Help tracing a fault?

[ChuckTH]

Hi - just a DIY homeowner here... 1950's house, 20 amp lighting circuit, total of 10 bulbs and one kitchen exhaust fan on the circuit (all led or florescent bulbs). If I use a regular old 15A breaker everything seems to work fine. If I use a 20A GFCI/AFCI breaker one light fixture consistently trips it (with or without anything else on at the time.) I am not sure whether that fixture is first, last, or in between others on the circuit... What "assumptions" can I make about what is tripping the breaker? "ground fault"? "arc-fault"? - Can I assume that because no other combination of lights trips it, that the fault is either "within" the fixture itself? - or that the fixture is the last on the circuit and the fault is somewhere in that last run of the wire?... Thanks in advance for your patience with this novice! ?

 

[littlespark]

As American poster, I’ll tag @Megawatt here so he can advise.

To explain, it won’t matter where the fixture is in the circuit, as wherever there’s a switch, that’s a branch off the main circuit.
If this light only trips the breaker when it is turned “on”, then the fault must be from the switch to the light.
I don’t know how competent you are with electrics, but you could, with the power off, remove the switch and light and check for wires that have been damaged.
you could also look for moisture getting in anywhere.

I’m wondering if it could be a faulty switch?
Would that trip an arc fault device? If the switch wasn’t closing properly??

 

[DPG]

And does the combined breaker give an indication of whether an arc fault or a ground fault tripped it?

 

[Megawatt]

Hi - just a DIY homeowner here... 1950's house, 20 amp lighting circuit, total of 10 bulbs and one kitchen exhaust fan on the circuit (all led or florescent bulbs). If I use a regular old 15A breaker everything seems to work fine. If I use a 20A GFCI/AFCI breaker one light fixture consistently trips it (with or without anything else on at the time.) I am not sure whether that fixture is first, last, or in between others on the circuit... What "assumptions" can I make about what is tripping the breaker? "ground fault"? "arc-fault"? - Can I assume that because no other combination of lights trips it, that the fault is either "within" the fixture itself? - or that the fixture is the last on the circuit and the fault is somewhere in that last run of the wire?... Thanks in advance for your patience with this novice! ?

You have a very old house and you don’t know how many people have worked on your house. My advice would be to just leave the regular breaker in your panel. If someone is sharing neutrals which you wouldn’t know and the AFCI or GFCI breakers don’t like what there are seeing. The only way you can fix that is to either open up your outlets and lights plus fan and eliminate them one at a time using the GFCI not the AFCI. The reason is AFCI breakers often trip for no apparent reason