How does electricity get from the generating plant to your town, your neighborhood, and your house? You might wonder about that, the next time you have a local or regional power failure! You should also know which fuses or breakers affect which circuits and appliances inside your home or business. That knowledge can help you avoid overloading circuits, and to figure out how many devices or appliances you can safely use in a single outlet or circuit. If you travel to another country, can you use your cell-phone charger, your notebook computer, or your electric hair dryer there? You’ll have a happier trip if you find out before you destroy something, not afterwards!
Electrical energy morphs multiple times from birth to demise. Nevertheless, the initial source always exists as kinetic energy in some nonelectrical form, such as falling or flowing water (hydroelectric), coal or oil or methane gas (“fossil fuels”), radioactive substances (nuclear), moving air (wind), light from the sun (solar), or heat from the earth’s interior (geothermal).
In fossil-fuel, nuclear, geothermal, and some solar electric generating systems, heat boils water to make steam that passes through turbines under high pressure. The turbines drive massive electric generators. As the power demand increases, it takes more and more force to turn a generator shaft. That’s why the utility companies need so much oil, coal, or gas to run a fossil-fuel power plant. Nuclear energy systems pretty much get rid of the fuel supply conundrum, but they produce radioactive waste that brings a whole new set of problems. Wind, solar, and geothermal power plants produce no waste or pollution when they operate, except for a little bit of residual heat energy. Hydrogen fusion power plants, if and when engineers manage to deploy them, will produce no waste other than heat and water vapor.
In a hydroelectric power plant, waterfalls, tides, or river currents directly drive specialized turbines that turn the generator shafts. In a wind-driven system, moving air operates devices similar to windmills, producing torque that turns the generator shafts. Although these types of power plants do not pollute the environment directly, they nevertheless present problems. The construction of a large hydroelectric dam can disrupt ecosystems, adversely affect agricultural and economic interests downriver, and displace people upriver by flooding their land. Many people regard arrays of windmill-like structures as an eyesore, but in order to generate significant electrical power, many such devices must be connected together and operated simultaneously. If you’ve ever driven past a large “wind ranch,” you know that wind turbines can dominate the landscape.
In a photovoltaic (PV) energy generating system, semiconductor devices convert sunlight directly into DC electricity at low voltage. This DC must undergo conversion to high-voltage AC for transmission and distribution. The PV cells can’t collect any energy during the hours of darkness, so storage batteries are necessary if a stand-alone PV system is to provide useful energy at night. Photovoltaics without storage batteries can work in conjunction with existing utilities to supplement the total energy supply available to all consumers in a power grid. A “solar ranch” has a lower profile than a “wind ranch,” a feature that some people appreciate, especially those who live in the vicinity where wind turbines can ruin their views of the countryside.
When electric current travels along wires over great distances, some power goes to waste because of the wire resistance. This phenomenon cannot be avoided. No wire forms a perfect conductor, so we always end up losing some power in transmission lines because of “electrical drag.” Engineers do their best to minimize this power loss. Two measures are commonly employed to that end.
First, engineers try to keep the wire resistance to a minimum by using large-diameter wires made from metal having excellent conductivity, and by routing the power lines in such a way as to keep their spans as short as possible. This approach can be carried out only to a certain extent in practice before physical and financial limitations “put a lid on it.” No one wants to see a high-voltage utility line run right through a residential neighborhood in their town. Mountains, canyons, and lakes present a direct physical challenge.
Second, engineers use the highest possible voltage in a long-distance transmission line. Given a constant power demand, the current goes down as the voltage goes up. The wasted power in the line varies according to the square of the current, so maximizing the voltage will minimize the power loss. These high voltages are common in cross-country high-tension (high-voltage) power lines.
High-voltage electricity, despite its advantages for long-distance transmission, would never work in your house. It would instantly destroy your appliances, it would create a fire risk, and electrical arcs, like miniature lightning bolts, would kill you before you could put a plug into an outlet.
Step-down transformers reduce the voltage of high-tension transmission lines down to a few thousand volts for distribution within municipalities. These transformers are physically large (about the size of a big car or small truck) because they must carry significant power. Several of them might be placed in a building or a fenced-off area. The outputs of these transformers feed local power lines that run along city streets.
