I got one of these many years ago when I would help out the residential part of the company. They seemed like the only way to test knob and tube or the old houses with switched neutrals back in the day. Any way I was also trying to figure out exactly what was going on so I was in the basement, touched a hot wire with the tester and it glowed dimly. I tried it again and touched a grounded pipe and it glowed very brightly. It's been quite a few years but I think it felt like a static shock on a cold dry day if you touch the grounded pipe during the test. My conclusion was that I was a parallel path to ground and haven't thought much about it since. I'm just thankful I gave up before I started jumping up and down barefoot in the kitchen and told the world.
