An outlet wired reverse polarity is a common mistake that I seem to find on a daily basis while doing home inspections. The correct way to wire an outlet is to wire the hot or black wire to the brass screw and the neutral or white wire to the silver screw. Another way to do it is to look at the face of the outlet, of the three prongs, there will be a smaller slot, a wider slot, and a rounded one above or below the two side by side slots. The smaller slot is the side for the black wire and the wider slot is the side for the white wire. If the outlet is wired reverse polarity, it is because the wires are on the wrong side of the outlet. This is common and generally an easy fix. Sometimes when I find one reverse polarity outlet in a house. . . . . I’ll find several more. They seem to travel in herds! What generally happens is that the amateur electrician changes more than one outlet in the house and if he or she gets one wrong, they get them all wrong. I guess it’s a 50/50 shot and they either wire them all correct or they wire them all incorrect. I once had a guy tell me that he didn’t know which way to wire them so he did half one way and half the other way. He said that he figured that at least half of them would be right! Now you see why us home inspectors always say to have a qualified electrician do any electrical work in your home.

The bad part about reverse polarity is that you can plug something in to it and it will work, even though it is wired wrong. You usually don't know the condition exists unless you look for it. Reverse polarity can be dangerous in certain circumstances, can damage equipment, and render an equipment ground ineffective. If you suspect your home's wiring is a bit shaky, or even if it seems fine, it's a good idea to check for reverse polarity. You can buy a simple circuit tester for around $10. Just plug it into all duplex receptacles; test them and determine if they are correct according to the lights on the tester. If you find any that are reverse polarity:

1) Shut off the breaker or pull the fuse that serves that receptacle (the tester's lights will go out).

2) Take off the cover plate from the receptacle, and use a voltage tester to be sure that none of the wires in the electrical box are still hot.

3) Unscrew or release the wires from the receptacle and re-fasten them to the proper terminals--white to the silver (neutral terminal) and black to the brass (hot terminal). The bare or green wire should connect to the green screw.

4) Put the cover plate on, turn the breaker back on, and test the receptacle again. It should test correct, if it doesn’t then call an electrician for further guidance.

What if whenever you take the cover plate off, you discover that the black and white wires are on the correct terminals? This means that the wires are incorrect at a junction box or at an outlet before the one that you are working on. If this occurs, you should call an electrician and let them correct the problem. I’m all for doing some repairs yourself, although reverse polarity outlets are done from someone that doesn’t know how to correctly wire an outlet. If they did, you wouldn’t be wasting your time trying to figure out how to fix it, right? As always with any home repairs, you should know your limitations and hire a professional to do the work that you do not know how to do. Need a contractor for your next home project? Be sure to check out the contractors section of this site to find local contractors that may be able to help you out.