete. Instead, the power is increasingly distributed from the primary stage switchboard, avoiding the intermediate layer in the distribution altogether. Since literally hundreds of dimmers can be located at a convenient location, and since they can be addressed electronically with multiprocessor support and controlled individually with ease, this is the direction the theater industry is moving. These dimmer racks (switchboards) can be fed with a single feeder as in (A)(1), or if of large size, fed with multiple feeders as in (A)(3). In this case the switchboard must be prominently labeled with the disconnect location(s) and the number at each applicable location. Further, if the disconnects are from multiple switchboards, then the primary switchboards must include barriers to subdivide it in a manner that corresponds to the number of ungrouped remote disconnects that comprise its source of supply.
Part (B) used to require that all neutrals supplying these switchboards be counted as current-carrying conductors due to the harmonic loading produced by contemporary dimming systems. However, the advent of the new “solid-state sine wave 3-phase 4-wire dimming systems” made it possible for the 2008 NEC to waive this requirement, but only where the dimming is exclusively provided from such sources. If conventional dimming sources are used, in whole or even in part, then the neutrals must be counted as current carrying.
Part (C), which first entered the 1993 NEC, clarifies that switchboard feeders are permitted to be sized based on the maximum anticipated load, and not necessarily on the basis of every last watt that the dimmers can put out. There were many documented examples of inspection authorities making that insistence, which was completely unrealistic. To use this allowance the feeder must be protected at its ampacity (next higher standard size not allowed) and any egress or emergency lighting must be divorced from this feeder so it will be unaffected in the event it opens.
520.43. Footlights. A footlight of the disappearing type might produce so high a temperature as to be a serious fire hazard if the lamps should be left burning after the footlight is closed. Part (C) calls for automatic disconnect when the lights disappear.
There is no restriction on the number of lamps that may be supplied by one branch circuit. The lamp wattage supplied by one circuit should be such that the current will be slightly less than 20 A.
Individual outlets as described in part (B) are seldom used for footlights, as such construction would be much more expensive than the standard trough type.
A modern type of footlight is shown in Fig. 520-4. The wiring is carried in a sheet-iron wire channel in the face of which lamp receptacles are mounted. Each lamp is provided with an individual reflector and glass color screen, or roundel. The circuit wires are usually brought to the wire channel in rigid conduit. In the other type of footlight, still used to some extent, the lamps are placed vertically or nearly so, and an extension of one side of the wire channel is shaped so as to form a reflector to direct the light toward the stage.
Fig. 520-4. Footlights must be automatically de-energized when the flush latch is closed down. (Sec. 520.43.)
520.44. Borders and Proscenium Sidelights. Figure 520-5 is a cross section showing the construction of a border light over the stage. This particular type is intended for the use of 200-W lamps. An individual reflector is provided for each lamp so as to secure the highest possible efficiency of light utilization. A glass roundel is fitted to each reflector; these may be obtained in any desired color, commonly white, red, and blue for three-color equipment and white, red, blue, and amber for four-color equipment. A splice box is provided on top of the housing for enclosing the connections between the border-light cable and the wiring of the border. From this splice box, the wires are carried to the lamp sockets in a trough extending the entire length of the border.
Fig. 520-5. Border lights must comply with NEC construction rules. (Sec. 520.44.)
Border lights are usually hung on steel cables so that their height may be adjusted and so that they may be lowered to the stage for cleaning and replacing lamps and color screens; hence, the circuit conductors supplying the lamps must be carried to the border through a flexible cable. The individual conductors of the cable may be of 14 AWG, though 12 AWG is more commonly used. Note that there is a special ampacity table in the NEC for listed extra-hard usage cord connected to these luminaires.
The table governs the ampacity of extra-hard usage multiconductor cords used for border lights, where they are not in direct contact with equipment containing heat-producing elements. The ampacities in this new table are identical to those in Table 400.5B in Column F (3 current-carrying conductors) for similar cords, however, where Table 400.5B begins at 8 AWG and goes up to 500 kcmil, this table begins at 14 AWG and goes up to 2 AWG. The ampacities below 8 AWG are proportionately reduced, but far higher than those in Table 400.5A which would otherwise apply to the smaller cords.
The table also sets the maximum overcurrent device ratings for each cord, which are identical to the values in Column A of Table 400.5A, that is, the traditionally determined cord ampacities for cord with three current-carrying conductors. These values are far lower that the allowable cord ampacities. For example, 10 AWG 75°C rated cord has an ampacity of 41A and maximum over-current device rating of 25A. These cords often run in areas with comparatively high temperatures, and these restrictions add a safety factor for this as well.
The value of the higher ampacities comes where large numbers of these cables travel together in limited space, resulting in derating penalties. This frequently occurs in these applications. The new table helps here as well, resurrecting the old mutual conductor heating table break points with the 70% bracket applicable for 7-24 conductors, the 60% bracket for 25-42 conductors, and 50% for more. This table now appears in Annex B as Table B-310-11.
These more liberal factors are conditioned on at least 50% load diversity. This is normally the case for the same reasons that allowed the change in calculations for stage switchboard feeders in 520.27(C). Note that load diversity is not defined, but as used in Table B.310.11 it is the ratio of energized conductors to the total number of conductors, which in this case could include grounding conductors. See the discussion in Annex B on this topic for more information. If the current-carrying conductors exceed 50% of the total, then the derating factors in Sec. 400.5 would have to be applied in order to avoid overheating the cables and violating the ultimate insulation temperature restriction at the bottom of the table.
Under typical stage conditions, it should almost always be possible to stay within this table for calculations using extra-hard usage cords in general. The allowances are limited to extra-hard usage cord, which includes the stage cables (SC, SCE, and SCT).
520.49. Smoke Ventilator Control. A normally closed-circuit device has the inherent safety feature that, in case the control circuit is accidentally opened by the blowing of a fuse or in any other way, the device immediately operates to open the flue dampers.
520.50. Road Show Connection Panel (A Type of Patch Panel). This section effectively describes the interface between fixed stage wiring and portable stage switchboards covered in Sec. 520.53. Note that these provisions cover the construction of the connection panel and do not apply to wiring connected thereto. Part (A) requires the point where a circuit is connected to consist of an inlet that matches, by current and voltage, that of the receptacle supplied at the other end of the wiring outlet controlled by the panel. Part (B) requires that when a panel transfers power from the fixed switchboard in the building to that supplied by the portable switchboard, the transfer must include all circuit conductors including the grounded circuit conductor, and the transfer must be simultaneous with respect to all circuit conductors. Part (C) requires supplemental overcurrent protection for the supplied connections. Although this is normally provided in the supply switchboards, there are instances in old theaters where this cannot be relied upon, and the supplementary protection required here is important because as their name implies, these panels do not have a permanent address.
520.51. Supply. This section addresses the actual connection point for portable stage switchboards. These are often referred to as a “bull switch”; see the definition of this term in 530.2 for more information. The literal text calls for “power outlets” with the appropriate voltage and current rating. Be careful here because a “power outlet” in this context however, is not necessarily the equipment covered under this heading in the UL White Book (guide card designation QPYV). Although the UL covered equipment (typically enclosed assemblies incorporating receptacles and fused switches or circuit breakers) is certainly suitable for this application, it seems intended that this section also includes other connection methods including sequential interlocking connections of single conductors as covered in 520.53(K) and even direct connections to busbars, as covered in 520.53(H)(1). Although these latter references expressly cover only the load end of the feeder, the same feeder must have a supply connection. If the only possible connection were to an appropriately rated power outlet, then most of the motivation for special precautions and warning labels in 520.53(P) would disappear.
520.53. Construction and Feeders. This section, one of the longest in the entire NEC, covers the requirements for supplying portable switchboards (dimmer racks) used on stage. This equipment is covered by UL under the category “Power Distribution Equipment, Portable (guide card designator QPRW)”. In part (F), specs cover conductors within portable stage dimmer switchboards. A broad, detailed rule covers the temperature ratings of conductors permitted in dimmer boards, based on the type of dimmer used. The rule recognizes the difference in temperature of dimmers and permits lower-rated conductors for solid-state dimmers. Part (G) requires a pilot light arranged to show the presence of power even if a main switch on the unit is in the open position.
Part (H) covers the specifications for the feeder conductors to these units, which often are on casters to allow for easy repositioning. As such, the feeders must utilize a robust and flexible method of connection, and therefore require listed extra hard usage cord or cable. As in cases covered by 520.27(C), the supply ampacity must equal the load connected to the switchboard, and need not be sized in terms of its maximum capacity.
Par. (2) covers the use of single-conductor cable sets, provided the conductors are not smaller than 2 AWG. Single conductors do not experience mutual conductor heating and therefore have much higher ampacities than multiconductor make-ups. This makes them useful for these applications. For example, the ampacity of 2 AWG 75°C stage cable [from Table 400.5(B)] is 170 A; if 75°C multiconductor cable were used, 520.53(O)(2) would require counting the neutral on conventional dimmers, and therefore (170 A ÷ 0.8 = 213 A) a 3/0 AWG cable would be required. Such a cable weighs in at about 4.5 kg/m (3 lb/ft) and would not be practical for this use.
This paragraph, by specifically recognizing paralleled applications, also modifies 310.4(A) to lower the threshold from 1/0 AWG to 2 AWG for these applications, although the equal length and the equal sizing rules still apply. In support of the principle that mutual conductor heating should not be a factor, the wording specifically prohibits bundling the single conductors, although they are to be grouped. The grounded conductors must be identified with at least 150 mm (6 in.) of marking at each end with white or gray, and the equipment grounding conductor (permitted to be not smaller than 6 AWG and otherwise sized by 250.122) the same way except the color is to be green. The ungrounded conductors must be identified by system if multiple voltage systems are present in the premises wiring.
Par. (3) and (4) address tap rules for portable switchboards. They allow for smaller switchboards to be connected to larger sized power outlets covered in 520.51 without additional overcurrent protection. The feeders must not penetrate structural elements of the building, or run through doors or other traffic areas and must terminate at a single overcurrent device in the portable switchboard. This device must protect the feeder from overload by its size; no next higher standard size allowance applies here. If run as single conductors, the feeder conductors must not be bundled, and the terminations must be approved. Par. (3) covers 3.0 m (10 ft) taps, and in addition to the foregoing the feeder conductor ampacity must be not less than one-quarter of the rating of the supply side protection, and the feeders must be kept off the floor in an approved way. Par. (4) covers 6.0 m (20 ft) taps, which must adhere to the same rules except the protection ratio of one-half is more conservative, and these taps must be elevated not less than 2.1 m (7 ft) above the floor, except at terminations.