Smaller transformers, usually mounted on utility poles or underground, step the municipal voltage down to 234 V for distribution to individual homes and businesses. These transformers are about the size of a trash barrel. Some utility outlets are supplied directly with 234 V. Large appliances, such as electric stoves, ovens, and laundry machines, commonly work at this voltage. In the United States and many other countries, smaller wall outlets and light fixtures receive single-phase electricity at 117 V.
Once the utility voltage has been stepped down to a level that won’t zap everything in your home or business, the electricity is ready to be tailored for end use. Part of that process involves separating out the different phases of current. Phase is a fancy term that refers to points along an AC wave cycle. Phase can also express the extent of the timing difference between two AC waves that have the same frequency.
You can specify time points in an AC wave by dividing one complete cycle into 360 equal parts called degrees or degrees of phase. Assign 0 degrees (0°) to the point in the cycle where the wave crosses the time axis going upward (with the voltage getting more positive). Then:
• One-quarter of the way through the cycle equals 90°
• Halfway through equals 180°
• Three-quarters of the way through equals 270°
• The end of the cycle equals 360°
Figure 3-1 illustrates this concept for a sine wave of the sort that you’ll find at a household utility outlet. If you have trouble with the idea of dividing a wave into 360 degrees, imagine each cycle of the wave as a complete trip around a perfect circle. Then you can simply take advantage of a paradigm with which we’re all familiar:
FIGURE 3-1 Degrees of phase tell you how much of a wave cycle has passed since its starting time. You can think of one complete wave cycle as going exactly once around a full circle.
• One-quarter of the way around a circle equals 90°
• Halfway around equals 180°
• Three-quarters of the way around equals 270°
• Exactly once around equals 360°
The term phase coincidence means that two waves with the same frequency begin at the same instant in time. If the waveforms have identical shapes (but maybe different voltages), they follow each other along from instant to instant. Figure 3-2 shows an example of phase coincidence between two perfect sine waves whose voltages differ. The phase difference, also called the phase angle, equals 0°. In this kind of situation, you always know several things:
FIGURE 3-2 Here’s a graph of sine waves in phase coincidence; the phase difference in this case equals 0°. The two waves follow right along with each other.
• The positive peak voltage of the resultant wave, which is also a sine wave, equals the sum of the positive peak voltages of the two composite waves.
• The negative peak voltage of the resultant wave equals the sum of the negative peak voltages of the composite waves.
• The peak-to-peak voltage of the resultant wave equals the sum of the peak-to-peak voltages of the composite waves.
• The phase of the resultant wave coincides with the phases of the two composite waves.
Two perfect sine waves having the same frequency can differ in phase by any amount from 0° (phase coincidence), through 90° (phase quadrature, meaning a difference of 1/4 of a cycle), through 180° (a difference of half a cycle), through 270° (phase quadrature again, but a difference of 3/4 of a cycle), and finally 360° (phase coincidence, but offset by a full cycle).
When two pure sine waves of identical frequency begin exactly half a cycle apart in time, engineers say that they occur 180° out of phase with respect to each other. Figure 3-3 illustrates a situation of this sort.
FIGURE 3-3 Here’s a graph of sine waves that differ in phase by 180° (half a cycle).
If two perfect sine waves have identical voltages and occur 180° out of phase, then they cancel each other out. The voltages of the two waves are equal and opposite at every point in time, so they always add up to zero! If two perfect sine waves have different voltages and occur 180° out of phase, then:
• The peak-to-peak voltage of the resultant wave, which is also a sine wave, equals the difference between the peak-to-peak voltages of the two composites.
• The phase of the resultant wave coincides with the phase of the stronger of the two composite waves.
Single-phase AC consists of a single, pure sine wave. You’ll find this sort of AC at standard wall outlets intended for small appliances, such as lamps, TV sets, and computers. In most parts of the United States, the voltage is standardized at 117 V RMS for single-phase AC, but it can vary a few percentage points above or below this level, depending on the overall utility power demand at the time, your location, and the whims of your local electric power provider.
