Warning: Do not try this at home, at work, or anywhere else. You could get electrocuted.
They say necessity is the mother of invention, and I guess they're right. I inspect a lot of old houses in Minneapolis and Saint Paul that still have two prong outlets, and testing these outlets has always been much more time consuming than testing three prong outlets. I started thinking about this the other day, and ended up inventing a silly looking electrical tester that will save me a couple seconds at every two-prong outlet I test.
Until my invention, testing a two-prong outlet required two hands and multiple steps with a standard two-lead tester. Here's how it went:
Stick one lead in each slot – if the tester lights up, the outlet is energized.
To test the polarity of the outlet, I stick one lead in the smaller slot and grab the other lead. I'm not kidding. If the polarity is correct, I'll at least see a very small light at the tester. If my body is in contact with a grounded surface, the light will actually light up quite brightly. If the polarity is reversed, the light won't light up.
At this point, you're probably thinking that the second part of this process is a stupid test because I could get shocked. Technically, yes, I'm getting shocked, but there is so much resistance in my tester that I can't even feel it. If I'm standing on a concrete floor with wet feet and I try this test, I can feel a very slight tingle. That's about as bad as it gets… but I'm sure this would also make someone from Underwriters Laboratory laugh maniacally if I tried to get my little invention listed.
I've invented a tool that rolls these steps in to one, and only requires one hand. I took a standard three prong tester and cut the grounding pin almost all the way off. I attached a stranded copper wire to this pin, and then wrapped my electrical tester with foil tape. That's it, that's all.
When I plug this tester in to a two-prong outlet, the middle light will light up if the outlet is energized.
If the light on the right dimly lights up while I'm touching the metal tape on the tester, I know the polarity is correct.
If the light on the left lights up, the outlet has reversed polarity. That's it, that's all. If I want to know if the outlet box is grounded, all I need to do is touch the box with skin while holding the tester; if the outlet is grounded, the dimly-lit light will get really bright.
How cool is that?