What did they do here?

[Robert Jones]

Two white feeds and I have no idea what the "u" shaped black wire is doing? This was feeding a jetted tub. 100 amp system.

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[Jim Port]

The 2 whites are the GFI pigtail and the circuit neutral.

The U might be part of an older GFI design. I have seen this on old Cutler Hammer GFI breakers.

[Richard Moore]

I have never seen one like that but I suspect Jim is right regarding it being an older design GFCI. It looks like the lug screw of the U-loop has been filled in at the factory with black goop or plastic. My guess is that the loop is an external hot feed to the GFCI circuitry. Hell, it might be one of the very first GFCI breakers, an original attempt, and worth a small fortune as a collector's item (Fabry will buy anything old).

I would have tested it by pushing the button and checking that the tub was then off. And then, to cover my ass, I would likely have reported it as an older design that I have never seen before, and one that was worth replacing to be on the safe side.

I had a 50's home today with a bunch of very old style GFCI receptacles. A couple no longer responded to the test button. I'm recommending replacing all of them, including the ones that did work, with new units.

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