Spent a full day on a bad ground loop in a retrofit | Alarm System Installers

Charlie Black · 2026-03-26T18:50:07.874756+00:00

I was doing a panel swap in an old house in Tacoma last week, upgrading a 90s system to something modern. Everything powered up fine, but the keypad kept throwing a ground fault error. I figured it was a quick fix, maybe a stray wire. I spent the next 8 hours checking every connection, running a new ground wire to the water pipe, even isolating the transformer. Turns out, the old installer had run the keypad wire right next to a line voltage cable for decades, and the insulation had basically melted together inside the wall. The induced voltage was just enough to trick the new panel. Had to fish a whole new home run. Has anyone else run into a sneaky fault like that where the cause was totally hidden?

cameronm476mo ago

My last one of those was a 1940s house in Ballard. The low voltage wire was stapled to the same stud as the main feed for the furnace. After seventy years, the jacket had just turned to dust. The new panel saw it as a direct short to hot. Took me two days to stop trusting the old wire map.

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mason_reed476mo ago

That kind of hidden damage used to seem unlikely to me.

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maxl936mo ago

Ugh, classic. The house just wanted one last prank before retiring that old wire.

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olivia_white934mo ago

Feel for you @maxl93, that sounds like a nightmare to trace. Old houses love hiding surprises in the walls when you least expect them. Hope the rest of your swap goes smoother from here on out.

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