2

We remodeled our home and had all new electrical put it in to plan.

For rough-in, the electrician put in regular breakers instead of arc fault breakers. Arc fault breakers are required by code now in Houston, TX, so near the end of the project, the electrician removed the regulars and put in AF breakers.

(Note: GFCI breakers were of course also used, but they're not part of this question.)

Several AF breakers tripped immediately. The electrician fixed the issues on most of them, but the final two he just took the AFs out and put regular breakers back in. Our General Contractor gave the OK, and the city inspector passed it. But I don't buy that this is non-issue and plan to fix it myself.

(Full disclosure: I'm an electrical engineer and have done home wiring before, but I am not a licensed electrician and have no experience with arc fault breakers and how they work.)

Question:

What's the typical workflow to troubleshoot a tripping arc fault breaker for a newly wired home?

  • Did they offer any explanation as to how they "fixed" the other circuits, or how they avoided using them on these circuits? I'm assuming the Electrician gave the inspector a good enough reason as to why he didn't use the AFCI breakers. – Tester101 Feb 7 '15 at 18:07
  • @Tester101 As I understood it, they said the neutrals for the two circuits with regular breakers were connected together somewhere down the line. – CivFan Feb 7 '15 at 18:56
0

This behavior is because arc-fault breakers have an interesting quirk: they also provide a small degree of ground fault protection as well! (They are not GFCI's because their ground-fault trip threshold is set to the 30mA used for equipment protection (GFPE) devices as opposed to the 5mA ground-fault (differential) trip of a Class A personnel protection GFCI.)

You will need to contact your electrician and tell them to get their neutrals straight. Tell him he violated NEC sections 200.4:

Multiple Circuits. Where more than one neutral conductor associated with different circuits is in an enclosure, grounded circuit conductors of each circuit shall be identified or grouped to correspond with the ungrounded circuit conductor(s) by wire markers, cable ties, or similar means in at least one location within the enclosure.

300.3(B):

Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).

and 310.10(H)(1):

General. Aluminum, copper-clad aluminum, or copper conductors, for each phase, polarity, neutral, or grounded circuit shall be permitted to be connected in parallel (electrically joined at both ends) only in sizes 1/0 AWG and larger where installed in accordance with 310.10(H)(2) through (H)(6).

  • Great source references. Do you have a plain English summary of each? – CivFan Feb 24 '15 at 17:13
  • It boils down to the fact that current flows in loops: what comes out on a circuit's hot is supposed to come back on that circuit's neutral, and only that circuit's neutral. Otherwise, you have large loops that emit 60Hz fields -- these can cause induction heating of ferrous metals and interference with sensitive equipment. GFCIs, of course, also don't like this situation, and trip when presented with it -- in fact, the test button on a GFCI doesn't need a ground to work as it simply connects load-hot to line-neutral via a current-limiting resistor. – ThreePhaseEel Feb 24 '15 at 23:11
  • Full disclosure: we had to get a second electrician to take over the last 10% of the electrical renovation. Unfortunately since the first electrician created this problem, it won't do much good to go back to him and tell him, again, he screwed up and needs to fix it. The second electrician who saved us in a pinch, would be happy to fix it under another contract, but the budget is not there any longer. Accepting the answer as the references you sourced and described seem ironclad. – CivFan Mar 20 '15 at 21:16
  • "in fact, the test button on a GFCI doesn't need a ground to work as it simply connects load-hot to line-neutral via a current-limiting resistor." -- wait, why does that trip the GFCI? Wouldn't that still return on the correct circuit's neutral? Oh... I guess it's because it doesn't go through the GFCI's sensor path? – CivFan Feb 24 at 3:19
  • @CivFan -- exactly! It bypasses the GFCI's sensor path directly instead of relying on the ground wire to do that. – ThreePhaseEel Feb 24 at 3:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.