Par. (5) allows feeders to pass through holes in a wall if specifically designed for this purpose, and provided the feeder is not using the one of the tap allowances in the prior two paragraphs. The hole must be fire-stopped if a fire rating applies to it. This allows for special shows to run off an outdoor generator that would otherwise overtax the existing stage distribution system in the building.
Part (I) covers common-sense rules for bushing openings through which conductors pass and strain-relieving terminations. If passing through ferrous enclosure walls, the phase and neutral legs of portable switchboard feeders must pass through a common opening to avoid inductive heating.
Part (J) limits mated conductor pairings (as in plugs and connector bodies) for feeders to three per run up to 30 m (100 ft). In the common instance where there is such a connection at each end, the rule would set a minimum cord length of 15 m (50 ft) for at least one set of cords. If the run is longer, one additional interconnection is permitted for every 30 m (100 ft).
Part (K) covers single-pole separable connectors, which include three forms. This rule specifically waives the normal strain relief rule in 400.10, and thereby meets the exception thereto. It also waives the unique configuration and marking rules in 406.6 and 406.7 because such devices are rated in amperes but can be used on may circuit configurations including parallel applications where there will be any of a number of Phase “A” and “B” and “C” and “N” conductors, etc. For parallel applications, there must be a prominent label advising of the internal parallel connections. A compliant installation where these are used must meet at least one of three design criteria. The first is that the connections are interlocked with the source such that the feeder is deenergized until the connections are complete. The second option uses listed sequential interlocking mechanisms to assure appropriate sequencing of connections, with equipment grounding first, neutral second, and phase conductors last, with the reverse order for disconnection. The final option is single connectors with no interlocking mechanism, in which case a label at the line connections must detail the correct connection sequence. Note that any such application must only be serviced by qualified individuals, as covered in 520.53(P).
Part (L) requires protection against physical damage to these conductors. For example, there are rubber mats designed for this purpose if the feeder runs on a floor, and if mutual conductor heating is not problematic, raceway protection is another option.
Part (N) specifically recognizes terminals to which stage cables may be connected to be located where access will be “convenient.” Note that this does not mention a power outlet as covered in 520.51, which adds strength to the argument that in the entire context of 520.51 and 520.53 other connections are permitted. There is no upper size limit, or a maximum number of parallel conductors permitted, on the terminals covered here.
Part (O) covers special rules for feeder neutrals. The first paragraph requires the neutral busbars and connecting supply terminal on a 3-phase 4-wire portable switchboard to “have an ampacity” not less than twice the “ampacity of the largest ungrounded supply terminal.” Note that this phrasing is a violation of the NEC Style Manual because terminals [and also overcurrent devices as described in 520.53(H)(3&4)] do not possess ampacity, only (in this case) an ability to terminate conductors with a specified ampacity. This oversizing allows these portable switchboards to be connected to single-phase systems where two phases will be connected to one phase line, potentially doubling the neutral current. If the portable switchboard has been specifically designed for field rearrangement from single- to three-phase and back again with the single-phase loading being left in balance when used, then the double size requirement is waived.
The second paragraph requires that the ampacity of a neutral on a multi-phase system feeder to a portable stage switchboard must have an ampacity of 130 percent of the ungrounded conductors in cases where the feeder is run as single conductor cables. This rule only applies to single conductor uses, where the customary 125 percent increase in size for four conductors in a raceway or cable will not apply. This rule is due to the electrical characteristics of typical stage dimmer circuits and is not a response to the more general problem of harmonic currents. The US Institute of Theatre Technology presented an analysis that the worst case loading would occur when one phase was off, one phase was 100 percent loaded, and the third phase loaded to 55 percent; this would produce a 126 percent load on the neutral. For multiconductor cables, the harmonic content means the neutral is counted, resulting in a 125 percent factor already and this is judged sufficient to handle this loading. However, for single conductor cables, no such rule applies, so this section imposes a 130 percent factor. As in other comparable applications, the extra loading requirement is waived if the entire dimming system uses the new solid-state sine wave dimmers.
Part (P) requires portable stage switchboards to be connected by qualified personnel, and they must be conspicuously marked to indicate this requirement. An exception applies to smaller feeders 150 A and below using multipole receptacle outlets. The qualified personnel requirement applies to routing conductors, as well as to making and breaking connections and to energizing and de-energizing the switchboards. The exception only applies where a multipole, permanently installed receptacle outlet has overcurrent protection not above its rating and where it is not accessible to the general public. Extra-hard usage cord with an ampacity equal to the receptacle rating must be used. The concept is that if the only task is to plug in a multiconductor cord into an appropriately located power outlet, the work can be left to an amateur.
520.61. Arc Lamps. This section requires that all arc lamp fixtures must be listed, including any associated ballasts and interconnecting cables and cord sets. The term “arc lamp fixture” is intended to include all fixtures that rely on an arc lamp as the source of light, whether carbon-arc or HID. The motivation for the current wording came from concerns about extremely high-energy lighting sources that are being used in stage settings. Some of these sources use 24,000 W lamps with 90,000 V ignition circuits.
520.65. Festoons. “Lanterns or similar devices” are very likely to be made of paper or other flammable material, and the lamps should be prevented from coming in contact with such material. Staggering the joints lessens the likelihood of a line-to-line arcing fault that could start a fire in such lamps. Note that 225.24, which makes the same requirement for outside lighting, also requires that lampholders using pin connectors that puncture conductor insulation to make a connection must only be used on stranded wire. Although that rule technically only applies within the scope of Art. 225, it should be applied here as well.
520.68. Conductors for Portables. The basic rule is for listed extra-hard usage flexible cord. Stand lamps are permitted with hard-usage cord. Luminaires operating at high temperatures are permitted with a 1.0 m (3.3 ft) connection typically consisting of some form of high-temperature fixture wire enclosed in a glass braid of some sort, and terminating in a pin-type stage plug. The braid is clamped by the plug housing and the luminaire connection, which provides a measure of strain relief. Para. 4 covers “breakout assemblies” and allows them to be made of hard usage cord. They allow for one or multiple branch circuits to be taken out of a multiconductor cable that may have as many as 37 conductors within it. The use of hard usage cord allows this to be done on a practical basis, and is appropriate given the conditions placed on their use. Limited to 20 A circuits, the branch cable cannot exceed 6.0 m (20 ft) and must be routed over its length attached to structure or other rigid supports. Note that this rule is not restricted to the supply of cord bodies, and that breakout plug assemblies are also available, in accordance with the same rules.
Part (B) allows cord ampacities and maximum currents to follow Table 520.44 unless they are in direct contact with “heat producing elements,” in which case the usual 400.5 provisions apply. The fixture wires used in accordance with 520.68(A)(3) use conventional code ampacity provisions, which in this case would be Table 402.5.
520.69. Adapters. The “two-fer” (a male plug made up with a molded splice generally configured in a wye arrangement to feed two female receptacles) is a good example of the use of this section. The current and voltage ratings of the plug and the receptacles supplied must be identical, with no reduction in current rating to either branch. See 520.67 for additional requirements. The conductors must be listed extra-hard usage cord. Alternatively, hard usage cord with its overall length limited to 1.0 m (3.3 ft) can be used.
520.72. Lamp Guards. Lamps in dressing rooms should be provided with guards that cannot easily be removed to prevent them from coming in contact with flammable material.
520.73. Switches Required. The luminaires and receptacles located adjacent to the mirrors and above a dressing table in a dressing room must be controlled by one or more wall switches located in the dressing room but equipped with pilot circuits brought out to a point near the dressing room door. This allows supervisory personnel to quickly determine if likely loads in the dressing areas are still connected.
This article is new in the 2008 NEC. It covers the unique wiring requirements of permanent theme parks and comparable attractions, such as Disney World. There are almost 500 of these parks now operating in the United States, and many others in different countries that also use the NEC for their electrical installation standard. It is a very unusual article in that it does not cover power circuits, only the controls for equipment connected to power circuits. As such it recognizes and provides an ampacity table for conductor as small as 30 AWG.
525.1. Scope. The rules given here apply to the wiring of temporary power used to supply power to rides and amusements at circuses, and so on. However, it should be remembered that, unless otherwise modified by Art. 525, the requirements given in Chaps. 1 through 4 also apply.
525.3. Other Articles. This article doesn’t apply within permanent structures; Art. 518 and 520 apply instead. Art. 640 applies to audio signal and related wiring and equipment. Art. 680 (presumably focusing on Part I on general rules and Part III on storable applications, but the reference, to the entire article in violation of the whole-article reference prohibition in the NEC Style Manual, is extremely unclear) applies to attractions using contained volumes of water.
525.5. Overhead Conductor Clearances. Portable structures must not be placed under or within 4.5 m (15 ft) horizontally of overhead medium-voltage conductors, including utility primaries arranged on adjacent poles. The 4.5 m (15 ft) clearance also applies in any direction from overhead wiring at 600 V and below, except for the supply conductors to the structure.
525.10. Services. If in locations accessible to unqualified persons, service equipment must be lockable. It must be on solid backing and protected from weather (unless weatherproof).
525.11. Multiple Sources of Supply. If multiple power sources, such as two different generator wagons, supply adjacent portable structures, the equipment grounding conductors of both sources must be bonded together if the structures are separated by less than 3.7 m (12 ft). The size of the bonding conductor must not be less than the required size of an equipment grounding conductor that would be used (per Table 250.122) based on the largest overcurrent device supplying load in either of the two structures, but in any case not smaller than 6 AWG.
525. 20. Wiring Methods. The principal wiring method for traveling carnivals is flexible cord. As presented in (A), for general use it should be listed for extra hard service and for outside venues, listed for sunlight resistance and wet locations as well. Single-conductor cable is not permitted below 2 AWG, and splices are not permitted. Cord connectors must not be laid in traffic paths or within areas accessible to the public unless guarded. They must not be laid on the ground unless booted or otherwise made suitable for wet locations. They must be arranged so they do not create a tripping hazard, and they should be covered with low-profile matting that does not increase the tripping hazard. They can be pushed into a slit in the ground and then taken up because 525.20(G) waives 300.5 for these events. The conductors must only be spliced in boxes or in a comparable enclosure.
