I live in a condo built in the late 70s. I'm installing a ceiling fan in the master bedroom and need to run electricity to it. I went in the attic and there is an existing romex wire near the location of the fan that I thought I might tap into. I turned off the master bedroom circuit breaker to see if that wire was on the bedroom circuit, and the wire was still live. To make a long story short, I turned off and on each circuit in the house, and nothing killed the power in the wire! I finally find out that I had to turn off the master bedroom circuit breaker, and also the circuit breaker for the den next door in order to get the non-contact voltage tester to stop beeping. All the lights and outlets in the bedroom and den behave as expected (when I turn off the bedroom circuit breaker all the bedroom lights and outlets go off, and when I turn off the den circuit breaker all the den light and outlets go off).
So why is this wire in the attic controlled by two circuit breakers? Is this normal? I believe it's a typical 12-2 wire (all wires in house are 12 gauge). Are both wires (black and white) hot? Bad idea to tap into this wire (adding a junction box) to run electricity to my future ceiling fan?