Over long-distance power lines, utility companies transmit electricity in the form of three sine waves, each having the same RMS voltage, but differing in relative phase by 120° (1/3 of a cycle). Engineers call it three-phase AC. Each sine wave travels along its own wire, so the transmission line has three wires (or pairs of wires to minimize resistance losses). In addition, a well-designed transmission line always has a single wire connected to a good electrical ground, placed above the current-carrying lines. This grounded wire serves to “attract lightning away” from the power lines. Lightning behaves in unpredictable ways, but it tends to strike objects connected to a good electrical ground, and it also tends to strike the highest or tallest thing in the vicinity.
Figure 3-4 shows three-phase AC as a graph of voltage versus time. The three individual waves are called phase 1, phase 2, and phase 3. The horizontal axis increases in degrees of phase as you go from left to right, based on the start of the wave for phase 1 (shown as a solid curve) where the voltage equals zero and increases positively. Phase 2 (shown as a dashed curve) comes 1/3 of a cycle later than Phase 1, and phase 3 (shown as a dotted curve) comes 2/3 of a cycle later than phase 1. Therefore, phase 2 starts its cycle 120° later than phase 1 starts, and phase 3 starts its cycle 120° later than phase 2 starts.
FIGURE 3-4 Here’s a graph of three-phase AC. Each pure sine wave is separated by 120°, or 1/3 of a cycle, from the other two.
For residential and business service in most of the United States and Canada, you’ll find split-phase AC in common use. Two sine waves, each at 117 V RMS, travel along their own dedicated wires, with a third wire connected to electrical ground. Figure 3-5 shows a graph of the waves in this arrangement. The two phases directly oppose each other. Households can take advantage of either phase alone, along with the grounded wire, to serve 117 V RMS appliances, such as lamps, computers, and television sets. Both phases can be used together so that they buck (work against) each other, resulting in an effective voltage of 234 V RMS between them (234 V equals twice 117 V).
FIGURE 3-5 Here’s a graph of split-phase AC. The two pure sine waves are separated by 180°, or half a cycle, so they directly oppose if used together, in effect doubling the RMS voltage of either wave alone.
When you look closely at the utility wires coming into your house (assuming that they’re above ground so you can see them), you’ll probably find two black insulated wires wrapped around a single bare wire. The bare wire goes to electrical ground. The two insulated wires carry the 117 V RMS sine waves in split-phase form. Your fuse or breaker box separates the phases. Some parts of your house receive 117 V RMS from one phase; other parts of the house get 117 V RMS from the other phase. Heavy-duty appliances, such as laundry machines and electric ovens, receive both phases bucking each other along with an electrical ground, providing 234 V RMS, the effective voltage difference between the two opposing phases.
An electric meter measures the amount of energy that your household consumes in kilowatt hours over a period of time. A kilowatt hour (1 kWh) equals the amount of energy that a 1000-W (one-kilowatt or 1-kW) appliance consumes in an hour, or the equivalent of it. For example, a 100-W incandescent bulb will take 10 hours to consume 1 kWh, a 10-W compact fluorescent lamp (CFL) will take 100 hours to consume 1 kWh, and a 1-W light-emitting-diode (LED) lamp will take 1000 hours to use up 1 kWh. You can express energy as power that accumulates as time passes. Conversely, you can express power as energy consumed per unit time.
An analog mechanical electric meter employs a small motor, the speed of which depends on the current, and therefore, on the power at a constant voltage. The number of turns of the motor shaft, in a given length of time, varies in direct proportion to the number of kilowatt hours consumed. The motor connects at the point where the utility wires enter the building. That’s where the utility system splits into three circuits: one providing 234 V for heavy-duty appliances, such as the range, oven, washer, and dryer, and two others providing 117 V for small appliances, such as lamps, computers, and television sets.
If you observe one of these old-fashioned kilowatt-hour meters, you’ll see a disk spinning: sometimes fast, sometimes slowly. Its speed at any particular moment in time depends on the power that your household is using at that moment. The total number of times that the disk goes around, hour after hour, day after day during the course of each month, determines the size of the bill that you get from the power company for that month. Your bill also depends on how much the electric company charges you for each kilowatt hour that you use, of course.
