I finally figured out why that old panel kept tripping on sunny afternoons

Got a call about a breaker popping every day around 3 PM at a house in Tempe. Checked all the usual stuff, load, connections, nothing. Then I noticed the main feed from the meter ran right under a metal roof overhang... the sun was heating that conduit up for hours, expanding the conductors just enough to cause a short in an old, brittle section of insulation inside. Had to reroute about 15 feet of conduit into the shade. Has anyone else seen heat from a structure cause a fault like that?

3 comments

3 Comments

wesley18115d agoMost Upvoted

That's a stretch, man. Old insulation fails on its own all the time, you just got lucky finding it after moving the conduit.

xenaf5115d ago

Actually, Joel's thermal expansion idea makes a ton of sense. That slow creep over years is a real thing, especially with older wiring that gets brittle. It's not just random luck finding it, moving the conduit probably revealed a problem that was already building up. Seen similar stuff where heat cycles cause just enough movement to create a short over time.

joel_martinez15d ago

Absolutely, thermal expansion on a hot roof can push old wires right into a metal box edge. I found a cooked 12/2 in an attic where the nail plate was gone and the sun baked the sheathing soft. The copper had slowly crept into contact over a few summers.