Arc Fault trips under load

[RLyons]

Trimming a house when I rang the doorbell the Arc fault tripped. I had already used one of those cheapo plug testers on the circuit and it checked out no reverses ect... I changed out all the doorbell parts only to find out the circuit tripped under load. I replaced the breaker with another arc same issue, replaced it with a GFI and it wouldn't even hold, standard breaker held. I traced it to an outside GFI fed directly from an inside outlet with no pass through. Remove outlet from equation and everything worked fine. Pulled out and checked connections taped around GFI put back in box and the breaker now holds. I know Arc's trip instantly when ground and neutral is touching or a direct short. So my question is what caused it? The circuit doesn't pass through the GFI which means the load doesn't so what would cause the arc fault to trip? It never customary for me or other people I know to test beyond the cheapo plug in tester. I have the amprobe INS-3 and feel I should start testing all circuits after installation.

 

[kwired]

Trimming a house when I rang the doorbell the Arc fault tripped. I had already used one of those cheapo plug testers on the circuit and it checked out no reverses ect... I changed out all the doorbell parts only to find out the circuit tripped under load. I replaced the breaker with another arc same issue, replaced it with a GFI and it wouldn't even hold, standard breaker held. I traced it to an outside GFI fed directly from an inside outlet with no pass through. Remove outlet from equation and everything worked fine. Pulled out and checked connections taped around GFI put back in box and the breaker now holds. I know Arc's trip instantly when ground and neutral is touching or a direct short. So my question is what caused it? The circuit doesn't pass through the GFI which means the load doesn't so what would cause the arc fault to trip? It never customary for me or other people I know to test beyond the cheapo plug in tester. I have the amprobe INS-3 and feel I should start testing all circuits after installation.

AFCI's don't necessarily trip instantly on a N-G fault, but will when a load is added. GFCI's will trip instantly on a N-G fault. They have special circuitry designed to make them trip instantly when this happens. You maybe had a N-G fault in the receptacle you took apart and you ended up clearing up that problem when you took it apart.