An analog electric meter has several scales calibrated from 0 to 9 in circles, some going clockwise and others going counterclockwise. To read the device, you must make your “mind’s eye” go in whatever direction (clockwise or counterclockwise) the scale goes for each individual meter. Figure 3-6 shows an example. You read the dials going from left to right. In this example, the leftmost dial rotates counterclockwise, the second one goes clockwise, the third one goes counterclockwise, and the fourth one (the one on the far right) goes clockwise. For each meter scale, you can write down the number that the pointer has most recently passed. In this case those values are 3, 8, 7, and 5, so you would write 3875; and by looking closely at the far-right-hand dial, you can surmise that the meter indicates slightly more than 3875 kWh.
FIGURE 3-6 A mechanical electric meter with four rotary dials. This meter displays a total consumed energy amounting to slightly over 3875 kWh.
In some locales, electromechanical meters of the sort shown in Fig. 3-6 have been supplanted by devices that provide a direct digital readout. The simplest ones replace the rotary dial pointers with rotating cylindrical drums that have numerals printed on them. That allows you (and the meter reader) to simply write down the digits.
More sophisticated electric meters, which have proliferated in recent years, contain no moving parts. All of the mechanical components have been replaced by solid-state electronic devices and displays. Some such meters can do a lot more than simply keep track of your energy consumption. They can interconnect with supplemental systems, such as solar panels and wind turbines, allowing you to reduce your monthly electric bill, and in some cases, make a profit by selling surplus power to the electric company. Meters of this type are called smart meters.
A smart meter can register how much power (in kilowatts) you use, on the average, for specific intervals in time (usually 15 minutes) and keep a record of it. You can see the information on recent usage by watching your smart meter’s display for a minute or two. One of the readings will show a numeral followed by “kW,” which quantifies power (instead of “kWh” which quantifies energy). If you run an air conditioner, an electric oven, an electric water heater, and a refrigerator all at the same time, you’ll see a large number there. If you leave your house for a few days, shut everything down, and then look at the meter immediately when you return (and before you switch anything on again), you’ll see a small number there.
Fact or Myth?
Have you heard that smart meters can tell the power company (or the government) what appliances you use, and when you use them? Well, that’s partly true, but not completely, and in any case, it doesn’t tell you the whole story. While peak-power numbers can let the electric company know how much you consume at a maximum, those values don’t divulge what specific appliances you use, or when you use them. Theoretically, the electric company could use your smart meter to shut your house down, but they’re not likely to do that unless a dangerous event, such as a gas leak, occurs where an electrical spark could start a fire or cause an explosion. In that case, you’ll be happy that the electric company is willing and able to take measures that could save your property or even your life!
Have you ever seen a breaker box or fuse box where all the circuits have correct labels, telling you exactly which parts of the house each breaker or fuse protects? I haven’t ever come across such a thing. Even my own breaker box, which I painstakingly labeled a few years ago, still has mistakes. It’s as if gremlins lurk in the ether, waiting to sabotage our hapless attempts to create The Perfect Breaker or Fuse Box (TPBOFB).
Only one method exists that can guarantee the attainment of TPBOFB: Individually test every installed light fixture, every installed appliance, and every electrical outlet in the house against the breakers or fuses in the box. Permanent light fixtures and installed appliances, such as electric ovens, electric laundry machines, central air conditioners, and furnace fans, lend themselves easily to such tests. You need only switch them on and then open up your breakers or remove your fuses, one by one, until the relevant device goes off.
Warning! Always wear your gloves and shoes when you fiddle around with a breaker box or fuse box. You never know when the “Wicked Wizard of Watt” will try to clobber you. But he can’t hurt a well-protected person!
In the case of a permanent light fixture of the sort that you find on ceilings or exterior walls, you must make sure that the switch controlling the fixture stays on while you conduct the tests. (That rule should seem obvious, but it’s easy to forget.) Switch the light on and leave it on while you work with the breakers or fuses. Also, make sure that every permanent light fixture has a functioning bulb in it. The same rule applies for any and all wall outlets controlled by switches. Turn all such switches on, and leave them on for the duration of the test.
