The circuit breaker is an electrical device that opens an electrical circuit and stops the flow of current. In this chapter I am going to explain three types of circuit breakers that are used in our industry. Before getting into the text, let me inform you that circuit breaker manufacturers like to retain their individuality, making inter-changeability of circuit breakers impossible. Whenever you have the need to replace a circuit breaker or a neighboring component part of the circuit breaker panel, take all of the information you can get from the panel. Manufacturers name, model, serial number, style (if any), and sometimes the dealer will ask for the color. The three types of breakers I want to explain are, the non-trip, quick-trip, and slo-trip.
In many parts of the country, electrical code provisions have been introduced to help prevent accidents. The requirement for a service disconnect within sight of any piece of electrical machinery is the best known of these provisions. With this type of protection, accidental electrocution and other mishaps can be avoided. This service disconnect code has been complied with in several ways. A simple lighting switch has been used on residential units. The double-pole, single-throw switch worked without any problems. A pull-type disconnect has been used. This is composed of a pull block that has copper bus bars to make the circuit complete. When the block is pulled from the unit, the electrical circuit is opened. In Fig. 7-1 the typical pull-type disconnect is shown. A lever-type disconnect is also used. This type has bus blades mounted to a shaft. When the lever is pulled, the bus blades are pulled from the line lugs (receptacle where bus blades fit in to mate with the line side). Figure 7-2 shows this type of disconnect.
Fig. 7-1. Pull-type disconnect.
Fig. 7-2. Lever-type disconnect.
The non-trip service disconnect is an inexpensive and durable assembly. In Fig. 7-3 the disconnect can be seen as being very similar to an ordinary circuit breaker. Look very closely on the breaker assembly itself and the words “Non-Trip” will be stamped on it. There is an amperage rating for the unit also, perhaps this is where the confusion begins. The amperage rating applies to the amount of current the contacts in the switch will carry. Remember the amperage ratings that are used in relays and contactors; the same rule applies here. The higher the ampacity of this assembly, the more expensive it will be due to the contacts being constructed heavier to withstand the higher amperage loads crossing them. In many residential applications the 60-amp, non-trip breaker disconnect is used. The main thing to remember is that this breaker will not trip if overloaded.
Fig. 7-3. Non-trip disconnect.
This type of circuit breaker is manufactured for light amperage loads such as household lighting circuits. They can be obtained in 120 and 240 volt ac ratings. Their ampacity range is very wide. This type of circuit breaker was designed to trip (open the circuit and stop the flow of current) when the rated ampacity is exceeded. One of the advantages of the circuit breaker is that you do not have to find a hardware store open in the middle of the night when a circuit breaker trips. The resetting device eliminates the need of having a box full of fuses that always seem to be the sizes you don’t need.
This type of circuit breaker has been designed to conduct the locked rotor loads of starting motors and other initially high, resistive loads. These breakers are usually double breakers for 240 volts single-phase and triple breakers for three-phase equipment. Both types have a link that ties the circuits together mechanically. For instance in a three-phase compressor, the current in conductor L3 becomes excessive. The L3 switch begins to open, and as it moves, the mechanical link opens L1 and L2, thus eliminating the possibility of single-phasing.
Some equipment manufacturers use a circuit breaker such as these in their equipment as a service disconnect and to afford extra protection for the equipment. This will be found mostly on light commercial and heavy commercial equipment. The logic is that the compressor manufacturer will save money on warranty claims. In the installation the circuit breaker installed by the electrician might be too large, or more than one unit might be on the main breaker. This safety in the unit itself has proved to be a cost-saving device for many manufacturers.
With a voltmeter, place one test probe on one of the screw lugs (screw that locks conductor into the circuit breaker) and the other test probe on the neutral bus bar. In the case of a 120-volt ac circuit breaker, 120 volts should be read on the meter. In the case of a 240-volt ac breaker, one probe should be placed on each screw lug of the breaker. The voltage should read 240 volts ac on the meter. If you test with one probe on the screw lug and the other on the neutral bus bar, each should read 115 volts ac.
This test is done only by overloading the circuit. With a snap-on type ammeter placed over the conductor of a circuit the amperage can be read. In a lighting circuit, the breaker rating is usually 15 amps. By placing an increasing load on a circuit such as lighting, lamps, toaster, or any other electrical device, you can slowly raise the amperage load on that conductor while observing the increasing current. If the circuit breaker is rated for 15 amps and trips when the load reaches 11 amps, the breaker should be replaced.
To check an electric motor circuit, the same principle applies. With a machine there is a slight risk of damage. If a unit is old and on its last leg, you might put the finishing touches to it by performing this test. When a compressor trips the breaker and there is a doubt whether the circuit breaker is defective or not, perform the following test. With the ammeter applied to the conductor that supplies the compressor, turn the compressor on and observe the amperage. It will probably be operating within the limitations of the circuit breaker. In order to cause the amperage to raise, cover the condenser fan inlet or outlet. This will cause the compressor to operate at higher compression pressures, thus causing a higher current to flow through the circuit breaker. Observe your ammeter to make sure the amperage doesn’t exceed the FLA of the compressor.
With the circuit breaker removed from the panel, a continuity test can be made to see if the switch resets and to measure the amount of resistance across the contacts. Figure 7-4 shows a typical circuit breaker entrance panel. The one in the picture has screws around the perimeter of the cover. Some have screws inside the cover that removes a cover plate. Removing these screws very carefully and removing the cover without touching any of the wiring will expose the conductors to the different circuits in the house. Notice there is a main circuit breaker; all of the breakers can be turned off including the main, this will decrease the chances of you grounding a circuit. Remember that there is still voltage in the panel. The only way to eliminate all the electricity from the panel is to remove the power company meter. This can only be done by an electrician or the power company. In Fig. 7-5 the two conductors from the electric meter feed the main circuit breaker. Figure 7-6 shows the two line bus bars that the circuit breaker engages with, to pick up current and transport it through the branch circuit conductor. Figure 7-7 shows the neutral bus bar which is the return conductor of the 115 volt ac circuit. The breaker can be removed by disconnecting the conductor from its screw lug, then pulling up on the side that is in the center of the panel. The breaker plugs into the bus bar rail. Lift it out of the panel and now you can either test it or replace it. Figure 7-8 shows a typical circuit breaker.
Fig. 7-4. Circuit breaker panel.
Fig. 7-5. Circuit breaker panel with cover removed. Two main feeder conductors are indicated.
Fig. 7-6. Breakers removed to show the two bus bars providing 120 volts each thus giving 240-volt service in the structure.
Fig. 7-7. Neutral bus bar used for one leg of all 120-volt circuits in the structure.
Fig. 7-8. Typical linked circuit breaker, with double thickness which straddles both bus bars, protecting 240-volt supply.
In many locations, it is not a bad idea to check a circuit breaker panel from time to time to see if the wiring to the circuit breaker lugs is tight. In some cases, wires can work loose from vibrations and expansion; in the case of aluminum wiring this condition is especially true. Claims have been made that there is a distinct possibility that loose wiring in the entrance circuit breaker panel might cause an arcing that results in fire. On a service call, if the circumstances warrant it, it is a good idea to check the wire connections to each of the circuit breakers in the customer’s panel. You and the customer will sleep better knowing that you checked a possible fire potential.
