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Reversed polarity is when the hot and neutral connections at a receptacle are wired “backwards.” Wiring is color-coded, and the black wire is “hot,” meaning that it is electrically energized, normally to about 120 volts. It is sometimes called the “live” wire. It will shock you if you touch it. The white wire is called the “neutral” wire. It completes a circuit by providing a return path of the electrical current back to the breaker panel. The neutral wire is at zero volts and will not shock you under normal circumstances.

Why is Reversed Polarity Dangerous?

Avoiding reversed polarity is important because with reversed polarity, a shock hazard can be created in certain situations. Let me explain why. Let’s look at the example of a lamp plugged into a correctly wired receptacle. When the lamp is turned off, the 120 volts from the receptacle stops at the switch. This means that you can unscrew the light bulb and replace it with a new one and there will be no power to the light socket. (Please do not try this, but you could theoretically stick your finger into the light socket and not get shocked.) Look at the diagram below. The part of the circuit in red is the only part of the circuit that will be energized when the switch is open. This makes the rest of the circuit safe.

properly wired receptacle- reverse polarity

Look at the diagram below. When you have the same lamp plugged into a receptacle with reversed polarity, it can create a dangerous situation. This is because the 120 volts are now connected to the wire that would normally be the neutral wire, so the lamp components all the way to the switch are now energized –  even when the switch is open. The reason the bulb is not on even with power inside the lamp is because there is no return path for the current to flow back to the receptacle until the switch is closed. In the diagram below, everything in red will be electrically energized when the device is plugged into a receptacle with reversed polarity.

reversed polarity diagram

Another example showing the danger of reversed polarity would be something such as a toaster. If the toaster is plugged into a receptacle with reversed polarity, then many of the components inside the toaster will be energized even when the toaster is turned off. Imagine if a child sticks a knife into this toaster. It would be possible for that knife to touch something that is energized, so this is definitely a safety issue. I think many of us have had to use a knife to dig a piece of bread/toast out of a toaster. This is also an electrocution hazard if that toaster is plugged into a receptacle with reversed polarity.

I hope that this explanation and these diagrams help you to understand why a receptacle with reversed polarity creates a potentially dangerous situation.

© 2020 Mike Morgan

This article was written by Mike Morgan, the owner of Morgan Inspection Services. Morgan Inspection Services has been providing home, septic and well inspection services throughout the central Texas area since 2002. He can be reached at 325-998-4663 or at mike@morganinspectionservices.com. No article, or portion thereof, may be reproduced or copied without prior written consent of Mike Morgan.

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