You can construct a simple electrical outlet tester with a light-emitting-diode (LED) lamp and a socket with a standard lamp base and two prongs that go into 117-V outlets. The best LED for this purpose is one of the sort shown in Fig. 3-7. It’s physically rugged, it will last for a long time, it’ll shine brightly enough to see in daylight but not so bright as to create a distraction, and it’s not so big that it’ll burn you when you pull it out of the socket. Screw the lamp into the plug-in socket and test it on a live outlet to make sure that it works.
FIGURE 3-7 You can assemble an outlet tester with a standard plug-in bulb socket and a light-emitting-diode (LED) lamp.
You can use your outlet tester to check any outlet within reach as you ramble between the breaker or fuse box and watch for “glow” vs. “not glow” conditions! If you’re too lazy to walk back and forth through your house dozens of times, you can employ the services of a child, spouse, or other willing person, and communicate with each other using your cell phones. Then you can carry out a variant of the famous cell-phone classic conversation: “Is it lit now?” (pause) “Is it lit now?” (pause) “Is it lit now?” and so on.
If you want to create TPBOFB (or try), you’ll have to find a blueprint of your house that shows each and every outlet and electric light fixture. Then label each outlet and fixture with the appropriate number in your breaker or fuse box. Keep a copy of that blueprint right next to the box.
Alternatively, you can make up a detailed list with two columns: full descriptions of each and every outlet and fixture in the left-hand column, and the corresponding breaker or fuse number in the right-hand column. Keep the list stored in your computer, so that you can edit it as new, never-before-known outlets appear in your house, or as outlets decide to change from one breaker or fuse circuit to another. (I’m only kidding about this stuff—I hope!)
In American residential homes, the individual 117-V circuits are usually rated for a maximum current of 15 or 20 amperes (or “amps,” abbreviated A). Once in awhile you’ll see a circuit rated at 30 A. The 234-V circuit (or circuits), if any exist, are rated at 20 to 50 A. When you use a lot of heavy appliances, you must keep these limitations in mind.
Table 3-1 lists several common types of household electrical appliances along with the amounts of current that they draw in a 117-V circuit. As a general rule, you should try to avoid going over the 2/3 point with any individual circuit in your house (unless you want to use a large appliance, such as an electric space heater or electric frying pan, of course). That means, for example, that you should avoid trying to load down a 15-A circuit with more than about 10 A, or a 20-A circuit with more than about 13 A. Once in awhile you’ll have to exceed this limitation, but you should stay within it as much as you can.
TABLE 3-1 Amounts of Current Drawn by Various Common Appliances in 117-V Residential Circuits
If your main electric distribution box has circuit breakers, the breakers will “automatically” force you to abide by their limitations. You’ll usually get a little bit of time, if you “max out” a particular circuit, before a breaker trips, unless you overload the circuit severely or subject it to a “dead short.” (Once, I made the mistake of using a diagonal cutter to sever a live electrical cord. The breaker tripped instantly. Fortunately, the cutter had insulated handles, and I was wearing gloves!) In the case of a fuse box, you’ll have less time. If and when a fuse blows out, you should always replace it with another fuse of the same type and the same current rating.
Warning! Never replace a blown fuse with anything other than the same type, having the same current rating. If you try to “cheat” by replacing, say, a 15-A fuse with a 20-A fuse, you’ll risk overheating the wires in your home, a notorious cause of electrical fires. If you replace a fuse with one having a smaller current rating, say a 15-A fuse instead of a 20-A fuse, you’ll be perfectly safe, although you might find the stricter limitation inconvenient.
Extension cords come in a great variety of lengths, with different wire sizes (or gauges) depending on how much current they can safely carry before they get too hot and pose a fire hazard. Figure 3-8 shows two common extension cords. The one on top measures 40 feet (approximately 13 meters) long and has three wires, while the one on the bottom is 6 feet (about 2 meters) long and has two wires. The shorter cord has a three-outlet block on the end, allowing for the connection of multiple appliances. Both cords are rated for a maximum load of 15 A at 117 V.
