Reverse polarity is when the hot and neutral wires on a receptacle/outlet are wired “backwards.” In other words, the hot (black) wire is where the neutral wire should be, and the neutral (white) wire is where the hot wire should be. This results in a shock/electrocution hazard.
Reversed polarity is also sometimes referred to as a hot/neutral reverse.
Receptacle wired with reversed polarity
Why is Reversed Polarity Dangerous?
Avoiding reverse polarity is important because with a reversed polarity outlet, 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 stop 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.
In the diagrams 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.
Now let’s look at the situation of reversed polarity.
The diagram below shows what happens in a situation with reverse polarity.
When you have the same lamp plugged into a receptacle with reversed polarity, it can create a very dangerous situation.
It is dangerous because the 120 volts are now connected to the wire that would normally be the neutral wire. This means the lamp components are now energized – even when the switch is open.
(Again, everything in red in the diagram is electrically energized.)
This time, if you were to stick your finger into the light socket even with the switch off, at a minimum you would get a painful shock. Worst case – you could be electrocuted.
Another example showing the danger of a reverse polarity outlet 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.
How many of us have ever had to dig a piece of bread or frozen waffle out of a toaster?
Imagine if someone sticks a knife into this toaster plugged into a receptacle with reversed polarity. It is possible for that knife to touch something that is energized and to potentially electrocute him or her.
How Do I Know if My Outlet Has Reversed Polarity?
To test a receptacle for reversed polarity, you will need an outlet tester or a non-contact voltage detector.
These are inexpensive and can be bought in almost every home improvement store, stores such as Walmart, or online on sites such as Amazon.)
You plug the receptacle tester into a receptacle/outlet as shown below, and it will have lights indicating if the receptacle is properly wired or not.
In the picture below, the image on the left shows what the different light combinations indicate. The image on the right is showing what this tester will show on a receptacle with reverse polarity. (Different testers may have different light configurations.)
Using a Non-Contact Voltage Detector
The photos below show two different non-contact voltage detectors. They look similar to a writing pen.
To use it, you must first turn it on by pushing the on/off button.
All you need to do to test for voltage is the bring the tip of the tester near the wire or slot in the receptacle that you want to test. There is no need to touch it to the live/hot metal as you do a multimeter.
If voltage is detected, most of these testers will illuminate a red light and will make a chirping noise. (Read the specific instructions for your device.)
If no voltage is detected, the light will normally remain green.
The photo below shows a typical receptacle.
The wider (taller) slot on the left is the neutral slot.
The more narrow (shorter) slot on the right is the hot slot.
The roundish slot below is the ground slot.
Voltage on narrow slot
No voltage on wide slot
No voltage on ground slot/hole
Checking Receptacles for Reverse Polarity
When you use a non-contact voltage detector to check for reverse polarity, it does NOT matter if the receptacle is grounded or not grounded.
All you need to do is to stick the tester into each slot of the receptacle. If you get the indications shown in the photos above, then you will know that the receptacle is not wired with reversed polarity.
On the other hand, if you detect voltage in the wider slot, and no voltage in the narrow slot, then the receptacle is wired with reversed polarity.
NOTE: You cannot check for proper grounding using a non-contact voltage detector. This is because the grounding slot/hole will indicate no voltage whether the receptacle is grounded or not grounded.
Will Reverse Polarity Damage My Appliances?
It is possible that some appliances and some electronic equipment can potentially be damaged if they are left plugged into a receptacle with reversed-polarity.
The presence of voltage on the wrong side of a circuit or circuit board will cause some devices on the board to remain energized even when the device is turned off. This can possibly result in damage to some circuitry.
How to Fix an Outlet With Reverse Polarity
Fixing a reverse polarity situation is a fairly simple process.
Steps to correct a receptacle with reversed polarity.
- Turn off the power to the receptacle by shutting off the correct breaker.
- Remove the receptacle cover.
- Remove the receptacle from the wall.
- Remove the black wire from the silver screw and remove the white wire from the gold screw.
- Attach the white wire to the silver screw.
- Attach the black wire to the gold screw.
- Replace the receptacle into the wall.
- Re-install the cover onto the receptacle.
See our blog post on How to Fix Reversed Polarity for more details or watch our video below.
NOTE: If you discover that the black wire is already attached to the gold screw, and the white wire is already attached to the silver screw, but the receptacle is indicating reversed polarity by one of the test methods mentioned above, then there is a problem someone upstream of the receptacle in question. In this case, you will need to do some additional investigating or contact an electrician. It is not the purpose of this blog post to cover every situation.
Summary
In this post, I have attempted to explain the dangers of reversed polarity, how to determine if a receptacle has reversed polarity, and how to fix a receptacle with reversed polarity. I hope that this explanation and these diagrams help you to understand the dangers of reversed polarity and how to correct it.
© 2022 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.
