January 08, 2018

Wiring Fun

So, we own a new house. Today I added a new outlet in the basement, to bring power close to our treadmill. There was an overhead outlet in the middle of the basement, which had a hanging florescent fixture plugged into it. The other three overhead florescent fixtures were plugged into switched outlets, but this one was always on. Unsurprisingly, the bulbs in that fixture were almost burned out, but I digress.

Before I began wiring I checked that the outlet I was going to pull power from, was properly wire. My tester showed all clear, including the ground. Excellent. I added the new box and outlet, ran the wires back to the existing overhead outlet box, unplugged the florescent fixture's power cord from it, opened it up… and discovered that there was no ground wire to be seen. Instead, a short shunt connected the outlet's ground screw to its neutral side. (Not even a neutral screw, the bare copper wire was plugged into the outlet's friction wire inlet.) This was mysterious. My outlet checker has three LEDs, had I failed to read them? Surely it wouldn't be fooled by a ground connected to neutral?

I made a new plan- I'd remove the ground-neutral shunt wire, ground the wire from the new outlet to the (metal) junction box, wire the old outlet's ground to the box too, then tomorrow head to the hardware store and get a couple of feet of insulated single conductor and a plumbing ground clamp. The ground in this house is the water inlet, and there was a pipe just a foot away. In fact, that pipe was what the florescent fixture was hanging from. I'd wire the outlet as is, and tomorrow connect the box to the pipe to ground everything nice and proper.

So I wired as planned, except as noted I didn't have the wire to ground the box. I closed it back up and turned the circuit breaker back on, then tested both outlets, new and old. As expected, both were good except for being ungrounded. Leaving my outlet tester in one plug of the old outlet, I plugged the florescent fixture back in so I could see better to put away my tools. As soon as I plugged the light fixture, the outlet tester switched to showing a proper ground.

I rubbed my eyeballs and scratched my bald spot. I unplugged the fixture and the ground indicator LED turned back off. After a little cogitation and I realized what the dickens was happening. That florescent fixture is hanging from the plumbing, you may recall. It was hanging by two lightweight steel chains. The florescent fixture's metal shell must be grounded, so when I plugged it's three-prong plug into the outlet, the whole system was properly grounded through the power cord to the fixture shell to the steel cables to the plumbing.

As you might imagine, this is shady as all get out and I'm still going to run a proper ground wire to firmly connect to the plumbing. But I'm now amused by the craziness that happens with older houses.

Posted by: Boviate at 10:20 PM | No Comments | Add Comment
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