Tripping breaker

[lisco]

We have a customer that has had some strange occurances in his home. Basically, it goes like this: He has an 1100 sq ft house that is 40 yrs old. He has lived there for 30 years. He replaced his subpanel two years ago. The panel looks proper. The senario is: he goes into the kitchen to turn on overhead flourescent light (relatively new). One out of 40 or 50 times he turns on the light it trips the breaker. He then leaves the switch in the on position. Turns the breaker back on, the light still does not come on; however, the breaker does not trip again. He then goes to his 240V window unit A/C, turns that on and the light comes on. I have traced the A/C wiring directly from the panel to the unit. There are no terminations or junctions with any other wire. It is a clean homerun. We have checked voltage, ampacity at the main panel, sub panel, branch circuits and feeder. Everything is as it should be. We have checked all of the lugs. We had the utility company check their transformers. We have checked every junction box, switch box and receptacle for loose connections, etc. We replaced the switch. We put AFCI breakers on all branch circuits.

Any ideas?

 

[480sparky]

I suspect they're tripping due to an arc fault and not being overloaded. Replace the AFCI breakers with standard breakers to see if they still trip. If they do not trip, then you know what to look for. Once you locate the problem, reinstall the AFCIs.

 

[charlie b]

It sounds to me that you put in the AFCI breakers as part of your troubleshooting effort, and that they were not a player in the customer's original symptoms. Is that right?

Next question: Did you personally observe any of the sequence of symptoms reported by the customer? Did you come into the house with everything working normally, starting turning that light on and off until it trips the breaker, leave the switch on and turn on the breaker, observe the light not turning on, then turn on the A/C unit and watch the light come on then? If not, then I would try to duplicate that sequence, and see if the system functions exactly as the customer has described.

I would try manually turning off the breaker that serves the light, and observe what else has lost power. There may be some other equipment that is a player in the sequence of operations. In addition, this may be part of a MWBC without anyone knowing it (no handle ties), and a loose neutral might be the cause.

 

[S'mise]

Lame Light Fixture

Lame Light Fixture

I would look at the light fixture. Maybe an old fashioned starter type that is not working right? Bad ballast causing the AFI to trip? I have seen loose bulb sockets give intermitant problems too. When he starts the AC unit, it's the dip in voltage at the light fixture helps the lamp to start.

 

[iaov]

I'ld start with the fixture and ballast/starter also.