I'm in the middle of a garage/apt project and ran into an issue yesterday. Here's my layout.
I have a 200Amp service meter with two 100 amp breakers just after the meter....one breaker feeding the house and the other feeding the garage. The garage has a 100amp panel with a 60amp sub panel feeding an apartment above the garage. The 100amp garage panel is fed with 2 hots, a neutral, and a ground.
I have a 60amp 2 pole breaker installed in this panel to feed the 60amp apartment panel....2 hots, a neutral and a ground. I have two circuits wired from the 60amp apartment sub panel so far. One 20amp for some outlets in the apartment and a 15amp circuit for some lights in the apartment.
Yesterday, I had removed the 15amp light circuit breaker from the bus bar to do some work on that circuit. I pulled one of the light switches from the box and began to detach all my wires....suddenly there was a significant ARC that tripped the "main" 60 amp breaker feeding the sub panel.
This is concerning....i don't understand how the circuit still had power with the breaker disconnected physically from the bus bar. Any thoughts or insight? Any help would be appreciated.