When we inspect houses where an amateur has been doing electrical work, there’s a good chance we’ll find outlets with reversed polarity. This is when the neutral and hot wires are flipped around at an outlet or downstream from one. Reversed polarity creates a potential shock hazard, but it’s usually an easy repair. An inexpensive $5 electric tester will notify you if you have a three-prong outlet that is properly grounded. If you have a three-prong outlet that is not grounded, however, your electrical tester won’t be able to tell you if the polarity is correct or not.
A brief definition of Hot and Neutral wires: On a standard outlet, technically called a duplex receptacle, there are two wires that carry electricity. The grounded conductor is the wire that is connected to the ground, or earth. This wire is often referred to as neutral wire and should always be white. That’s what the larger slot on your outlet is for.
The other wire doesn’t get connected to the earth, and it’s called the ungrounded conductor, or hot wire. This wire can be any color besides white or green, but it’s usually black or red. That’s what the smaller slot on your outlet is for. Because the hot wire completes a circuit by coming in contact with the earth, if you touch a hot wire and you’re in contact with the earth (which is pretty much always), you’ll become part of the circuit. In other words, you’ll get shocked.
Some plugs have polarization to make them safer. This means that the one blade is bigger than the other so the larger blade can only fit in the neutral side.
Shock hazard scenario #1: I’m toasting an English muffin and it gets stuck in my toaster. I look in the toaster and see that the heating elements are off, so I assume it’s safe to stick a knife in the toaster to get my muffin. Because the switch that regulates the flow of electricity to heating elements in the toaster shuts the hot wire off, I should feel safe doing so. My toaster plugs into an outlet with reversed-polarity. The switch on my toaster shuts off the hot wire. This means there is always power at the heating elements. Dope will stick a knife in the toaster and electricity will travel through the knife, my body, then back to the earth. Breakfast is ruined. Your mom was right to tell you not to do this even if your toaster is on.
Shock hazard scenario #2: I’m using an old trouble light, and my finger accidentally comes in contact with the outside of the metal socket that holds the light bulb in place. The socket is always connected to the neutral wire, so no big deal… unless the light is plugged into an outlet with reversed polarity. In this case, I’ll get a shock. If this happens while I’m laying on the garage floor working on my car, there’s a good chance that I’d be electrocuted. It can also happen to old table lamps with exposed metal sockets.
How to fix: Get an electrician. I want to say that the fix is as simple a swapping the wires at the outlet, but that’s not always the case. If the wiring is correct, the error occurred somewhere upstream from where the outlet is located. The electrician will need to trace the wires and find the problem. It would be unacceptable to simply swap the wires at an outlet.
Reversed polarity at outlets can be a shock hazard. However, electronic equipment that is plugged into an outlet with reversed-polarity will still work. Don’t assume that your outlet is wired properly just because it “works”. You can test for reversed polarity at your outlets with an inexpensive outlet tester you’ll find at any home improvement store.
If you have outlets with reversed-polarity, an electrician can repair.
