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[bkenobi]

I wasn't able to find any listings for the module with pictures until just now.

https://www.ebay.com/i/301748032907

The link will die, so these are the pictures from their listing.

[Noam]

I think I found something that might explain it, here: https://www.ericson.com/wp-content/uploads/2015/08/How-a-GFCI-works.pdf

It looks like it might be designed to kill power in the event of an open Neutral - with an intact Ground. Since a portable cord has a much higher chance of being damaged (as opposed to a GFCI mounted in a wall box in a home), and since the GFCI can't protect from a short to ground without the Neutral in place to measure against, the relay kills the power if either the Hot or the Neutral are damaged between the breaker and the outlet (like by nicking the cord with a saw).

[bkenobi]

That explanation sounds reasonable.  I'm not sure how it works in practice, but damaging a cord is obviously more plausible when they aren't armored by a wall.

Btw, the link is dead for me.

[Noam]

That explanation sounds reasonable.  I'm not sure how it works in practice, but damaging a cord is obviously more plausible when they aren't armored by a wall.

Btw, the link is dead for me.

Sorry, I fixed the link. It should work now.

[bkenobi]

Thanks for that!  It doesn't explicitly say they are using a relay inside their portable GFCI devices, but knowing that mine is wired that way it does make sense how that could solve the problem of an "open neutral".

[Noam]

Thanks for that!  It doesn't explicitly say they are using a relay inside their portable GFCI devices, but knowing that mine is wired that way it does make sense how that could solve the problem of an "open neutral".

I found a patent document describing using a relay to protect against an open neutral condition, which is what I based my search on to find this one.

[bkenobi]

I especially liked the "shocked" user on that pdf.