ECN Forum Forums Code Related Discussion NEC & other Code issues brain teaser

I have a AFI that keeps tripping when I turn the lights on, when I take all the bulbs out the circuit holds...ok bad AFI right? Wrong, for kicks and giggles I removed the neutral from the AFI and landed in the busbar and tested the lights again, and again they tripped the breaker. Anybody seen this b-4? It seems if the switch leg was crissed cross to the neut, then the circuit would trip regardless if the lamp was present. What are some other reasons you guys can think of?

Neutrals from two circuits tied together or a neutral faulted to ground. Arc fault breakers also trip on a ground fault.

I agree with you twh. But I took the neut out of series with the AFI(standard breaker now. I should be more specific that with the light bulbs out, I can turn switch on and read 120V on the switch leg side of the switch. Put in lamp and turn same switch and breaker trips.

Have you tried a different lamp in the fitting, the filament may be about to break.

Shared Neutral downstream? AFCIs do not like shared neutrals, anywhere in the circuit. The fact that the AFCI trips when the lights go on, but not before, may further indicate the shared neutral possibility. Directly landing the neutral in the panel would have no affect on this issue. The neutral would still be shared within the branch circuit(s).

Good Luck!

I’ve seen that exact same thing happen twice before. Both were because of damaged NM cables in the walls on new construction. The neutral and grounding conductor where mashed together in the wall. Luckily these were not on my own jobs, but I still had the unfortunate task of locating the problems for someone else.

Sometimes the grounding conductor and neutral are touching somewhere downstream in one of the receptacle outlets. It could cause AFCI tripping when a load is applied, meaning something is plugged in or a light on the circuit is turned on.

Removing the neutral from the AFI and landing it directly to the bus bar will trip out the unit on ground fault if any current at all passes through the hot conductor, just like if you'd done it to a GFCI. This method can't be used to troubleshoot.

If the AFCI only trips when the light switch is turned on, even if there are no bulbs in it, I suspect a wiring fault with the hot conductor, either a crossed neutral connection or a short circuit somewhere. Nail through NM will do this. At least you can narrow it down to that lighting string!

Either way, it's been a month, did you ever find the cause?