Its an easy test and yes I have done it. Take a bad power head and to make it worse nick the hot wire next to the pump and drop it into a bucket of water, pick one, salt or fresh. Plug the pump into a new GFCI receptacle. DO NOT STICK YOUR HAND IN THE BUCKET! When it doesn't trip drop a grounding probe in. I used a 10 gallon tank for our local fish club with a glass lid to make sure no one put their hand in to show others how dangerous water and electricity can become. That was one of the dumbest test I did when I was young and dumb. It hurt like hell being barefoot and on a tile floor. Guess what? The GFCI didn't trip when I got shocked, it did when I dropped the grounding probe in.I beg to differ. While that 5mA is swimming around the tank or following some other path it's not returning on the neutral. As I said a GFCI monitors for an imbalance between the hot and the neutral it doesnt care were that current is, only that its not where it's supposed to be. I've only been an inside wireman for 12 years.
If a gfci device doesnt trip it is either wired incorrectly or it's a faulty piece of equipment.
