In the example above, where the light fell in while a person was trying to open the top, consider the likely reaction of a person in that situation. It is likely that he would grab for the light to remove it quickly. Now, a person is in contact with the metal hood of the light and/or the water of the tank. Depending on what else that person is in contact with, you now have a fault path.
Brian in contact with what?
What in that room is both grounded and within reach?
But I was really talking about the GFCI helping the fish.
I suspect the 5 ma that humans can handle is a little tough on a gold fish or the cat.
