Question about troubleshooting an AFCI-protected circuit
In the spirit of full disclosure, I'm an apprentice doing this work for a family member. If this violates policy, please delete this.
Last night I was troubleshooting an AFCI circuit. HO reported that the breaker trips at random, that it went for about a year and a half without tripping, and then started again. Said he couldn't find a consistent pattern for when it trips.
The breaker was in a subpanel. Three homeruns were spliced together and pigtailed onto the breaker. After checking all the basics (screws on breaker/bus bar tight, etc), I found that the neutral pigtail was broken about 80% of the way through the wire and about to come off. Fixed it. Circuit still tripped in what appeared to be a random way.
Started the process of elimination by putting the homeruns on the breaker one at a time. Chased it down to a bathroom light/fan fixture. The tab that connects to the bottom of the bulb had a burn mark on it, as did the bottom of the bulb. I tried putting it on a different AFCI, and also on a regular breaker. It still tripped.
Disconnected the light portion of the fixture and put everything back on the original AFCI breaker, and it would not trip. HO says he wants to replace the socket in the fixture (I didn't have the part with me). I could not get the thing to trip without the light portion of the fixture in the circuit.
Would the fact that the three homeruns were spliced together cause the breaker to trip when something other than that light is activated? Also, why would it go without tripping for 1.5 years, and then restart again?
Thanks in advance.