Decoding the Mystery of Your Electric Service Panel

Perhaps you’ve made the journey to your electric panel after the lights went out to see if a circuit breaker had tripped. As you stared into that panel (maybe even in the light of a flashlight), did you wonder what you were looking at? Those breakers serve very specific functions to protect you and your home from electricity.

Circuit Breakers

Circuit breakers began to be used in the United States in the 1960’s. Before that, fuses were the means of providing protection. But circuit breakers, simply put, protect a home’s electric circuits from an overload … or from too much electricity flowing through the branch wiring.

Such an overload is a risk because if a wire carries more electricity than it is designed to carry, it can melt and become both a fire and an electrocution hazard. So when that circuit breaker trips, it is simply telling you that something was trying to get more electricity than is safe for that circuit. This can occur when you try to use more devices than can be safely supplied at once (i.e., when you have the hair dryer and space heater on at the same time), or it can occur when there is a short circuit. A short circuit occurs when the hot wire comes into direct contact with either the neutral or the ground wire. A short circuit would enable more amps to flow than the wire could safely handle, therefore the breaker will trip in order to protect the circuit.


GFCI’s (Ground Fault Circuit Interrupters) protect against ground faults. These kinds of circuit interrupters began to be used in the 1970’s. They have the ability to recognize a fault to ground (also called a short to ground) extremely quickly.

A common way this kind of fault can occur in the home is when electricity is brought into contact with water. A person can inadvertently complete a path to ground between a hot wire and a water source in the home. However, a GFCI protected receptacle will recognize that less electricity is returning on the white, neutral wire … this is because some of it has begun to flow to ground via the person who completed the connection with the wet location. It quickly recognizes this as a ground fault and interrupts (or stops) the electrical connection even faster than a hazardous shock can occur.

Ground fault protection can be attained with either GFCI breakers or GFI (Ground fault interrupter) receptacles, and such protection is required in all wet locations (kitchen, bathroom, garage, crawl spaces, outside, etc.). Read this article for more information.


AFCI’s (Arc Fault Circuit Interrupters) began to be required in the United States in 1999. They recognize when there is an arc occurring somewhere in the system. An arc occurs when electricity flows across the air between two points. There are two kinds of arcs: parallel and series.

Parallel arcs occur between two different wires. For example, if a wire in a wall is nicked by a nail or screw, the exposed wires may begin to arc from the black, hot wire to either the neutral or the ground wire. A series arc is an arc that occurs along the same wire. For example, at bad connection points in receptacles or switches, an arc may jump across the air at that bad connection.

The problem with arcs is that they generate heat which in turn can cause a fire. AFCI’s recognize the patterns that arcs create, and they shut off power to that circuit before a fire can occur. Some AFCI’s only recognize parallel arcs, but now we have Combination AFCI’s that can recognize both parallel and series arcs. (Combination AFCI breakers should not be confused with Dual Function breakers which provide both AFCI and GFCI protection.)

AFCI’s can be installed as breakers in the main service panel or as receptacles. However, an AFCI receptacle will not detect arcing in the circuit upstream of itself (i.e. between the service panel and that receptacle). For this reason, most of the AFCI protection you will see are breakers in the main service panel so that the entire circuit is protected. The National Electric Code now requires AFCI protection for most areas of the home. For more information read this article.


Both GFCI and AFCI breakers should be tested monthly by pressing the test button. If the breaker trips, then you are good to go. GFI receptacles should also be tested monthly by pressing the test button. Be sure to reset all breakers and receptacles that you test. If the breaker or receptacle doesn’t trip when the test button is pressed, then it should be replaced.

In Summary

To summarize, circuit breakers protect your home’s wiring from electrical overloads. GFCI’s protect your home’s occupants from electrical shock. And AFCI’s protect your home from fire. GFCI and AFCI breakers should be tested monthly. I hope this demystifies some of what you see when you open your electrical panel door.

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