The NEC clearly states that a two wire receptacle can be replaced with a GFCI. I did that, however, when i test the GFCI with a lightbulb load, hot to ground the GFCI does not trip.
I thought it was a bad GFCI, so i replaced and it still did not trip.
There's no "ground" for the current to "leak" to. If you used the test light from the GFCI protected hot, to the ground or grounded conductor of an extension cord, plugged into a grounded receptacle, the GFCI would trip.
You've got to watch those 2 wire GFI's when they have a metal cover. I stuck a bugeye tester in one and pressed the test button and that energized the faceplate. The GFI passed the trip test as I completed the path to ground because I was touching the faceplate.
Keep in mind that a GFI receptacle is not a cure all for 2 wire replacements. 250-114 has a list of equipment that is required to be grounded and a GFI on a 2 wire circuit doesn't provide the required grounding.
Few things are harder to put up with than the annoyance of a good example.
