Why you trippin'?
By Jimmie Slemp, WECA Instructor and Lab Manager
Recently, I was called by a WECA alumnus and asked if I could help with a problem. It turns out the electrician had done a pretty extensive remodel and repair job on a house that had previously been in a fire. All the rough and trim work was completed and he was making the final connections in the panel. He told me that two of the circuits were tripping the AFCI breakers and that when he connected the circuits to a standard circuit breaker--the circuits worked fine. Huh?
The house was close and I said I would drop by on my way home from WECA. On the drive over I started thinking of what could be wrong? I had a good idea of what was going on, but of course I would have to check it out to be sure. Based on the symptoms, what do you think is going on?
Upon arrival I found that the electrician had the two circuits in question disconnected from the circuit breakers and the neutral busbar. I got out my meter and decided to do a few continuity tests.
Here is what I found - Hot to Neutral = No, Hot to Ground = No, Neutral to Ground = Yes. Do you know what the problem is?
The continuity between the neutral to ground is the issue. Somewhere in the branch circuit these two conductors are making contact. A normal circuit breaker cannot detect this contact but an AFCI breaker monitors the neutral conductor. AFCI breakers typically have a limited amount of ground fault protection - not to be confused with the class A GFCI which trip at 4-6 milliamps, but at a slightly higher level of 30-50 milliamps.
So we proceeded to look for the actual problem. We started roughly in the middle of the circuit and removed the neutral conductor from the receptacle and retesting to determine which part of the circuit had the fault until we eventually found the problem. It turned out that while pushing the receptacle back into the box, the grounding conductor had made contact with the neutral screw terminal, causing the AFCI breakers to trip.
To keep from tripping breakers, especially with a grounding conductor being bare in the NM Cable, a little care should be used to push a conductor back into the box away from the receptacle. Problem solved. Now who's trippin'?