while work crew was here removing solar panels from roof (don’t worry they’re going back on when the new roof is done) a 15 Amp circuit started tripping its breaker immediately. the circuit goes to the furnace/AC-blower.

even when i disconnect the blower the circuit trips immediately.

the solar guys say “not me” since they don’t touch the indoor breaker panel.

anyone have ideas what could cause something like that?

i was leaning towards the breaker being bad, but i decided to poke around.

turns out there’s one power socket in the rafters. i guess for a work light — and that’s where the 18V transformer for the thermostat lives.

turns out it was just shitty electrical. the transformer conduit shorted with a very blackened socket screw.

once i separated them it was A OK 👌.

nearly touching for 15 years. the roofers must’ve jiggled it enough to make contact.