By Paul Bianchina
Q: When I bought my house, the home inspector said some of the electrical outlets had reverse polarity. He said it was not a big deal, but that to meet the building codes the outlets needed to be fixed. He said it was a simple repair, but I don't remember what to do. I was also wondering if I can do a few at a time, or if they all need to be done at once. --Matt A.
A: Electrical outlets have three slots in the front: the shorter rectangular slot is designed to be the hot conductor, the taller rectangular slot is the neutral conductor, and the U-shaped slot is the ground. For this polarity to be correct, when the outlet is connected to the electrical wiring in the wall the hot wire (typically black) is connected to the brass-colored screw on the outlet, the neutral wire (white) is connected to the silver-colored screw, and the ground wire (green or bare) is connected to the green screw.
Reverse polarity occurs when the wires are connected to the back of the electrical outlet in reverse order - black to the silver screw, white to the brass screw. It's not an uncommon mistake, even in brand-new houses, and since the outlet still works in this condition there is no way to really catch what happened unless you're looking for it. As the home inspector said, this does not really present a danger, since household appliances are designed in such a way that a polarity reverse cannot present a safety hazard. There are, however, some sensitive electronics and surge protectors that could potentially be affected, and I agree that it's a good idea to make the correction.
If you are comfortable with electrical wiring, you can easily do the work yourself - it should take less than five minutes per outlet, and they don't all need to be done at once. Purchase a plug-in tester from any retailer that sells electrical supplies. Plug the tester into the outlet and read the sequence of lights on the front, which will indicate whether the polarity is incorrect, and also whether or not the outlet is properly grounded. Identify which outlets need to be corrected and shut the power to the outlets you want to work on. Use the tester to also confirm that the electricity is off.
Remove the cover plate and remove the outlet from the box. Unscrew or unclip the wires from the back of the outlet, then reattach them to the proper terminals. Reattach the outlet and cover plate, reactivate the power, and check the outlet with your tester to confirm both power and correct polarity.
If you are not comfortable with electrical wiring, if you're unsure at any point how to proceed or if you notice anything about the wiring that causes you even the slightest concern, contact a licensed electrician and have them inspect and correct the problem.
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