AFCI Circuit Breaker Troubleshooting

An arc-fault circuit interrupter (AFCI) is a circuit breaker located in your electrical panel that serves the functions of a normal breaker but also senses hazardous arcing on its circuit and will trip off for this. It can be identified by the special colored test-button near its handle. (Ground-fault breakers also have a button, so read with a magnifying glass to be sure which kind your breaker is.)

AFCI breakers began to be required by Code in 2002 for new wiring supplying bedrooms. The areas to be protected were expanded in 2008 (where that national Code has been adopted locally) to most rooms of the home. The areas left out of the requirement were garage, bathroom, kitchen, and laundry; these were already required to have ground-fault protection. Apparently two-fold protection is considered overkill.

It is relevant to AFCI circuit breaker troubleshooting to note that overkill was, however, required of manufacturers from the beginning: the arc-fault circuit interrupter must have a degree of ground-fault protection built into it as well. The rationale seems to have been that as long as a new device (the AFCI) was being designed, it should incorporate super-safety by tripping off for ground-faults too. At first, the level of ground-faulting was not required to be as strict as GFCI outlets around the home have. But by now, I understand that many AFCI brands have the same sensitivity as the GFCI outlets. It would make sense that the Code should simplify itself (and life) by just requiring all 120-volt wiring in the home to have protection from AFCI circuit breakers which incorporate the more sensitive ground-fault protection. Then all these GFCI outlets around the home could be eliminated.

These facts present a problem for AFCI circuit breaker troubleshooting. When these breakers in newer homes trip off, there are five possible causes:

An Overload -- when electrical usage would have begun to overheat a circuit's wires
A Short Circuit -- very high current resulting from a fault on the circuit
An Overheating Breaker -- when the breaker itself has poor contacts or connections
A Ground-Fault -- leakage off of the intended circuit. In this I include shock hazards, neutral to ground faults, and the "fault" that occurs to the phase of another circuit if these two circuits share one neutral.
An Arc-Fault -- sparking happening on the circuit or its lights or appliances

A standard breaker will trip for any of the first three causes above, and it can take some thought and investigation to determine which cause is at work. But the fourth and fifth causes add even more complication. Which of the five causes has tripped an AFCI breaker can be quite important in how you go about solving the problem.

In the case of an arc-fault breaker that is introduced into an existing home, a common cause of tripping will be that the neutral of the circuit is mixed somewhere with the neutral of another circuit. The tripping may be immediate or may only happen when something on either circuit is running. The two common places this mixing of neutrals would occur are at a 2-gang or 3-gang switch box where both circuits are present, or in a 3-way switch system where the neutral for the light(s) has been borrowed (improperly) from the other circuit. To ferret out this sort of thing, many people will find they need a Local electrician to come.

If the AFCI breaker lets you reset it and does not repeat its tripping, you do not need to know or to worry about the cause. For the record, it was probably an overload or an arc-fault that was only a one-time event.

If the arc-fault breaker re-trips immediately (up to 5 seconds) when you reset it (see How to be sure you have reset), this is typical of a short circuit or a ground-fault. If re-tripping only occurs from one minute to one month later, the cause is more likely an overload, an overheating breaker, or an arc-fault.

For systematic help to troubleshoot these various causes, see Troubleshooting or Diagnosing. In order to tell specifically whether it is an arc-fault that is causing repeated tripping, you might have to temporarily replace the AFCI breaker with a standard breaker (putting the solid white wire from the AFCI's terminal into the panel's neutral/ground bar). If the standard breaker holds, then the problem is either an arc-fault or a ground-fault. If so, you could then introduce A GFCI receptacle (with a white piece from the neutral bar to "line" neutral on the receptacle) after the standard breaker. If the GFCI holds, the problem was an arc-fault; otherwise, a ground-fault.

If you have a recurring arc-fault, rather than one of the other conditions that will trip an arc-fault breaker, what signs will you be looking for out on the circuit? Although you might find something melted, charred, or sooty, an arc is more likely to trip the breaker without leaving visible signs. In any case, if the tripping continues to repeat without much delay, the Procedures for diagnosing the location of a short should be applied.

Also, as long as you do not leave it in place beyond your time of vigilant searching, a standard breaker, as mentioned above, could be put in the panel in place of the AFCI. You might then be able to hear, see, or smell signs of heat or arcing; blinking lights on the circuit would give additional clues. I am comfortable suggesting what might sound like playing with fire, because few cases of arcing are ever able to start fires. In most homes (most don't have AFCIs), when arcing at connection points ("series" arcing) has been happening for a while, it does commonly show itself eventually as a partial outage of the circuit, from the arcing point on. This can then be troubleshot more easily. But a 2005-or-later AFCI may not let the problem get to the point of interrupting power in this way; if the series arcing is large enough, this AFCI would stop the arcing before it could start to affect things in this way.

What is the difference between series arcing and parallel arcing? Series arcing (a kind of partial open) would occur along the normal circuit path, typically at connections meant to pass the normal current of a load along. With parallel arcing, on the other hand (as with a short circuit), current runs from hot to neutral or to ground, unlimited by any loads of the circuit.

How common in practice are arc-faults? In all my troubleshooting, from when these protected circuits began to be required for bedrooms in 2002 up to the present, I have not once been called on to deal with a repeatedly tripping AFCI. This may change a little beginning in 2008, because more rooms of new homes must have the protection. So far, the arcing faults an AFCI will interrupt do not seem to me to be very common at all.

Many people will think that a tripping breaker has something wrong with it. This would be rare. One reason an AFCI would trip immediately is that its white neutral or that of the circuit is not hooked up right (this will be a case of tripping for a fault -- namely the fault of the installer). The most common way an AFCI is actually bad is when its Test button will not trip the breaker. With that, there isn't much AFCI circuit breaker troubleshooting to do; just replace it; there is something wrong with it.

Finally, a note on how Code on AFCIs will affect new wiring practices. Where the 2008 or later national Code is adopted, dining room receptacles are required to be AFCI protected. Since they are commonly put with some kitchen receptacles on one circuit, and since such kitchen outlets have a GFCI requirement, there may now be a circuit run from an AFCI breaker that will also have a GFCI outlet along it. With the AFCI already sensing a degree of ground-faulting, there might be a potential for nuisance tripping or at least confusion over where a ground-fault is occuring. An alternative is to add one more AFCI breaker to the panel to serve just dining room receptacles.