Question about GFCI trips in a 1970s kitchen rewire

I was working on a kitchen remodel in an old Portland bungalow last month. The homeowner wanted new outlets, so I started swapping the old ungrounded ones for GFCI protected ones. Every time I hooked up the fridge circuit, the GFCI would trip instantly. Took me 2 hours to trace it back to a tiny nick in the old NM cable where it passed through a floor joist, grounding out to a nail. I had to re-run about 15 feet of 12/2. Has anyone else found hidden damage like this when updating old kitchen wiring? What's your go-to move for checking the whole run before installing the new device?

2 comments

2 Comments

sagecooper2h ago

Ever think to just Megger the whole run first? I've been burned by that exact hidden nail damage before. My rule now is to test insulation resistance on any old cable before I even touch the outlets. A cheap meter that does a 500v test can save you a huge headache. It shows you a bad wire right away so you don't waste time swapping devices.

the_anthony1h ago

Man, that's such a good point... my buddy just went through this last month. He spent a whole day changing out every switch on a circuit in an old house, only to find the problem was still there. He finally borrowed a megger like @sagecooper mentioned and found a crushed wire in the wall. It would have shown up immediately with that first test. Now he won't even start a job like that without checking the cable itself. It seems so obvious after the fact, but you really do learn the hard way sometimes.

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