525.21. Rides, Tents, and Concessions. Each “structure” which would include rides such as Ferris Wheels, etc. must have a disconnecting means within 1.8 m (6 ft) of the operator’s station at a readily accessible point while the ride is operating. A shunt trip device controlled from the operator’s console is acceptable for this purpose. Wiring in tents and concession stands must be securely supported and provided with mechanical protection if subject to damage. Lamps must be either mounted within a luminaire or equipped with guards.
525.22. Portable Distribution or Termination Boxes. If used outdoors, these boxes must be arranged to sit at least 150 mm (6 in.) above the ground, and of weatherproof construction. The overcurrent protection ahead of the box must not exceed the current rating of any included busbars. Where the box includes receptacles, overcurrent protection must be included within the box, rated not higher than the receptacles.
525.23. Ground-Fault Circuit Interrupter (GFCI) Protection. As covered in part (A), all 15- and 20-A, 125-V rated non-locking-type receptacles and equipment accessible to the general public must be provided with GFCI protection for personnel protection. There is no waiver for equipment incompatible with a GFCI, as in the recent past. The idea is that if a GFCI is nuisance tripping, the appliance should be repaired or replaced. There are many old popcorn popping machines and comparable equipment with an electrical resistance inserted into refractory material that is somewhat conductive until it heats up and drives the water out of the refractory insulation. Until that happens, a GFCI will nuisance trip. However, it is also true that modern equipment designs do not have this shortcoming. In part (B) the Code states that there is no need for locking-type receptacles to be GFCI protected. This rule, for “quick disconnecting and reconnecting” is aimed at the multiple connections of lighting strips and other connections on large rides. And (C) states that circuits supplying egress lighting are prohibited from employing GFCI protection.
525.32. Grounding Conductor Continuity Assurance. Each time portable electrical equipment is deployed, the continuity of the grounding system must be verified. This would presumably take place during the final stages of set-up at each venue. The electrical inspection community may need to stipulate timing and access so as to be able to judge compliance with this requirement
530.1. Scope. Article 520 covers theaters used for TV, motion picture, or live presentations where the building or part of a building includes an assembly area for the audience. Article 530, however, applies to TV or motion picture studios where film or TV cameras are used to record programs and to the other areas of similar application, but where the facility does not include an audience area.
The term motion picture studio is commonly used as meaning a large space, sometimes 100 acres or more in extent, enclosed by walls or fences within which are several “stages,” a number of spaces for outdoor setups, warehouses, storage sheds, separate buildings used as dressing rooms, a large substation, a restaurant, and other necessary buildings. The so-called stages are large buildings containing numerous temporary and semipermanent setups for both indoor and outdoor views.
The Code rules for motion picture studios are intended to apply only to those locations where special hazards exist. Such special hazards are confined to the buildings in which films are handled or stored, the stages, and the outdoor spaces where flammable temporary structures and equipment are used. Some of these special hazards were due to the presence of a considerable quantity of highly flammable film, but this is rarely the case today since nitrocellulose film was discontinued in the early 1950s; otherwise, the conditions are much the same as on a theater stage and, in general, the same rules should be observed as in the case of theater stages. The rules in this article also amend provisions in Chap. 1 through 4 in ways that reflect some unusual load profiles and time factors that make possible special allowances.
530.11. Permanent Wiring. At one time, this section used the word metal between “approved” and “raceways,” in the first sentence. Because the word metal no longer appears in the rule, rigid nonmetallic conduit is, therefore, acceptable for use in motion picture and TV studios. In addition to raceways, Type MI and Type MC cables and Type AC cable with an insulated grounding conductor are also permitted.
In the exception, Class II and III remote-control or signaling circuits and power-limited fire-protective signaling circuits are exempted from the basic rule requiring permanent wiring to be in raceways or certain cables. These circuits, along with communications and sound recording and reproducing circuits, are exempt from the basic rule.
530.12. Portable Wiring. Wiring that would be subject to physical damage needs to be extra-hard usage cord; otherwise hard usage is permitted. Splices are permitted provided the load doesn’t exceed the cable ampacity. Stage effect wiring can be either single or multiple conductor listed cord, provided it is protected from damage and secured to the scenery with cable ties or insulated staples. Splices are permitted only with listed devices on circuits not over 20A. For other equipment, cords that aren’t suitable for extra hard usage are permitted if shipped as part of a listed assembly and protected at not over 20 A.
530.13. Stage Lighting and Effects Control. This section covers the use of “location boards” as defined in 530.2. They are a form of switchboard with fused switches or circuit breakers typically in the 200 A range protecting 3-wire circuits, so they can be used to source 200 A of line-to-neutral load on both ungrounded supply legs (total of 400 A). This equipment is usually mounted with casters and also often has a pulling eye in the upper surface so it can be hoisted to an elevated walkway. The common “deuce” board has two such switches, allowing it to supply double that amount of power. Usually contactors are arranged within the boards at a point where the board can be turned off or on all at once, or busbar by busbar. A local switch must be placed within 1.8 m (6 ft) of the board for each contactor, or a single switch that drops out all the contactors at once is also permitted. Today, it is common for these boards to be controlled at the stage level by incorporating suitable electronic controls that govern the switching activity within the board.
530.14. Plugging Boxes. At one time these were used on both ac and dc circuits, however they are unpolarized, which led to hazards when ac equipment designed with single-pole switching was connected. They were generally limited to dc applications, and effective with the 1987 NEC, ac connections are not permitted.
530.17. Portable Arc Lamps. At one time the only practical source of intensely white light in amounts large enough to illuminate studio sets came from drawing a dc arc between two carbon electrodes. The carbon electrodes would gradually burn back in the process, requiring them to be constantly advanced so the gap would remain constant. Early designs relied on manual supervision; later designs used mechanized methods to do the same thing. The current required for large scale illumination were impressive, running on the order of 150A. The development of xenon filled high intensity discharge lighting (introduced in 1954) made carbon arc light sources essentially obsolete by the 1970s, but many facilities still have the dc infrastructure in place. The xenon sources including their ballasts must be listed. These lamps operate with a color temperature of about 6200°K (about the same as the sun) and a color rendering index (CRI) only slightly below 100 percent.
530.18. Overcurrent Protection—General. Part (A) allows stage cables to be protected at 400 percent of their ampacity, and this percentage carries through in (B), (D), and (E). It is a short-time rating and is based on the time that the conductors are energized during production, generally on the order of 10 min and not over 20 min. Part (C) covers cable protection and roughly parallels 520.53(H)(5), covered extensively in this book, in order to address similar concerns. Note that the final sentence of the parent text at the beginning of the section specifically requires that conductors be sized in accordance with the load to be supplied. This sentence clarifies that although the overcurrent protection can be rated up to 400 percent of ampacity, it is never permitted to impose loads on conductors greater than normal code rules permit. The 400 percent rule allows for flexibility of arranging circuits, and does not justify overloading conductors. Studio equipment undergoes testing based on the higher overcurrent protection values permitted in this article.
530.19. Sizing of Feeder Conductors for Television Studio Sets. This section provides a table of demand factors that allow reductions in total feeder capacity for permanent studio and stage set lighting feeder loads. Portable feeders enjoy a blanket 50 percent demand factor.
530.21. Plugs and Receptacles. Part (A) covers ratings, which must not be less than the circuit voltage, and for ac circuits, the ampere ratings not less than the feeder or branch-circuit overcurrent device rating. Table 210-21(b)(2) does not apply. This is a similar allowance as in 520.9 for theatrical work. It allows fully rated and potentially fully loaded 20 A cord- and plug-connected loads to plug into multi-outlet 20 A branch circuits, which would otherwise be limited to 16 A by Table 210-21(b)(2). Some stage set lighting loads, such as 10,000-W 120-V luminaires, exceed 80 A.
Part (B) covers plugs and receptacles used in portable professional motion picture and television equipment, which can be interchangeable for ac or dc use on the same premises provided they are listed for ac/dc use and marked in a suitable manner to identify the system to which they are connected. Both types of power are commonly in use on the same premises in today’s studios.
530.22. Single-Pole Separable Connectors. This section parallels 520.53(K), for which this book has complete coverage. Part (B) adds the ac/dc interchangeability principle in 530.21(B) to this location as well.
530.41. Lamps at Tables. This section, essentially unchanged for over 70 years, requires luminaire construction at film editing tables to be constructed in ways that make ignition of film scrap unlikely. This rule is rooted in the days of nitro-cellulose film (a compound also known as guncotton), which is extremely flammable; however, it is unsuitable for color photography and has not been produced for almost 60 years.
530.51. Lamps in Cellulose Nitrate Film Storage Vaults. This section and the one following are another relic of another time, although some old prints are still archived. The goal is to keep all potential ignition sources away from the film. This film is so easy to ignite it has been known to spontaneously burst into flames and some spectacular (and horribly destructive) fires resulted as flames spread from reel to reel. These fires are extremely difficult to control because the nitrate component is a powerful oxidizing agent capable of sustaining combustion even under water. In addition, unless kept cool the film is chemically unstable because the nitrate component is also capable of forming nitric acid, which turns the film into a gelatinous mass. There have been many concerted efforts, largely successful, to convert the remaining old stock into modern film bases that do not have these problems.
530.61. Substations. This part of the article reminds us of the scale of motion picture sets and associated activities. The use of medium-voltage feeders to remote locations to support the large power demands during filming is often a necessary fact of life, with special allowances for work space reductions. The use of dc, still recognized here, is not as essential as it was during the time of carbon arc lighting. Here again, however, many facilities still operate dc distributions.
540.1. Scope. According to the definition of hazardous locations in Art. 500, a motion picture booth is not classed as a hazardous location, even though even the old nitrocellulose film is highly flammable. The film is not volatile at ordinary temperatures, hence, no flammable gases are present, and the wiring installation need not be explosionproof but should be made with special care to guard against fire hazards.
540.2. Definitions. Figure 540-1 shows a professional projector, which is subject to lengthier and stricter requirements than those of nonprofessional movie projectors. The one shown, with ventilating duct work over the top of it, is a carbon-arc projector. A special form of high-intensity discharge lamp using a xenon gas fill has supplanted these older projectors, although some still exist in art houses. Refer to the discussion in the previous chapter (at 530.17) for more information on carbon-arc light sources.
540.10. Motion Picture Projection Room Required. Professional projectors must be installed in a projector booth, which as noted does not have to be treated like a hazardous (classified) location.
