Originally Posted by thekctermite
Seems to me that when the light is switched on there's a "leak" of current to something somewhere within that circuit. Could be an arc somewhere in the wiring, could be a bad switch, could be a low quality switch.
Might be a wild goose chase but it might be worth swapping the switch(es) whose use is causing the AFCI to trip with new ones. That would at least rule them out.
I'm an old hat when it comes to residual earth leakage circuit breakers, having BUILT heavy Industrial "switchboards" & motor control centres, distribution mains etc., as a "FULLY REGISTERED Industrial Electrician - since 1985... so.
the quick answer is VERY VERY simple.
On the circuit in question..."SOMEWHERE" there is a direct fault "short_circuit_ to earth - between NOT a phase LIVE - but ALL connected Neutrals (A common problem - MOST often overlooked even by fully registered sparkies - unfimiliar with these devices)
Basically, I would strongly suspect rodent damage - somewhere inside Ur attic, or even a wall cavity..
AS this can be a very "difficult fault to pinpint & trace.. I would strongly suggest - wherever YOU reside- to go & thumb through your local service directory- & GRAB an electrical contractor - whom will HAVE the specialist tools, testing equipment & replacement cables.
Oh & P.s. any "out_of_balance" between current passing IN via a live line - MUST come OUT through the same circuit breakers neutral - or it WILL always "trip".
(which is exactly as this is doing.
SO - IF you are a home handyman - as I suspect... DO NOT stuff around with your life... as any illegal repair work COULD BE LETHAL.