1954 House with original (cloth over rubber) wiring on the main floor. Replacing fan and light with simple overhead light fixture and toggle switch with a dimmer switch. Box has an incoming conduit and an outgoing conduit. When I pulled out the toggle switch, one screw had a dark wire and the other screw had two dark-colored wires attached.
Box Contents: 2 green (ground) wires nutted together, 2 white (neutral wires nutted together), and 3 dark-colored wires (one is hot, two are not).
After installing the dimmer and capping off the other dark-colored wire, my bathroom and hallway lights were out. When I tried to connect the third dark-colored wire to the switch, reinstall and turn the power back on, the circuit broke.
I figured out that this was a switch loop, removed everything, looked for signs of frayed wires, tried to organize as much as possible, pigtailed the ground wires, pigtailed the hot/bathroom/hallway wire, re-nutted everything, taped around the edges of the nuts, and turned the power back on without putting the switch back in the box. Everything worked fine.
When I added everything back to the box and tried to screw it down, the circuit popped. I turned it all off and waited a day thinking that maybe I had fried the dimmer the first time.
Tonight, I re-inspected and connected to a regular single pole switch. With the power off, I put the switch in the box, screwed it down and then turned the power back on. The hallway light turned on, but when I hit the switch on the GCFI lightswitch/power combo in the bathroom, the circuit broke again. When I removed the switch from the box and tried again, all of the lights and switches work.
Can the electrical box be bad? Any ideas?
This is in a plaster/lathe wall and is not able to be pulled or easily cut out. Does it sound like I have a short in one of the wires and its only happening when put into the box?