Figure 540-2 shows the arrangement of the apparatus and wiring in the projection room of a large, modern motion picture theater. This room, or booth, contains three motion picture projectors P, one stereopticon or “effect machine” L, and two spot machines S. This method of projection has been functionally obsolete for over 30 years having been supplanted by xenon arc discharge lamps, just as in the case of motion picture studio set lighting as noted in the commentary in the previous chapter at 530.17. However, arc-lamp projection is still used in some art houses and since this NEC article is largely still written around this technology, coverage in this book has been retained.
Fig. 540-1. Professional projector. But note that Art. 540 applies to both professional and nonprofessional movie projectors. The article is divided into part III on professional equipment and part IV on nonprofessional units. (Sec. 540.10.)
The light source in each of the six machines is an arc lamp operated on dc. The dc supply is obtained from two motor-generator sets, which are installed in the basement in order to avoid any possible interference with the sound-reproducing apparatus. The two motor generators are remotely controlled from the generator panel in the projection room. From each generator, a feeder consisting of two 500-kcmil cables is carried to the dc panelboard in the projection room.
From the dc panelboard to each picture machine and to each of the two spot machines, a branch circuit is provided consisting of two 2/0 AWG cables. One of these conductors leads directly to the machine; the other side of the circuit is led through the auxiliary gutter to the bank of resistors in the rheostat room and from its rheostat to the machine. The resistors are provided with short-circuiting switches so that the total resistance in series with each arc may be preadjusted to any desired value.
Fig. 540-2. Code rules cover many electrical details in a motion-picture projection room (or “booth”). (Sec. 540.10.)
Two circuits consisting of 1 AWG conductors are carried to the stereopticon or “effect machine,” since this machine contains two arc lamps.
The conduit leading to each machine is brought up through the floor. 540.13 specifies that the wires to the projector outlet should not be smaller than 8 AWG, but in every case the maximum current drawn by the lamp should be ascertained and conductors should be installed of sufficient size to carry this current. In this case, when suitably adjusted for the large pictures, the arc in each projector takes a current of nearly 150 A.
In addition to the main outlet for supplying the arc, four other outlets are installed at each projector machine location for auxiliary circuits. Outlets F are for foot switches that control the shutters in front of the lenses for changeover from one projector to another. Outlets G are for an 8 AWG grounding conductor, which is connected to the frame of each projector and to the water-piping system. From outlets C, a circuit is brought up to each machine for a small incandescent lamp inside the lamp house and a lamp to illuminate the turntable. Outlets M are for power circuits to the motors used to operate the projector machines.
Ventilation is provided by two exhaust fans and two duct systems, one exhausting from the ceiling of the projection room and one connected to the arc-lamp housing of each machine. (See Fig. 540-1.)
A separate room is provided for rewinding films, but since this room opens only into the projection room, it may be considered that the rewinding is performed in the projection room.
Modern projectors have integral rectifiers that eliminate the need for remote dc generators, and also different light sources than the old dc arc lamps, as previously noted in this chapter and in the discussion at 530.17. A typical branch circuit for a modern xenon professional projector would run between 20 and 60 A on a 208Y/120 V 4-wire branch circuit (5000 W being a common size). The projector sizing is based on the film and screen size, which in turn governs the size of the projector and the related requirements for the lamp house. This then eliminates the motor generator, making both building and electrical construction far simpler. Note, however, that even under the usual conditions where xenon arc lamps are used as the light source, the requirements in this section for all projection ports, etc. to be closed with glass or other approved material still apply.
540.11. Location of Associated Electrical Equipment. All necessary equipment may be located in a projector booth, but equipment which is not necessary in the normal operation of the motion picture projectors, stage-lighting projectors, and control of the auditorium lighting and stage curtain must be located elsewhere. Equipment such as service equipment and panelboards for the control and projection of circuits for signs, outside lighting, and lighting in the lobby and box office must not be located in the booth, although remote controls for auditorium lights and curtain and screen adjustments are allowed for obvious reasons.
Part A of this section includes enhanced precautions to be used around nitrocellulose film, which parallel and build on the ones in 530.52. As noted in the discussion at 530.51, this film is long obsolete, but if an old print is screened, the precautions are appropriate. Part (B) includes an exception essentially waiving the equipment segregation rules if only safety film (i.e., other than nitrocellulose) will be used and provided the projection booth is provided with signage both within its confines and also on the door, clearly stating that only safety film is allowed in the room. Part (C) correlates these rules with Art. 700, including 700.21 that prohibits the placement of the only switch that can energize emergency lighting within a projection booth.
540.12. Work Space. The customary 750 mm (30 in.) of work space width about equipment that must be worked while energized also applies on each side of projection equipment, although the spaces to the sides may overlap where adjacent projection equipment is in use.
540.14. Conductors on Lamps and Hot Equipment. If equipment will be operating above 50°C (122°F) its supply conductors must be rated not less than 200°C (392°F). This could be a difficult requirement to meet if flexible cord is required for the application.
540.31. Motion Picture Projection Room Not Required. Assuming safety film is used, nonprofessional projectors do not require a projection booth. Such projectors must, however, be listed.
545.1. Scope. This article covers prefabricated buildings delivered to a permanent foundation on flatbed trucks and put in place with a crane. They have no chassis framing and no running gear and therefore no capability to be towed. In this way they differ fundamentally from “Manufactured Homes” as covered in Art. 550.
545.4Wiring Methods. Any Chap. 3 wiring method is permitted if otherwise permitted for the location. Where run in closed construction, cabled wiring is the equivalent of fished, and therefore a comparable allowance for securement only at the connectors. The cable size cannot exceed 10 AWG for this to be allowed.
545.10. Receptacle or Switch with Integral Enclosure. These are wiring devices without boxes, as permitted in 300.15(E).
545.13. Component Interconnections. When sections of a manufactured building must be mated in the field, the cabled interconnections (usually Type NM cable), need to be joined and there are listed devices that make up cable to cable and wire by wire within each cable, resulting in a field splice that is the equal of the cable as a whole. This section amends the usual requirements for a box at this point, and allows these devices to be used. Their track record is very good.
547.1. Scope. Any agricultural building without the environments covered in parts (A) and (B) must be wired in accordance with all other Code rules that apply to general building interiors. Article 547 covers only agricultural buildings with the dust, water, and/or corrosive conditions described in parts (A) and (B).
547.5. Wiring Methods. The wording leaves much of the determination of acceptability up to the inspection authority. But Type NMC cable (nonmetallic, corrosion-resistant—so-called barn wiring cable), UF, jacketed Type MC, or copper SE are specifically recognized for these buildings. PVC conduit and other nonmetallic or protected products including liquidtight flexible non-metallic conduit would be suitable for the wet and corrosive conditions that prevail. The rule also accepts wiring for Class II hazardous locations in locations covered by 547.1(A) in the scope (excessive dust).
Note that boxes and fittings must be both dust- and watertight in instances where corrosive and wet conditions warrant the attention. Flexible connections must use dusttight flex or liquidtight flex or cord. Also note that nonmetallic boxes, fittings, and so on, are exempt from the provisions of 300.6(D). If such components and cables are made from a metallic material, then the¼-in. (6.35-mm) clearance called for in 300.6(D) would apply.
547.6. Switches, Receptacles, Circuit Breakers, Controllers, and Fuses. In this part, the description of the type of enclosure required corresponds to the following NEMA designations on enclosures:
Type 4: Watertight and dusttight. For use indoors and outdoors. Protect against splashing water, seepage of water, falling or hose-directed water, and severe external condensation. They are sleet-resistant but not sleet- (ice-) proof.
Type 4X: Watertight, dusttight, and corrosion-resistant. These have the same provisions as Type 4 enclosures, but in addition are corrosion-resistant.
The rule of this section seems to clearly call for NEMA 4X enclosures (Fig. 547-1).
Fig. 547-1. The Code rule seems to make use of this type of enclosure mandatory in agricultural buildings. (Sec. 547.5.)
Stainless steel NEMA Type 4X enclosures are used in areas which may be regularly hosed down or are otherwise very wet, and where serious corrosion problems exist. Typical enclosures are made from 14-gauge stainless steel, with an oil-resistant neoprene door gasket.
Epoxy powdered resin–coated NEMA Type 4X enclosures are designed to house electrical controls, terminals, and instruments in areas which may be regularly hosed down or are otherwise very wet. These enclosures are also designed for use in areas where serious corrosion problems exist. They are suitable for use outdoors, or in dairies, packing plants, and similar installations. These enclosures are made from 14-gauge steel. All seams are continuously welded with no holes or knockouts. A rolled lip is provided around all sides of the enclosure opening. This lip increases strength and keeps dirt and liquids from dropping into the enclosure while the door is open.
547.9. Electrical Supply to Building(s) or Structure(s) from a Distribution Point.Figure 547-2 shows a typical overhead distribution at a farm. The central pole is defined in 547.2 as the distribution point for the farm. Since this pole top is both the metering point and the service point for the utility, there will be a switch here, as shown in Fig. 547-3. The disconnecting means may be provided by the utility or by the owner, depending on local practice. The switch has no overload protective devices within it, thereby varying from the normal rule for services in NEC 230.91. The NEC classifies this device in 547.2 as a site isolating device to distinguish it from a service disconnect. Even if supplied and maintained by the utility, and therefore beyond the scope of the NEC, the NEC avoids needless duplication by recognizing it as a disconnecting means provided it meets the requirements in NEC 547.9(A).
Since it is not an actual service disconnect, it follows that the wiring that leaves this device still has the status of service conductors and must meet the wiring method and clearance requirements in Art. 230. Although nothing technically prevents a farm from establishing a conventional service at the distribution pole, and then routing conventional overcurrent-protected feeders to each building, the arrangement shown here is widely used for overall cost effectiveness. Note that although the switch is at the top of the pole, it can be operated from a readily accessible point through the permanently installed linkage shown in Fig. 547-3. In addition, a grounding electrode conductor must be installed at this point and run it from the neutral block of the switch to a suitable electrode at the pole base.
Fig. 547-2. Overhead distributions on farms usually involve one or more distribution points. (Sec. 547.9.)
Fig. 547-3. This is a site isolating device for a farm, showing the drops to the house and a barn. (Sec. 547.9)
Part (E) requires that if there are two or more distribution points located closer together than 150 m (500 ft) (measured in a straight line), each location must have reciprocal labeling setting out the location of the other point(s) and the buildings or structures served by each.
