AFCI 2 pole circuit breaker tripping?

[olc]

Existing apartment with two general receptacle/lighting circuits that included the bathroom. The circuits were wired as a 3 wire circuit (one neutral). The loadcenter was replaces and a 2 pole AFCI circuit breaker used for these circuits. Now it is tripping. Will a fan (bathroom ceiling exhaust fan) starting trip the AFCI circuit breaker? Use of the GFI receptacle in the bathroom? (Square D 2 pole AFCI homeline circuit breaker)
Thoughts?

 

[cowboyjwc]

Could be the fan, but could be a staple that was put in when the original install was done, or a nail. Could be numerous reasons that an AFCI that's newly installed on an old installation would trip. That's why we don't require them on service changes, since the wiring is not being modified or replaced or extended.

 

[mopowr steve]

Since the installation you describe is a MWBC it could also be possible it dates to a time when all neutrals from even other circuits could be tied together with the MWBC neutral therefore it would trip the AFCI.
Does it occur specifically to operating a switch, etc.?

 

[electricalist]

A gfci in the bathroom . I dont remember that a gfci will work with a shared neutral. disconnect one line of the mwbc, see if it resets if it does put it back and remove the other line and reset, if it trips the problem is in something not on if it resets its a wiring error.
Finding a problem is a matter of deduction.
unplug any thing thats pluged in . Turn off every light ,,appliance ,trip every gfci.
Now begin hunting arc fault wabbit...
if both lines are connected to afci breaker and it resets,,start with turning on one switch at a time hopefully its not them so you can see when you find the problem.
Most often i find a grounding conductor touching a grounded terminal,,,(ground touching neutral) in a plug and trips when theres a load on the neutral..example you turn the light in the bedroom on and it trips but the light arent the cause its in the plug on the same circuit...

 

[Dennis Alwon]

Since the installation you describe is a MWBC it could also be possible it dates to a time when all neutrals from even other circuits could be tied together with the MWBC neutral therefore it would trip the AFCI.
Does it occur specifically to operating a switch, etc.?

All neutrals are tied together with a multiwire branch circuit--how else can it be done but a DP afci should work fine with it. The thing is you have to isolate the problem. Disconnect one leg from the breaker and see what circuit the problem is on. Then go from there but remember an afci- if that is the cause of the trip- needs 4 or so amps before it will sense the fault. GE and perhaps Seimens are the only manufacturers that have taken the gfci out of the breakers. I am not sure about seimens but a member here says that is the case. When I called Seimens they said that was not so but that guy seemed to not understand the question very well so I wouldn't trust his response.

 

[electricalist]

What about square d homeline afci?

 

[ActionDave]

What about square d homeline afci?

Their AFCI breakers still have ground fault circuitry, 30ma I believe. SqD also has a
Dual Function AFCI/GFCI breaker.

I agree with Dennis, the only brand AFCI that I know for sure does not have a GF component is GE.

 

[electricalist]

The op said it was Homeline but I guess like Dennis said the neutral has nothing to do with it. I thought how a Gfci trips with a shared neutral but a 2 pole is designed to work that way.

 

[kwired]

The op said it was Homeline but I guess like Dennis said the neutral has nothing to do with it. I thought how a Gfci trips with a shared neutral but a 2 pole is designed to work that way.

But will trip if the protected neutral is faulted to ground or if neutral from another circuit is somehow tied into it, which could easily happen if the two circuits are occupying same switch or junction box.

 

[electricalist]

Yep. Mr Kwired you're right, I hate when I second guess myself. 3 way switches are notorious for that back in the day. 12-2 for travelers leaves no neutral. I'd check the arc fault neutral for current with the afci breaker off

 

[mopowr steve]

All neutrals are tied together with a multiwire branch circuit--how else can it be done but a DP afci should work fine with it. The thing is you have to isolate the problem. Disconnect one leg from the breaker and see what circuit the problem is on. Then go from there but remember an afci- if that is the cause of the trip- needs 4 or so amps before it will sense the fault. GE and perhaps Seimens are the only manufacturers that have taken the gfci out of the breakers. I am not sure about seimens but a member here says that is the case. When I called Seimens they said that was not so but that guy seemed to not understand the question very well so I wouldn't trust his response.

What I mean to say, is it possible that a 3rd circuits neutral could be also connected to his MWBC neutral in a switch box somewhere? I may have to re-read his post to see if his MWBC extends beyond the bathroom. Maybe one of the circuits in the MWBC goes out to a hallway light switch location that may already have another circuits neutral present and that they were tied together