We recently upgraded the service on an older house. The City requires us to put arc fault protection on the bedrooms. We did on 2 out of 3, but 1 circuit wouldn't hold on the arc fault. The inspector won't pass the job until that circuit gets an arc fault breaker. I'm sure somewhere on the circuit someone at some time tied the neutrals from another circuit to it, but it could be something else.

Does anyone have a tip on how to find problem without rewiring the house?

If you have already done this I apologize.
1.Not fed on a multi wire circuit is it?
2.I would swap out with another arc fault breaker.
3.I would kill the circuit,see what is dead,go to the halfway point of the circuit and open it up ,seperate the wires,energize it see if it holds and reapeat and continue to narrow the possible location down.Sounds like there is a neutral problem or an actual arc problem.
4. older home is there lighting on the circuit?could they be switching a neutral for light control? (common in K&T wiring)
(don't know if that would cause the arc fault to trip though.)
[This message has been edited by andyp95 (edited 09-27-2004).]

[This message has been edited by andyp95 (edited 09-27-2004).]

Mostly agree with Andy, but if you have available try with a GFI breaker, that should speak to possible crossed nuetral problem. Have everything unplugged when testing as bad cord may be cause.If you've already done, sorry; sometimes obvious things escape us when trouble comes.LOL.

AFCI does have some ground fault protection, so you may be correct about the shared neutral.

Not sure about the best way, but turn everything off except the AFCI circuit, disconnect it's neutral and load the circuit. Not on the AFCI breaker, of course. Then use an ammeter to find the other neutral. Next, turn the other circuits on until you find the other hot using that neutral.

If it's K&T pull both circuits out of the panel and put them in one box and feed them with the AFCI circuit. Since K&T doesn't follow the rule about all conductors of a circuit in one cable, you should be able to abandon one neutral.

If it isn't K&T, the crossed neutrals will be in an accessable box, right? Then you could fix it the proper way.

Around here, we can change panels without taking responsibility for every plug in the house. You have my sympathy.

you could remove all the neutrals (excluding the one from the strange circuit) from the neutral bus, and ohm-meter which of the removed neutrals does still have connection to the N Bus. No idea if possible, but that's how we'd do it here.

otherwise open up and check all connections to the bedroom for a real arc fault possibility like loosened wirenut etc,

I would also question the inspector's authority to require arc-fault protection on existing circuits just because you changed the main panel. What you have done has increased the safety of the house, not decreased it. To require existing branch circuits to be upgraded to AFCI exceeds the intent of the code, which is for all NEW construction to meet the AFCI requirements.
Did this same inspector also require the receptacles in the kitchen to be upgraded to GFCI? Did you have to add a 20 amp GFCI receptacle in the bathrooms? Did you have to add smoke detectors throughout the house?
I'm sure this inspector has a boss, who would be willing to listen to your comments.
This kind of piling on the code leads to electricians not pulling permits, or homeowners hiring the part-timers who won't pull permits.

If the existing circuits are in a wiring method that does not include an equipment ground such as type NM/B you may have violated the manufactures instructions (110.3 (B))

I agree the NEC is not Retro in it,s requirements.

good luck

Charlie

Thanks for the advice, I'll pass it on to the crew that's going to the house and it might save me a trip to it.

Around here in every jurisdiction we work in they require Arc faults on the bedrooms, GFI's in the bathrooms and kitchen and hard wired smoke detectors to be added when we do a service change. This inspector is also requiring a GFI receptacle to be added in the powder room that never had any outlet before.

Your sympathies are appreciated.

A while back I had a arc fault nightmare too. Turned out to be a flat screen computer monitor, tripped the breaker everytime it went into sleep mode. Drove me nuts for a while. Hope you find your problem.

With the main disconnet open insure that the panel is dead (You could just open every brake in the panel but killing the main is safest.), lift the hot and neutral of the circuit in question. With everything in the house unplugged or off and all breakers open, connect a circuit tracer, (fox'n hound) to the neutral and it will track to any other neutral that is connected and you can see it in every box that it runs through. You have to go through every junction box affected and open the neutrals till you break the errant connection. (it will also seek anything that is still on the line) Good luck

I recently had a problem with a AFCI when adding outlets to an older home. Once installed everything worked on the old breaker but the new one would trip as soon as I applied any load. After opening every juction on the circuit, I discovered that an existing ceiling fixture had a short between GROUND and NEUTRAL. This caused the tripping. Fixed that and it worked fine.