Part (D) requires that where livestock is housed, any portion of an equipment grounding conductor that is directly buried must be insulated or covered copper.
Part (B) governs the wiring of the service conductors from the site isolating device to the various buildings that will be served directly, as shown in Fig. 547-2, and as detailed at the site isolating device by Fig. 547-3.
As a general rule the farmhouse can be supplied by a three-wire service, with its neutral regrounded at the house just as if the utility had made a direct termination. The farmhouse must not, however, share a common grounding return path with the barn. If it does, as in the case of a common metallic water piping system, the house (1) has to be supplied with a four-wire service, and (2) have all instances of electrical contact between the neutral and the local equipment grounding system removed.
Although the barn, arguably, could also be wired like the house (three-wire), a three-wire hook-up would mean that the neutral and the equipment grounding system in the barn would be bonded together at the barn disconnect. That in turn would mean the neutral, in the process of carrying current across its own resistance, would constantly elevate the voltage to ground of all barn equipment by some finite amount relative to local ground, especially from the perspective of farm animals where they stand. The feet of livestock, being in close contact with moisture, urine, and other farm chemicals, is conductively rather well-coupled to local earth. Most livestock are much more sensitive to voltage gradients than are people. A potential difference in the range of a fraction of a volt can take a cow out of milk production, which no farmer can afford.
The NEC addresses this in two ways. First, it establishes the unique rules on farm distributions being covered here. Second, it establishes an equipotential plane for these environments, covered in 547.10. The service to the barn is normally wired four-wire, and that is (1) customary because of the reasoning discussed in the previous paragraph, and (2) mandatory unless there are no parallel grounding return paths over water systems, etc., a necessary condition to comply with NEC 250.32(B) Exception. There is an additional condition [see 547.9(B)(3)] attached to the four-wire scheme that is unique to agricultural buildings. The separate equipment grounding conductor must be fully sized. That is, if the run to the barn is 3/0 AWG copper for a 200-A disconnect, and the neutral is 1/0 AWG copper (both sized on the basis of load), the equipment grounding conductor is not 6 AWG as normally required by NEC Table 250.122; nor is it 4 AWG, the size for a grounding conductor on the supply side of a service using 3/0 AWG wires; nor is it 1/0 AWG, the size of the neutral. It must not be smaller than the largest ungrounded line conductor, or 3/0 AWG. When this wire arrives at the barn, it must arrive at a local distribution with the neutral completely divorced from any local electrodes or equipment surfaces requiring grounding.
547.10. Equipotential Planes and Bonding of Equipotential Planes. Due to the sensitivity of livestock to very small “tingle” voltages, the NEC now requires an equipotential plane in livestock (does not include poultry) confinement areas, both indoors and out, if they are concrete floored and contain metallic equipment accessible to animals and likely to become energized. These areas must include wire mesh or other conductive elements embedded in (or placed under) the concrete floor, and those elements must be bonded to metal structures and fixed electrical equipment that might become energized, as well as to the grounding electrode system in the building. In the case of dirt confinement areas, the equipotential plane may be omitted. For outdoor areas the plane must encompass the area in which the livestock will be standing while accessing equipment likely to become energized.
Remember that the grounding system to which equipotential planes should be connected is usually (refer to the discussion on 547.9) electrically separated from neutral return currents. The idea is to minimize voltage gradients. Due to the well-grounded environment, the NEC also requires [see 547.5(G)] all general purpose 15- and 20-A, 125-V receptacles in the area of an equipotential plane to have GFCI protection. This GFCI protection requirement also applies to similar receptacles in all damp or wet locations, including outdoors, and for dirt confinement areas whether indoors or out. Receptacles for specified (not general purpose) loads are not covered by this requirement, but where GFCI protection is omitted, a GFCI-protected receptacle must be installed within 3 ft of the unprotected receptacle.
550.1. Scope. The provisions of this article cover the electric conductors and equipment installed within or on mobile homes and manufactured homes, and also the conductors that connect mobile homes and manufactured homes to a supply of electricity. But the service equipment which is located “adjacent” to the mobile home is covered in Art. 550 and all applicable Code rules on such service equipment—as in Arts. 230 and 250—must be observed.
550.2. Definitions. The difference between a mobile home and a manufactured home is that although both buildings have a chassis and are designed to move on running gear, the mobile home is not intended to be placed on a permanent foundation. Most buildings in this category today are manufactured homes, produced with the expectation that they will ultimately rest on a permanent foundation. A manufactured home is not a manufactured building covered in Art. 545.
They also enjoy a protected regulatory status, because the federal Department of Housing and Urban Development (HUD) has determined that they are a solution to the lack of housing. Therefore, acting under the supremacy clause in the U.S. constitution with authority delegated by a congressional enactment, HUD has decreed that what passes muster under their regulations regarding the manufacture of these homes will be accepted by local enforcement agencies. This is why the version of the NEC that applies to any particular manufactured home is usually not synchronized with local adoption of the NEC.
The definition for “manufactured home” clarifies when the service equipment may be hung on the dwelling. The service may never be installed on, or in, a mobile home. But where a manufactured home meets the requirements of 550.32(B) which include provisions for a permanent foundation (and almost all do), it may be supplied by a service that is installed adjacent to or even on or in the manufactured home. Notice that the last sentence in the definition makes all rules for “mobile homes” applicable to “manufactured homes” as well.
550.4. General Requirements. Part (A) covers mobile homes that are not for residential purposes, such as construction trailers and the like. Such buildings need not comply with the rules regarding the number and capacity of circuits, but they must comply with the other applicable rules, including the requirement in 550.32(A) that the service not be mounted in or on the trailer (mobile home).
550.10. Power Supply. Part (A) requires that the power supply to the mobile home be a feeder circuit consisting of not more than one 50-A rated approved mobile home supply cord, or that feeder circuit could be a permanently installed circuit of fixed wiring (Fig. 550-1). An exception correlates with allowances for these dwellings to be supplied directly with service wiring if they meet the definition of a “manufactured home.”
Fig. 550-1. Service equipment for a mobile home lot consists of disconnect, overcurrent protection, and receptacle for connecting one 50-A (or 40-A) power-supply cord from a mobile home parked adjacent to the service equipment. (Sec. 550.10.)
Part (B) covers use of a cord instead of permanent wiring. The power-supply cord to a mobile home is actually a feeder, and must be treated as such in applying Code rules. The service equipment must be located adjacent to the mobile home and could be either a fused or a breaker type in an appropriate enclosure or enclosures, with not more than 50-A overcurrent protection for the supply cord (or 40 A, as in the exception). The equipment must be approved service-entrance equipment with an appropriate receptacle for the supply cord, installed to meet Code rules the same as any installation of service equipment. The panel or panels in the home are feeder panels and are never to be used as service-entrance equipment, according to 550.10 and 550.11(A). This means that the neutral is isolated from the enclosure and the equipment grounding goes to a separate bus for that purpose only. As a result, there must be an equipment grounding conductor run from the service-entrance equipment to the panel or panels in the home. This is true whether there is cord connection or permanent wiring.
In some areas, mobile homes are permanently connected as permitted in paragraph (I). Accordingly, local requirements must be checked in regard to the approved method of installing feeder assemblies where a mobile home has a calculated load over 50 A. In many such cases, a raceway is stubbed to the underside of a mobile home from the distribution panelboard. It is optional whether the feeder conductors are installed in the raceway by the mobile home manufacturer or by field installers. When installed, four continuous, insulated, color-coded conductors, as indicated, are required. The feeder conductors may be spliced in a suitable junction box, but in no case within the raceway proper.
550.11. Disconnecting Means and Branch-Circuit Protective Equipment. As shown in Fig. 550-2, the required disconnect for a mobile home may be the main in the panelboard supplying the branch circuits for the unit. Details of this section must be observed by the mobile home builder.
Fig. 550-2. A “distribution panelboard,” not “service panelboard” may be used in mobile home. (Sec. 550.11.)
550.12. Branch Circuits. The manufacturer of the mobile home must ensure this minimum circuiting.
550.13. Receptacle Outlets. These rules generally line up with comparable rules in Art. 210, but one cycle behind. As changes occur in Chap. 2, this article tends to be updated in the next cycle. For example, the disallowance of a snap-switch controlled receptacle to meet a placement rule in 210.52, a 2008 NEC change, is not yet correlated with this article. Part (E) for the heat tape receptacle outlet, however, is unique to this article. The heat tape outlet (“pipe heating cable”) must now have GFCI protection, and it must be arranged so tripping the GFCI protection would be obvious to the occupant. Accordingly the outlet must go on an interior circuit arranged with all other outlets on that circuit on the load side of the GFCI protective device. A bathroom, but not a small appliance, branch circuit could be chosen for this purpose. Note that the GFCI protection, provided by a residual current device, also effectively complies with 427.22. Small appliance branch circuits can only serve their intended outlets as covered in 210-52(B), so this correlates with that provision. Note also that 550-12(B) makes no amendments to Chap. 2 in this regard.
550.15. Wiring Methods and Materials. In the exception to part (I), the smaller-dimensional box mentioned would usually be a box designed for a special switch or receptacle, or a combination box and wiring device. Such combinations can be properly evaluated and tested with a limited number of conductors and connections and a specific lay of conductors to ensure adequate wiring space in the spirit of 314.16.
550.16. Grounding. The white (neutral) conductor is required to be run from the insulated busbar in the mobile home panel to the service-entrance equipment, where it is connected to the terminal at the point of connection to the grounding electrode conductor.
The green-colored conductor is required to be run from the panel grounding bus in the mobile home to the service-entrance equipment, where it is connected to the neutral conductor at the point of connection to the grounding electrode conductor.
The requirements provide that the grounded (white) conductor and the grounding (green) conductor be kept separate within the mobile home structure in order to secure the maximum protection against electric-shock hazard if the supply neutral conductor should become open.
A common point of discussion among electrical authorities and electricians is whether the green-colored grounding conductor in the supply cord should be connected to the grounded circuit conductor (neutral) outside the mobile home—say, at the location of the service equipment. The grounding conductor in the supply cord or the grounding conductor in the power supply to a mobile home is always required to be connected to the grounded circuit conductor (neutral) outside the mobile home on the supply side of the service disconnecting means, but not in a junction box under the mobile home or at any other point on the load side of the service equipment (pedestal).