FIGURE 3-8 A 40-foot, three-wire extension cord for indoor/outdoor use, and a 6-foot, two-wire extension cord with three outlets for indoor use. Both cords are rated at 15 A.
Figure 3-9 shows a block tap that you can plug into a dual-outlet wall receptacle in order to use more than two appliances with that outlet. In this example, only two appliances are connected to the entire circuit, so technically the block tap isn’t needed. You should avoid using block taps in conjunction with high-current appliances, such as electric heaters, frying pans, or roaster ovens.
FIGURE 3-9 Proper use of a block tap in a 117-V electrical outlet.
Figure 3-10 shows a block tap used incorrectly with an extension cord. The three-outlet tap goes into one of the outlets in the extension cord that you saw in Fig. 3-8. This “tap-on-a-tap” scheme has an extra connection where the prongs of a plug contact the slots of an outlet. Every time you create a temporary connection like that, you run the risk of overheating, particularly with appliances that draw a lot of current.
FIGURE 3-10 Improper use of a block tap. Never cascade load-splitting devices one after another like this!
Warning! Never connect multiple load-splitting devices right next to each other in cascade (one after the other). If you fill up all of the available outlets in a contraption such as the one shown in Fig. 3-10, you’ll run the risk of overheating the splitters because they’re too close together. That will create a potential fire hazard, even if you don’t strain the circuit’s breaker or fuse. Also, if you use a high-current appliance in this arrangement (even a single one), you’ll create a fire hazard.
Most of us have computer workstations, and some of us have lots of peripherals and ancillary equipment, such as a printer, a scanner, a modem, a router, a cordless phone, a desk lamp or two, a charging bay (for devices such as tablet computers and cell phones), and so on. All of these things get their power, either directly or indirectly, from the 117-V utility system. As a result, anyone with a substantial computer workstation will end up with a mess of wires behind and underneath the work desk: a “tanglewire garden”!
“Tanglewire gardens” can look dangerous, as if they would inevitably present a high fire risk, but they don’t have to pose a hazard. If you know how to connect and arrange the wires properly, it doesn’t matter from a safety standpoint how much you tangle them up, although you might want to affix labels on the cords near their end connectors (on each end) so that you don’t get them confused with each other when the inevitable malfunction occurs and you have to pull out and replace one of the components of your system.
Figure 3-11 shows the “tanglewire garden” underneath my home electronics workbench. In addition to a computer, this system includes an amateur (“ham”) radio transceiver, two displays, an interface between the radio and the computer, a microcomputer-controlled power-measuring meter, an audio amplifier for the computer and radio, a wireless headset, a desk lamp, and an external hard drive that needs its own “power brick.” That’s 10 devices or cords in total, all deriving their power from a single outlet in the wall underneath the table!
FIGURE 3-11 “Tanglewire garden” beneath the author’s electronics workbench. A heavy-duty UPS (out of the picture to the right) serves two power strips mounted on a metal baking sheet that rests on detached plastic shelves.
In order to ensure smooth operation of the system in case of a power failure, all of the devices are connected to the wall outlet through a commercially manufactured uninterruptible power supply (UPS). The UPS has a battery that charges from the AC utility under normal conditions, but provides a few minutes of emergency AC (with the help of some sophisticated electronic circuits) if the utility power fails. That few minutes gives me time to deploy my backup generator without having to shut any of the devices down. The UPS has four outlets in the back, two of which go to power strips with six outlets each, and the other two of which remain empty. There are 12 available outlets in the power strips, 10 of which are engaged, as shown in Fig. 3-11. The UPS also has a transient voltage suppressor built-in. Figure 3-12 is a block diagram of the general arrangement.
FIGURE 3-12 Block diagram of the “tanglewire garden” beneath the author’s workbench. The power strips include breakers but not transient suppressors; the UPS contains a transient suppressor that serves the whole system. Gray arrows represent unused outlets.
