A tiny metal sliver on the inside of my index finger

Do they really use 1200 ohms ? That seems a bit low. I think you would want the thing to be more sensitive than to trip at 100 mA.

In practice it's more than that. I originally wrote 100 ohms but I figured then somebody would say "the resistor would blow up". I *think* the GFCI trip current is down around 10 mA or so in practice. It can't be zero because we live in an imperfect world, and because Y capacitors exist.

I also think that GFCIs exist with different trip current settings; the ones that are sold for household use have a relatively low one, while I've read that you can get ones with a higher setting for specialized applications. I've never held one of those in my hand, though.

Matt Roberds

I got some good advice at the trade counter of a plumbing shop a few years back it ammounted to "you're supposet to know that, don't ask me, ask a plumber"

That's not correct. The test button has to work even on an ungrounded circuit. It connects a resistor from the line side of the GFCI to the load side, one end to the neutral and the other to the hot, through the test switch.

Ed