550.18. Calculations. This section provides the rules for making load calculations for mobile homes. These provisions generally track the provisions for comparable loads in other dwelling occupancies. For example a 12 kW range is a 8 kW load. However, for a home on a 40-A cord and no air-conditioner, 15 A per leg must be allowed for a future air-conditioning load. Part (C) allows the optional calculations in 220.82 to be used without amendment, but interestingly does not recognize the somewhat more forgiving provisions of 220.83 to be used for existing units.
550.25. Arc-Fault Circuit-Interrupter Protection. This is an excellent example of how this article tends to lag Chap. 2 by a cycle, with AFCI rules only applying to outlets in bedrooms as was the case in ordinary dwelling units in the 2005 NEC. Even this version of AFCI, far from the virtual whole-house protection requirements of 210.12 in the NEC for this cycle, may or may not reflect current HUD 3280 rulemaking and therefore what is being shipped in interstate commerce. Refer to the discussion at 550.2 for more information on this point.
550.30. Distribution System. The mobile home park supply is limited to nominal 120/240-V, single-phase, 3-wire to accommodate appliances rated at nominal 240 V or a combination nominal voltage of 120/240 V. Accordingly, a 3-wire 120/208-V supply, derived from a 4-wire 208Y/120-V supply, would not be acceptable.
550.31. Allowable Demand Factors. While the demand factor for a single mobile home lot is computed at 16,000 VA (unless the 550.18 result for the typical home provided results in a larger number), it should be noted that 550.32(B) requires the feeder circuit conductors extending to each mobile home lot to be not less than 100 A. Table 550.31 provides demand factors for a mobile home lot with multiple units connected to a common service or feeder.
550.32. Mobile Home Service Equipment. The service equipment disconnect means for a mobile home must be mounted with the bottom of its enclosure at least 600 mm (2 ft) above the ground, because some very low mounted disconnects are subject to flooding and are difficult to operate. But the disconnect must not be higher than 2.0 m (6 ft 7 in.) above the ground or platform (Fig. 550-3). For mobile homes that are actually mobile and not mounted on a permanent foundation as covered in Part (B) of this section, the service equipment must not be placed on the home, and the final connection must be through a feeder as covered in 550.33. Part (B) covers what has become the more usual condition, where the home is located on a permanent foundation with no intention of relocation. Note the requirement in (7) for a red warning label advising site electricians not to make service connections until a grounding electrode is installed and connected properly.
Fig. 550-3. Mobile home service disconnect must comply with minimum mounting height rule. (Sec. 550.32.)
551.1. Scope. Some states have laws that require factory inspection of recreational vehicles by state inspectors. Such laws closely follow NFPA 1192-2008, Standard for Recreational Vehicles. This standard contains electrical requirements in accordance with part (I) of Art. 551. It also contains requirements for plumbing and heating systems.
551.10. Low-Voltage Systems. This section concerns 12-V systems for running and signal lights similar to those in conventional automobile systems. Also, many recreational vehicles use 12-V systems for interior lighting or other small loads. The 12-V system is derived from an onboard battery or through a transfer switch from a 120/12-V transformer often equipped with a full-wave rectifier.
551.20. Combination Electrical Systems. As explained in the last exception of part (B), “momentarily” operated electric appliances do not affect converter sizing. This exception excludes from calculation of the required converter rating any appliance that operates only momentarily (by a momentary contact switch) and cannot have its switch left in the closed position. Such appliances draw current for only momentary periods and do not have to be counted as load in sizing the converter rating.
551.42. Branch Circuits Required. This rule coordinates the rules on branch circuits to those of 551.45 on distribution panelboard. Note that if the branch circuits exceed five, the minimum supply becomes 50 A from a 120/240-V source (or 208 V, reflecting the allowance for three-phase distributions in RV parks).
551.45. Distribution Panelboard. Note that Part (B) amends the normal workspace distances, reducing the width from 752 mm (30 in.) to 600 mm (24 in.) and the depth from 914 mm (3 ft) to 750 mm (30 in.). The metric differences between the two 30-in. spacings constitute another amendment, because unlike 110.26, this section uses hard conversions throughout (see 90.9 for more information on this topic). In addition, this section does not require the dimensions to be applied before the RV is set up. This allows for panels in “side-out” RVs to be obstructed during travel, provided the proper clearances are provided when the vehicle is fully expanded on site.
551.46. Means for Connecting to Power Supply. Note that the configuration of the 125-V 30-A, 2-pole 3-wire grounding plug and receptacle is unique to the RV industry, and is incompatible with the standard NEMA 5-30 configuration for this voltage, amperage, and number of poles. Part (E) correlates with 551.77, assuring that properly configured RVs can park at properly configured RV parks with a minimum of cord travel.
551.47. Wiring Methods. RV wiring is chiefly of interest to their manufacturers and will not be considered at length here. For just one of many examples in a long section, Part (P) covers the rules for wiring side-out provisions (previously mentioned here at 551.45).
551.71. Type Receptacles Provided. RV parks must meet certain minimum receptacle allotments, which in turn have a bearing on the number of sites that will go into the load calculations to determine the overall service size for the park. To begin with, every site with an electrical supply must have a 20-A 125-V two-pole 3-wire grounding receptacle outlet. The next issue is 125/250-V, 50-A 3-pole 4-wire grounding receptacle outlets, for which at least one-fifth (20 percent) of the sites with electric power must be configured. The next step is to consider the 30-A 125-V 2-pole 3-wire grounding receptacle, for which at least 70 percent of the sites must have this configuration. The remainder of the sites are not specified, but it is permissible to install multiple configurations on any site. The load for a site is simply based on the highest receptacle rating installed. Note that dedicated tent sites can be excluded when figuring the number of 125/250-V 50-A receptacles and the number of 125-V 30-A receptacles.
551.73. Calculated Load. The load on a site is based on the highest rated receptacle. For 50-A sites, use 9600 VA; for 30-A sites, use 3600 VA; for 20-A sites, use 2400 VA; and for the dedicated tent sites with a 20-A 125-V receptacle use 600 VA. Add the results together and then apply the demand factor from Table 551.73 that matches the total numbered of powered sites. If one powered location can serve two vehicles, use the two highest rated receptacles in the summation.
551.77. Recreational Vehicle Site Supply Equipment. This is where to find how to place the equipment, which differs, based on whether or not the site is a pull-through site.
552.2Definition. A park trailer is a unit that is built on a single chassis mounted on wheels and has a gross trailer area not exceeding 37 m2 (400 ft2) in the set-up mode. The article has no independent provisions or demand factors for the placement of these units in a group, although 552.47 does have a procedure for determining the rated load of any given unit. These calculations, as in the case of many other provisions in this part of the article, parallel comparable requirements for both mobile homes and for recreational vehicles. Here again, there are no requirements in this article that interface the loads in these units with other loads in the location where they are connected. For example, if a park trailer is set up at an RV park, how does its load relate to Table 551.73? Absent any demand factor allowances, and there are none, it must be taken at 100 percent. In addition, there are no rules for the feeder supply to the trailers, leaving open the question of whether direct connections are required or whether cord connections are permitted.
553.1. Scope. This article covers the electrical system in a building—either residential (dwelling unit) or nonresidential—that floats on water, is moored in a permanent location, and has its electrical system supplied from a supply system on land. The rules apply to any floating building and are not limited only to floating “dwelling units.”
553.4. Location of Service Equipment. The service-disconnect means and protection for a floating building must not be mounted on the unit. This ensures the ability to disconnect the supply conductors to the floating building in an emergency, such as in a storm, in the event that it is necessary to move the unit quickly (Fig. 553-1).
Fig. 553-1. Service equipment for a floating building must be on the dock, pier, or wharf.
553.7. Installation of Services and Feeders. For obvious reasons the wiring between land and the floating building must be flexible, and this section makes that clear in (A). Although flexible raceways are permitted, extra hard usage flexible portable power cable with it fine conductor stranding is the most resilient. Such cord must be marked “sunlight-resistant” and for “wet locations.” If cord is used, however, the stranding will not terminate correctly in conventional mechanical lugs. According to UL data, a termination for that type of stranding must use a lug marked with the class of stranding and the number of strands, and generally only a few hydraulically crimped lugs will be available for this purpose.
553.8. General Requirements. A green-colored, insulated equipment grounding conductor must be used in a feeder to the main panel of a floating building. For conductors larger than 6 AWG, the color can be applied afterward in accordance with the usual rules in 250.119. This equipment grounding conductor must be run to the panel from an equipment grounding terminal (or bonded neutral bus) in the building’s service equipment on land.
555.1. Scope. This article covers both fixed and floating piers, wharfs, and docks—as in boat basins or marinas. In Fig. 555-1, branch circuits and feeder cables run from panelboards in the electrical shed at the left, down, and underground into a fabricated cable space running the length of the pier shown at the right, supplying shore-power receptacle pedestals (arrows) along both sides of the pier.
555.2. Definitions. The “electrical datum plane” is a horizontal plane that serves as the reference level for any rules governing height above water level. It is absolutely essential that this be determined before proceeding with other requirements. It is 606 mm (2 ft) above normal high water, except that on a floating pier, it is 762 mm (30 in.) above the water and also 305 mm (12 in.) above the floating pier.
Fig. 555-1. This is one part of a 406-boat marina where shore power is supplied to moored boats from receptacle power pedestals (arrows) supplied by cables run under the pier from a panelboard in the shed at the left. (Sec. 555.1.)
555.7. Location of Service Equipment. As in the case of floating buildings, service equipment must remain on shore where floating docks or other facilities are supplied.
555.9. Electrical Connections. All connections must be at least 305 mm (1 ft) above a fixed or floating pier, and simultaneously above the datum plane. For a floating piers, however, connections using sealed methods identified for submersion are permitted provided they are enclosed in approved junction boxes.
555.12. Load Calculations for Service and Feeder Conductors. This is an unusual load calculation in that it is entirely based on the current ratings of the power receptacles installed for each slip. If two (or more) receptacles are provided at a slip, the one whose configuration translates into the largest kVA load profile is the one used to enter the table. If the slips have kilowatt-hour meters, a reduction in electrical demand of 10 percent is assumed (through the use of a 0.9 multiplier). Note that on the literal text, the meters need not be read or used to bill the boat owners in order to achieve this presumed reduction in load. In addition, the neutrals must not be further reduced under the terms of 220.61(B); this demand factor table is the only permitted calculation for all circuit conductors.
