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Discussion Starter #1
Our 2nd Floor has an Arc Fault Circuit Breaker in the panel and it occasionally was tripping, but now it's been pretty consistent when I have the vanity lights, over both sinks and the makeup vanity turned on. This is on a 3 way switch and each fixture holds 4 40watt bulbs. It is a 15amp circuit.

I've done a load calc on this circuit and I believe I'm well under. The bathroom has a total of 3 circuits (a 3-4 bulb track light with either CFL or LED in it), a Heat Lamp (winter I run 2 150watt Heat Lamp Bulbs in summer 2 100w equivalent LEDs) and then these vanity lights (3 4bulb fixtures each running a 40watt Incandescent bulb). Also on this circuit, I believe, is a bedroom 3 bulb fixture with 60watt incandescent bulbs. The office with 2 bulb fixture with 75watt equivalent LEDs and then the stairway which is a 3 bulb fixture with 40watt equivalent LEDs. ***Only when I turn on the vanity lights does the breaker trip.

I had one of the vanity bulbs burn out recently and it might have still been in the fixture when this started, but I eventually pulled it out. Then I tested it with some bulbs out and some bulbs in. At first it wouldn't trip right away, then it started tripping, seemingly no matter which bulbs were in or out.

I have now installed LED bulbs in about half of the fixtures and at first I got a lot of flickering, but eventually that stopped. One or two might flicker for a minute, but I question if those bulbs are wearing out.

Were do I start trouble shooting this? Is it likely the incandescent bulbs are going bad? For the most part those bulbs have been in these fixtures since we moved in 9 years ago and we use this bathroom daily. Or is it possibly the fixtures, which I believe were installed during a reno in the 80's or maybe even the 3 way switch(s)?

I have resorted to pretty much just leaving these lights turned off and I haven't had an issue, even since a couple days ago when I installed the half dozen LEDs into the fixtures.

I don't mind replacing the switches and eventually I plan on replacing the fixtures as I plan on updating this bathroom in the next year or two. I suppose if I need to pull them apart and check them I can do that as well. I just can't seem to figure out which piece is causing the issue. I have had a bulb that was going bad cause the arc fault on the main floor bedroom circuit trip when the bulb started flickering, so I'm leaning towards it just being a bulb, but when dealing with about 12 bulbs that gets tricky.
 

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This could take a loooong time to find. I'd start with the simplest to fix: If
your panel has another AFCI breaker, swap them. This will let you know if
it's the breaker or the cct..
 

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QUOTE - [ One or two might flicker for a minute,]
SHOULD NOT BE HAPPENING !
Dodgy/dirty switch maybe ?

It seems not all electronics get on well with AFCI breakers,
maybe some weird incompatibility issue ?
 

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Discussion Starter #4 (Edited)
Now when one 3-way switch(switch A) is flipped on or off the lights do as they should and go on/off, BUT if you flip the other switch(switch B), then they flicker and or don't even come on.

I figured switch B would be bad, so I went and got a new switch today, pulled the old one out and put a new one in, wired exactly the same. I run down flip the breaker on and go flip switch B and nothing, then I flip the switch A and nothing. I run back down flip the breaker off, go back up and pull it from the wall. All the wiring checks out in the, so I remember that flipping switch B caused the A not to work. You guessed it, I flip the breaker back on and it's performing EXACTLY as before, but no flickering yet.

Is it likely that switch A, which appears to work fine is the culprit? Or is there likely something else going on? I thought about putting the switch I replaced from switch B into A's position to see if that fixes it, but wonder if I'm wasting my time. Do I just go buy another switch and have both be new and see?

This really seems like when a 3-way is wired wrong, BUT as I said, everything has worked fine since buying this house back in 2008, so unless a wire has an issue somewhere. Is that even possible??
 

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Discussion Starter #6
I did and so far no flickering and both switches seem to work correctly. Very odd. I realize a switch can go bad, but looks like the issue is solved for now. I even added a few of the incandescent bulbs back in to see if they'd trip the arc fault and so far so good.

No clue how much of a safety hazard a failing switch poses, but it is kind of nice to see things working to protect.
 
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