Recently I was having a problem with a couple of outlets in the garage and was seeing odd behavior with some appliances plugged into a couple of outlets. The same devices worked well, correct, on the other outlets in the garage.
So, I thought I should post the info for customers and dealers. This is a very basic electrical test that all should know how to do.
A typical 120v home outlet has three wires. Normally the colors are used to tell which wire is hot=black, neutral=white, and ground=green. It is possible however that a panel or junction box gets crossed up and thus these wires are not what they appear. So, then they get wired into an outlet by visual color, but actually are reversed.
Typical Correct; black wires HOT, to dark colored screws on side of smaller vertical slot, white wires NEUTRAL, to silver colored screws on side of longer vertical slot, if green wires GROUND, they go to green screw and tie into the center round hole.
To determine correct polarity, you will need an AC/DC Multimeter. This tester is just 2 leads attached to a digital readout with a dial in center usually. These can actually cost an arm and a leg, or you can get them for just a few bucks online if you look around. I would never pay over $20 so look around. To check each outlet with this multimeter tester...
(1) Put 1 lead into the small vertical slot and the other lead in the big longer vertical slot. You should get a lite or volt/amp reading if all is correct.
(2) Next, put 1 lead in the small slot, and 1 lead into the ground hole (the round one) and you should get a lite or volt/amp reading if all is correct.
(3) Last, put 1 lead in the big vertical slot and 1 in the ground hole, you should NOT get a lite if all is correct.
The problem could begin somewhere upstream from the outlet, all the way to the breaker panel. To find the source of the problem each outlet and connection has to be verified this way. Eventually you should find one that doesn't lite the tester as it should. When you find it, check that outlet from the proper colored wire to the proper colored screws.
THIS IS A DANGEROUS ISSUE:
As we work with electricity, we have to respect the danger of injury and potential fire. I try to teach others to know about electricity, but to be VERY respectful, careful, aware. The danger is that someone could be working on power with the assumption that all is wired correct, to color codes. NEVER assume that. Please always use your meter, learn how to use it on basic tests. Check all wiring with it before you do anything, verify voltages, amps, polarity, etc, and just take your time. The more basic your level, the more time and caution to use.
If you find that the AC polarity of a component needs to be reversed, usually it's just to change the polarity on the outlet itself. Please do not attempt this if you are not comfortable working with line voltages and be absolutely certain the breaker is off and there is no voltage at the outlet! If getting correct polarity means putting wrong colors to wrong sides.. off standard color coding, just call an electrician and my advice would be to fix the circuit and restore that all color coding to polarity is correct.
No Short Cuts On Wiring Should Ever Be Employed. If You Need an Electrician, Call One. If Something Isn't Right, Fix It. Always Go THe Best Quality And Safest Route With Your Circuits and Home Wiring.