555.13. Wiring Methods and Installation. The rules here present various options that are available for the circuiting to the loads at marinas and boatyards. This section recognizes any wiring method “identified” for use in wet locations. Examples of wiring methods that are recognized by the NEC for use in wet locations are as follows:
1. Rigid nonmetallic conduit.
2. Type MI cable.
3. Type UF cable.
4. Corrosion-resistant rigid metal conduit—which is taken to mean either rigid aluminum conduit or galvanized rigid steel conduit. The use of the word corrosion-resistant is not intended to require a plastic jacket on galvanized rigid steel conduit, although such a jacket does provide significantly better resistance to natural corrosion, such as rusting.
5. Galvanized IMC.
6. Type MC (metal-clad) cable.
7. Extra-hard usage portable power cable, such as Type W, where listed for both wet locations and sunlight resistance, has tremendous ability to flex because of its fine stranding. Take care to observe the UL termination limitations on fine-stranding at terminations, as previously covered above on floating buildings on the same wire.
In the design and construction of a marina it is usually necessary to compare the material and labor costs involved in each of those methods. Emphasis is generally placed on long, reliable life of the wiring system—with high resistance to corrosion as well as high mechanical strength to withstand impact and to accommodate some flexing in the circuit runs. The need for great flexibility in running the circuits under the pier and coming up to receptacle pedestals and lighting poles is often extremely important in routing the circuits over, around, and below the many obstructions commonly built into pier construction. And that concern for flexibility in routing can weigh heavily as a labor cost if a rigid conduit system is used.
Any of the recognized types of cable offer the material-labor advantage of a preassembled, highly flexible “raceway and conductor” makeup that is pretested and especially suited to the bends, offsets, and saddles in the circuit routing at piers, as shown in Fig. 555-2. Cable with a metal armor can offer a completely sealed sheath over the conductors, impervious to fluids and water. For added protection for the metal jacket against oils and other corrosive agents, the cable assembly can have an overall PVC jacket.
555.15. Grounding. The purpose is to require an insulated equipment grounding wire that will ensure a grounding circuit of high integrity. Because of the corrosive influences around marinas and boatyards, metal raceways and boxes are not permitted to serve as equipment grounding conductors.
555.19. Receptacles. Figure 555-3 shows typical configurations of locking-and grounding-type receptacles and attachment plugs used in marinas and boatyards. A complete chart of these devices can be obtained from the National Electrical Manufacturers Association or wiring-device manufacturers. Locking-type receptacles and caps are required to provide proper contact and assurance that attachment plugs will not fall out easily and disconnect onboard equipment such as bilge pumps or refrigerators. Shore-power receptacles for boats must be rated at least 30 A.
Fig. 555-2. PVC-jacketed metal-clad cable—with a continuous, corrugated aluminum armor that is completely impervious to any moisture and water and resistant to corrosive agents—is used for branch circuits and feeders under this marina pier. (Sec. 555.13.)
Fig. 555-3. These types of connections provide shore power for boats. (Sec. 555.19.)
As covered in part (A)(3), each single receptacle must be installed on an individual or multiwire branch circuit, with only the one receptacle on the circuit. As shown in Fig. 555-4, a receptacle pedestal unit (two mounted back to back at each location) contains receptacles providing plug-in power to boats at their berths along the pier, with CB protection and control in each housing. As required by NEC 555.19, each receptacle must be rated not less than 30 A and must be a single locking- and grounding-type receptacle. There is no requirement for ground-fault circuit interruption on these receptacles. (However, at a marina, any 15- or 20-A, 120-V receptacles that are not used for shore power to boats must be provided with GFCI protection.)
Fig. 555-4. Receptacle providing shore power to each boat is contained in a “power pedestal” and is a locking and grounding type. (Sec. 555.19.)
Also, as required by NEC 555.19(A)(3), each individual receptacle in the pedestal unit is supplied by a separate branch circuit of the voltage and current rating that corresponds to the receptacle rating. At each pedestal location, a separate bare, stranded No. 6 copper conductor (arrow) is available as a static grounding conductor bonded to all pedestals and lighting fixtures. The inset in Fig. 555-4 shows one receptacle wiring arrangement. Hookup details at pedestal units vary with voltage ratings, current ratings, and phase configuration of power required by different sizes of boats—from small motorboats up to 100-ft yachts. Note also that each shore power receptacle must be wired in conjunction with a properly marked disconnecting means not over 762 mm (30 in.) away, as covered in 555.17.
555.21. Motor Fuel Dispensing Stations—Hazardous (Classified) Locations. Figure 555-5 shows the rules that define the need for hazardous location wiring at a marina. A fuel-dispensing area at the end of the pier consists of gasoline and diesel fuel pumps at the pier edge, with a shack for service personnel at the right (arrow). A panel installed in the shack supplies lighting and receptacles in the shack, as well as the outdoor sign and pumps in the fuel dispensers. Electrical connections from the dispenser pumps tie into the panel. The inset shows the limits and classifications of hazardous locations around each gasoline-dispensing pump. As indicated, some of the space is classified as Class I, Division 1, and other space as Class I, Division 2—both Group D, gasoline.
Fig. 555-5. Gasoline pumping areas at a marina must utilize Class I wiring and equipment within the specific classified boundaries. (Sec. 555.21.)
Type MC cable is suited for use in the Division 2 spaces, but only threaded metal conduit or Type MI cable is suited for the Division 1 spaces.
555.22. Repair Facilities—Hazardous (Classified Locations). This is the key to bringing Art. 511 requirements to bear on motorboats being serviced at a dry dock or comparable facility.
590.1. Scope. Although a temporary electrical system does not have to be made up with the detail and relative permanence that characterizes a so-called permanent wiring system, the specific rules of this article cover the only permissible ways in which a temporary wiring system may differ from a permanent system. Aside from the given permissions for variation from rules on permanent wiring, all temporary systems are required to comply in all other respects with Code rules covering permanent wiring (Fig. 590-1).
Fig. 590-1. Temporary wiring is not an “anything goes” condition and must comply with standard Code rules to prevent a rat-nest condition which can pose hazard to life and property. (Sec. 590.1.)
590.3. Time Constraints. In part (A), the words maintenance and repair indicate that the less rigorous methods of temporary wiring may be used and that all rules on temporary wiring must be observed wherever maintenance or repair work is in progress. This expands the applicability of temporary wiring beyond new construction, remodeling work, or demolition.
Part (B) recognizes use of temporary wiring for seasonal or holiday displays and decorations, as shown in Fig. 590-2.
Fig. 590-2. Temporary wiring techniques are permitted for 90 days for such “experimental” work as energy demand analysis. (Sec. 590.3.)
Part (C) of this section permits temporary wiring to be used for other than simple construction work. Such wiring, as covered in this article, may also be used during emergency conditions or for testing, experiments, or development activities. As the proposal for this Code rule noted:
Were it not permissible to use temporary wiring methods for testing purposes, it would be impossible to check, before placing in service, many electrical installations. Likewise, emergency conditions would remain without electric power and lighting until permanent installation could be made.
However, part (D) of this section is aimed at ensuring that the equipment and circuits installed under this article are really temporary and not a backdoor to low-quality permanent wiring systems.
590.4. General. Although part (A) requires a temporary service to satisfy all the rules of Art. 230, part (B) recognizes the use of temporary feeders that are conductor “cable assemblies” used as open wiring (Fig. 590-3), multiconductor cable assemblies (Type NM, UF, etc.), or multiconductor cord or cable of the type covered by Art. 400 for hard-usage or extra-hard-usage flexible cords and cables, which are not acceptable for use as feeder or branch-circuit conductors of permanent wiring systems. 400.8 specifically prohibits the use of such cords and cables “as a substitute for the fixed wiring of a structure.” As shown in Fig. 590-4, prewired portable cables with plug and socket assemblies are available for power risers in conjunction with GFCI-protected branch-circuit centers, or cables can be run horizontally on a single floor to suit needs. GFCI breakers may be used in temporary panelboards interconnected with cable and feeding standard receptacles in portable boxes, as shown in Fig. 590-5.
590.4(C) requires temporary branch circuits to consist of multiconductor cable assemblies (Types NM and UF) or cords or cables covered in Table 400-4, provided that they originate in a panelboard or “an approved power outlet,” which is one of the manufactured assemblies made for job site temporary wiring. As shown in Fig. 590-6, the temporary branch circuits for receptacle outlets may be part of a manufactured temporary system, which consists of cable harnesses and power centers (or outlets). Several variations of protection may be provided by such portable receptacle boxes, as shown in Fig. 590-6. Box 1 may have GFCI protection for its own receptacles without providing downstream protection. Box 2 may have the same protection as box 1 and in addition have GFCI protection for its 50-A outlet, thus providing protection for box 3. With this arrangement, box 1 will sense the ground fault from the worker at upper left and will trip, allowing boxes 2 and 3 to continue to provide power. Or all three boxes could receive GFCI protection from a permanently mounted loadcenter feeding the 50-A receptacle outlet at upper left. In this case, the ground fault shown would interrupt the power to all boxes. It should be noted that use of a GFCI breaker may be viewed as a violation for temporary power applications because it does not have the same characteristics—that is, “open neutral” and “reverse phasing” protection—as do listed temporary power GFCI devices.
Fig. 590-3. The exception to 527.4(B) permits temporary feeders to be run as open individual conductors supported by insulators spaced not over 10 ft (3.0 m) apart where used during emergencies or testing. (Sec. 590.4.)
Fig. 590-4. Temporary feeders may be cord assemblies made especially for such use. (Sec. 590.4.)
Fig. 590-5. Distribution for temporary power may utilize cable or raceway feeders. (Sec. 590.4.)
Fig. 590-6. Temporary branch circuits may be part of a manufactured system. (Sec. 590.4.)
590.6 makes it clear that only receptacles used under temporary job conditions require GFCI protection. The implication is that the nonmetallic-sheathed cable runs and pigtail connections traditionally associated with temporary power on the job site would not win awards for neatness and safety, but that once the permanent feeders and panelboards are in place and energized, the shock hazard is considerably reduced.
However, as long as portable tools are being used in damp locations in close proximity with grounded building steel and other conductive surfaces, the possibility of shock exists from faulty equipment whether it is energized from temporary or from permanent circuits.