I’ve taken three extra precautions, aside from making sure that I don’t overload the wall outlet, to ensure that my “tanglewire garden” remains safe. You should do the same with your pride and joy!
1. First, if you look carefully at Fig. 3-11, you’ll notice that I’ve mounted the power strips on a metal sheet. It’s a solid aluminum baking sheet. I glued the strips down there with epoxy resin. This precaution keeps the power strips from setting anything (other than themselves) on fire if they start sparking, a stunt that these things have been known to perform, occasionally with disastrous results.
2. Second, I have not allowed any cord splices or other sensitive electrical points to lie directly on the floor. The baking sheets, as well as all points in the cords where splices exist, are set up on thick plastic shelves. My basement floor will get wet if a huge, sudden rainstorm occurs. (Of course, in that event I won’t use the workstation until the floor dries out!)
3. Third, I’ve connected a dedicated ground wire from the chassis of the UPS to a known electrical ground. I tested the wall outlet underneath the workbench to ensure that the “third prong” actually goes to the electrical ground for the entire house. You can test the “third prong” of any three-wire outlet by following the procedure I describe in “Grounded, or Not?” a little later in this chapter.
You can use a long extension cord, along with your multimeter, to find out whether two 117-V circuits are on the same phase or not. If they’re on the same phase, the AC voltage between the two live outlet slots (shorter ones) will equal 0. If they’re on opposite phases, you’ll see 234 V, plus or minus a few percentage points, between them. Perform these steps in order, using Fig. 3-13 as a reference, and watch the results.
FIGURE 3-13 Arrangement for determining whether the phases of two 117-V utility circuits coincide or oppose. Make sure to set the multimeter to measure AC volts, with a full-scale rating of at least 250 V. Wear your gloves at all times.
1. Put on your rubber gloves and shoes.
2. Consider this test only for three-wire outlets, never for two-wire outlets.
3. Decide which pair of outlets you want to compare.
4. Plug a long three-wire extension cord into one of the outlets.
5. Position the outlet end of the extension cord next to the other outlet.
6. Set your multimeter for AC volts, with an upper range limit of 250 V or more.
7. Place the black probe tip of the meter into the shorter of the two rectangular slots in the extension cord outlet.
8. Place the red probe tip into the shorter of the two rectangular slots in the wall outlet.
9. Read the meter.
10. If the meter says 0 V, then the AC waves of the two outlets coincide in phase (in other words, they follow along with each other, as shown in Fig. 3-14A).
11. If the meter says 234 V (or something near it), then the AC waves of the two outlets oppose in phase (in other words, they buck each other, as shown in Fig. 3-14B).
FIGURE 3-14 At A, the electrical waves follow along with each other, so the two outlets have no voltage difference relative to each other. At B, the electrical waves oppose each other, so the two outlets have a difference of 234 V AC.
Many people assume that a three-wire 117-V utility outlet has a good ground at its “third hole” (the bottom hole, not either of the vertical slots). That’s not always true! I’ve seen cases where that “third hole” wasn’t connected to anything at all. You can use a long extension cord and your multimeter to find out whether or not a particular three-wire 117-V outlet has a good electrical ground at its “third hole.” Go through the following steps using Fig. 3-15 as a reference. For this test to work, you’ll need to find a reference outlet in your house that you know has a good ground at its “third hole.”
FIGURE 3-15 Arrangement for determining whether the “third prong” of an outlet is properly grounded. Follow the procedure for a continuity test. Always check for voltage before measuring resistance! Wear your gloves at all times.
1. Put on your rubber gloves and shoes.
2. Consider this test only for three-wire outlets, never for two-wire outlets.
3. Plug a long three-wire extension cord into an outlet with a known good electrical ground at the “third hole.”
4. Position the outlet end of the extension cord next to the outlet whose “third hole” you want to test.
5. Set your multimeter to measure the highest AC voltage that it can deal with.
6. Insert the multimeter’s black probe tip into the “third hole” in the extension cord outlet.
7. Insert the multimeter’s red probe tip into the “third hole” of the outlet you want to test, while leaving the black probe tip in the extension cord outlet.
