This happens when the hot and neutral wires get flipped around at an outlet. Reversed polarity creates a potential shock hazard, but it's usually an easy repair.
A brief definition of Hot and Neutral wires:
On a standard outlet, which is technically called a duplex receptacle, there are two wires that carry electricity. One of these wires is connected to the earth, or ‘grounded', and this wire is called the grounded conductor. This wire is commonly referred to as the neutral wire, and it should always be white (unless it's an old home with cloth covered wires). 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. 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.
Damage to electronic components? I've heard that reversed polarity can cause damage to some electronic equipment, such as computers. I researched that theory for this blog and I couldn't find any evidence to support it. Why would electronic equipment care which wire is connected to the earth? It doesn't. Reversed polarity is a shock hazard only. Electronic equipment will still function fine.
How to fix: Get an electrician. The electrician will check the color of the wires feeding to the outlet. If the white wire is connected to the smaller slot on the outlet, then the outlet was wired backwards. The fix is as simple as swapping the wires around on the outlet. If the wiring appears correct at the outlet, this means the white wire is now the hot, and a problem exists somewhere upstream from the outlet. This will take more investigation to determine exactly where the wiring went wrong. Simply swapping the wires at the outlet would not be an acceptable fix.
The bottom line is that reversed polarity at outlets is a shock hazard. Electronic equipment plugged in to an outlet with reversed polarity will still function properly. You can test for reversed polarity at your outlets with an inexpensive outlet tester. If you have outlets with reversed polarity, have this condition corrected by an electrician.
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