Standard panelboards used for temporary power fitted with GFCI circuit breakers for the protection of entire circuits satisfies the rules of 590.6, but may be a violation of 110.3(B) because breaker type GFCI devices listed for permanent installation would not satisfy the UL requirements for temporary power use. However, the many varieties of portable power distribution centers and modules have been developed with integral GFCI breakers protecting single-phase, 15- and 20-A, 120-V circuits. Other circuits (higher amperage, higher voltage, and 3-phase) are also required by the NE Code to have GFCI protection, or the Assured Equipment Grounding Conductor Program, described in 590.6(B), may be used. A variety of cord sets are also available for use with GFCI-protected plug-in units to supply temporary lighting and receptacle outlets.
While a manufactured system of cable harnesses and power-outlet centers costs more than nonmetallic-sheathed cable runs and pigtail sockets, it is completely recoverable, and its cost can be written off over several jobs. From then on, with the exception of costs for setup and removal, storage, and transportation, much of the temporary power charges included in bids could be profit.
In previous Code editions, part (C) of this section required temporary wiring circuits to be “fastened at ceiling height every 10 ft (3.0 m).” But now, if such circuits operate at not over 150 V to ground and are not subject to physical damage, the fourth sentence in this paragraph permits open-wiring temporary branch circuits to be run at any height “supported on insulators at intervals of not more than 10 ft (3.0 m)” where used for other than “during the period of construction” as covered in part (A) of 590.3. Open wiring must not be laid on the floor or ground.
In the interest of greater safety, part (D) prohibits the use of both receptacles and lighting on the same temporary branch circuit on construction sites. The purpose is to provide complete separation of the lighting so that operation of an overcurrent device or a GFCI due to a fault or overload of cord-connected tools will not simultaneously disconnect lighting (Fig. 590-7).
According to part (E), every multiwire branch circuit must have a disconnect means that simultaneously opens all ungrounded wires of the temporary circuit. At the power outlet or panelboard supplying any temporary multiwire branch circuit (two hot legs and neutral, or three hot legs and neutral), a multi-pole disconnect means must be used. Either a 2-pole or a 3-pole switch or circuit breaker would satisfy the rule, or single-pole switches of single-pole CBs may be used with approved handle ties to permit the single-pole devices to operate together (simultaneously) for each multiwire circuit, as shown for the multiwire lighting circuit in Fig. 590-7.
Part (F) requires lamps for general lighting on temporary wiring systems to be “protected from accidental contact or breakage.” Protection must be provided by a suitable fixture or lampholder with a guard (Fig. 590-8). OSHA rules also require the use of a suitable metal or plastic guard on each lamp. As shown in Fig. 590-9, commercial lighting strings provide illumination where required. Splice enclosure is equipped with integral support means, and a variety of lamp-guard styles provide protection for lamp bulbs.
Part (F) requires grounding of metal lamp sockets. The high level of exposure to shock hazard on construction sites makes use of ungrounded metal-shell sockets extremely hazardous. When they are used, the shell must be grounded by a conductor run with the temporary circuit.
Fig. 590-7. This rule prevents loss of lighting when a defective, high-leakage, or overloaded Code-connected tool or appliance opens the branch-circuit protection of a circuit supplying one or more receptacles. (Sec. 590.4.)
In part (G), splices or tap-offs are permitted to be made in temporary wiring circuits of cord or cable without the use of a junction box or other enclosure at the point of splice or tap (Fig. 590-10). But this new permission applies only to nonmetallic cords and cables. A box, conduit body, or terminal fitting must be used when a change is made from a cord or cable circuit to a raceway system or to a metal-clad or metal-sheathed cable.
Fig. 590-8. A lampholder with a guard is proper protection for a lamp at any height in a temporary wiring system (above). Unguarded lamps at any height constitute a Code violation (right). (Sec. 590.4.)
Fig. 590-9. Temporary lighting strings of cable and sockets are available from manufacturers. Note the multiconductor cable makeup; festoon lighting strings are not permitted. (Sec. 590.4.)
Fig. 590-10. Splices may be used without boxes for cord and cable runs on construction sites. (Sec. 590.4.)
Regulations in part (H) require protection of flexible cords and cables from damage due to pinching, abrasion, cutting, or other abuse.
Part (I) calls for the use of proper fittings to secure cables that enter enclosures containing receptacles and/or switches.
Part (J) requires cable assemblies and cords to be supported at intervals that assure protection from physical damage. You can use staples, cable ties, straps, or other fittings that don’t damage the cable. The idea here is to allow a greater support interval than would be covered in the applicable article, since this is just for temporary applications. Vegetation, however, is prohibited from being used as temporary support of overhead runs of branch circuit or feeder conductors. The only exception is holiday decorative lighting, which is permitted to run from tree to tree provided there is some tension take-up mechanism or other approved arrangement that will prevent tree movement from damaging the temporary lighting strings.
590.5. Listing of Decorative Lighting. Here the Code makes it absolutely clear that any manufactured decorative lighting used for temporary installation must be listed. And this would include a proper listing for the application. That is, where used outdoors such lighting must also be listed for outdoor use or wet locations, etc. Note that 410.160 imposes the identical requirement.
590.6. Ground-Fault Protection for Personnel. This section covers the rules that concern GFCI protection for all receptacles supplied from temporary wiring systems.
The basic rule of part (A) of this section says that ground-fault circuit interrupters (of the type listed for use in temporary power applications—not GFCI circuit breakers or GFCI receptacles listed for permanent use in dwellings or at pools) must be used to provide personnel protection for all receptacles of the designated rating that “are not part of the permanent wiring of the building or structure” (Fig. 590-11). In addition, the second sentence mandates GFCI protection for all permanently installed receptacles—it’s presumed that this applies only to 15-, 20-, and 30-A 125-V receptacles, but this is not clear—that are used for temporary power (Fig. 590-12).
Fig. 590-11. GFCI protection on construction sites for receptacles in use. (Sec. 590.6.)
Fig. 590-12. Two ways to satisfy the basic rule on personnel shock protection at temporary receptacles on construction sites. (Sec. 590.6.) Such devices must be “identified for portable use.” That means they will have internal circuitry that opens all poles of the device if the grounded circuit conductor is open for any reason. Conventional GFCI devices for permanent connection in a panel or at an outlet do not have this feature, and will fail closed (energized) if the grounded conductor opens because their circuitry will not have the 120 V they need to work. This is why making a short extension cord with an ordinary GFCI receptacle in a box does not comply with this requirement.
But one sentence in the Code rule significantly qualifies the need for GFCI protection of the designated receptacle outlets:
GFCI protection is required only for those receptacles that “are in use by personnel.”
This sentence clearly limits required GFCI protection to receptacles that are actually being used at any particular time. Receptacles not in use do not have to be GFCI-protected. This means that portable GFCI protectors may be used at only those outlets being used (Fig. 590-13). There is no need to use GFCI breakers in the panel to protect all receptacles or to use all GFCI-type receptacles; the last sentence of 590.6(A) says as much. This seems to seriously confuse the task of electrical inspection: If all cord-connected tools and appliances are unplugged from receptacles when the inspector comes on the job, then none of the receptacles is “in use” and none of them has to have GFCI protection, and there is no Code violation. Most inspectors can see through such foolishness.
Fig. 590-13. Portable GFCI devices may be used to satisfy GFCI rule. (Sec. 590.6.)
A new requirement given in part (B) extends the GFCI requirements to all receptacles “other than 125-V, single-phase, 15-, 20-, and 30-A” receptacles. That includes 3-phase and phase-to-phase receptacles of any current value temporarily installed. Alternately, the Assured Equipment Grounding Program explained in the remainder of this section may be used, or cord sets with integral GFCI protection may be used.
Although there are products available with cut sheets that hint they are GFCIs for 480Y/277-V systems, etc., they are not. There are no such listings. A product with an equivalent capability to provide electric shock protection at such a higher voltage would require an entirely different response time and a different current trip setting, perhaps 3 mA for a 277-V to ground system. No such standards exist, no listings exist, and there does not seem to be any likelihood that this situation will change. One issue is that when you get down to a low enough level to be effective at the higher voltage, you probably have a product that will frequently nuisance trip. The bottom line is that the requirement in (6)(B), at least insofar as higher voltages are concerned, is in effect a mandate to use AEGCP. There simply is no other alternative.
Still another option for avoiding use of GFCI protection on temporary wiring systems is given in part (B) of this section for other than 15-, 20-, or 30-A, 125-V receptacles. GFCI protection at the higher ampere and voltage ratings of receptacles may be omitted totally if a “written procedure” is established to assure testing and maintenance of “equipment grounding conductors” for receptacles, cord sets, and cord- and plug-connected tools and appliances used on the temporary wiring systems (Fig. 590-14). In effect, the NE Code accepts such an equipment grounding conductor program as a measure that provides safety that is equivalent to the safety afforded by GFCI protection. GFCI protection is not required for other than the 15-, 20-, and 30-A, 125-V receptacles if all the following conditions are satisfied:
1. The inspection authority having jurisdiction over a construction site must approve a written procedure for an equipment grounding program.
2. The program must be enforced by a single designated person at the construction site.
3. “Electrical continuity” tests must be conducted on all equipment grounding conductors and their connections. The requirements on making such tests are vague, but they do call for:
a. Testing of fixed receptacles where there is any evidence of damage.
b. Testing of extension cords before they are first used and again where there is evidence of damage or after repairs have been made on such cords.
c. Testing of all tools, appliances, and other equipment that connect by cord and plug before they are first used on a construction site, again any time there is any evidence of damage, after any repair, and at least every 3 months.
Fig. 590-14. Assured grounding program eliminates the need for GFCI. Note: The assured equipment grounding program may only be used on 15-, 20-, and 30-A, 125-V receptacles in industrial establishments. (Sec. 590.6.)
Obviously, these rules are very general and could be satisfied in either a rigorous, detailed manner or a fast, simple way that barely meets the qualitative criteria. The electrical contractor who has responsibility for the temporary wiring on any job site is the one to develop, write, and supervise the Assured Equipment Grounding Program, where that option is chosen as an alternative to use of GFCI protection. This whole NE Code approach to use of either GFCI or an Assured Equipment Grounding Program directly parallels the new OSHA approach to the matter of receptacle protection on construction sites.
It should be noted that the Assured Equipment Grounding Program described in part (B) is one of the most frequently cited violations during OSHA inspections. Implementation is a bureaucratic nightmare and is rarely successfully executed.