8. Check the meter reading. If it shows anything other than 0, then an AC voltage exists between the two points, so your outlet does not have a good ground. It will present a shock or fire hazard if you use it.
9. If you see 0 as the result for step 8, switch the meter to the next lower AC voltage function and repeat the test.
10. If you get 0 again, repeat steps 8 and 9 with all the AC voltage functions that the meter has, going down until you’ve tested at the lowest AC voltage setting. You should always get a reading of 0. If you don’t, then you know that some AC voltage exists between the two points, so your outlet does not have a good ground.
11. Assuming that you’ve seen readings of 0 for all the AC voltage settings, repeat the tests with your multimeter’s DC voltage settings, starting with the highest one and working your way down to the lowest one. Test for DC voltage in both directions: first with the black probe tip in the “third hole” of the cord outlet and the red probe tip in the “third hole” of the outlet under test, and then the other way around. You should always see a meter reading of 0.
12. If you ever see any DC voltage besides 0 between the two points, then you know that your outlet does not have a good ground.
13. If you see 0 for all of the AC and DC voltage results, switch your multimeter to the highest resistance function.
14. Touch the meter’s two test probe tips to each other. If you’re using an analog meter, tweak the “0Ω ADJ.” knob so that the meter indicates 0. If you’re using a digital meter, make sure that the display indicates a value of 0.
15. Insert the black probe tip back into the extension cord’s “third hole,” and the red probe tip back into the outlet’s “third hole.” You should get a reading of 0.
16. Reverse the test leads. You should again get a reading of 0.
17. Repeat steps 14 through 16 for all the rest of the meter’s resistance settings, working your way down one setting at a time, until you get to the lowest one.
18. If you have observed readings of 0 for every step in the foregoing process, then you can have confidence that your outlet’s “third hole” is properly grounded.
19. If you ever see any meter reading other than 0 for the condition between the two “third holes,” you know that your outlet does not have a good ground. In that case, treat it as a two-wire outlet until you can get a professional electrician to wire it up properly.
If you live in the United States, you’ve grown accustomed to well-regulated AC that ranges from about 110 to 130 V RMS at 60 Hz. (The nominal figure of 117 V is commonly used for all such utility power.) Heavy-duty appliances, such as washing machines, electric ranges, water heaters, and central air conditioners, often use twice that voltage, ranging from about 220 to 260 V (and which we, in this book, refer to as 234 V), also at 60 Hz. However, in many other countries, the electrical specifications differ from those in the United States. The most common voltage is 234 V (give or take a few percent), often at 50 Hz rather than 60 Hz.
When it comes to AC, the frequency rarely matters in everyday use. In most situations, 50 Hz will do the same job as 60 Hz will. The exception is an old-fashioned electric clock that keeps its time based on a 60-Hz line frequency. (It will run slow at 50 Hz.) However, you can’t expect to plug a device designed for 117 V into a plug that delivers 234 V and get anything other than a catastrophe. Fortunately, the outlets in other countries usually differ geometrically from those in the United States, so you can’t simply plug your electric razor into a wall outlet in, say, Russia. You’ll have to buy an outlet adapter. Most good hardware stores stock outlet adapters. Radio Shack stores carry a good supply as well.
Before you travel to any other country (whether you live in the United States or not), check with a travel agent, and also with the authorities in that country, to make sure that you know what voltage to expect at the utility outlets. Also, make sure that you know what sort of outlet configuration you’ll find. The best travel agents will be able to tell you exactly which type of adapter and voltage converter you’ll need.
You can use the Table of Electricity at Utility Outlets in Various Countries throughout the World in the Appendix as a starting point to figure out what you should expect, but don’t take this table as a final authority. As mentioned above, double-check with government authorities in the country of interest, and/or with a qualified travel agent, before purchasing your adapters. At the time of this writing, a comprehensive information guide for voltages and adapter plugs throughout the world was available at the website http://www.voltageconverters.com/voltageguide.htm.
Warning! In some countries or remote locations, the voltage can fluctuate considerably from day to day, hour to hour, and even minute to minute. A simple voltage transformer or outlet adapter can’t do anything about such fluctuations.