# Why Reversed Polarity Is A Hazard

Any time  I inspect a house where an amateur has been doing electrical wiring in a home, there's a good chance that I'll find outlets with reversed polarity.  This happens when the hot and nuetral 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.

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.  I should be safe doing this, because the switch that controls the flow of electricity to the heating elements in the toaster shuts off the hot wire.  Unfortunately, my toaster is plugged in to an outlet with reversed polarity, so the switch on my toaster is shutting off the neutral wire instead of the hot.  This means there is always electricity at the heating elements just waiting for some poor sap to stick a knife in, and that electricity will travel up the knife, through my body, and back to the earth.  Breakfast ruined.  Your mom was right when she told you to never do this.

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 trouble light is plugged in to 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 this could be the last shock I ever get.  This can also happen with old table lamps that have exposed metal sockets.

Damage to electronic components?  No.  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.

Reuben Saltzman, Structure Tech Home Inspections - Email - Edina Home Inspector

Reuben Saltzman, Structure Tech Home Inspections

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18 Comments on Why Reversed Polarity Is A Hazard

MAY
02
2009
 I'm rather tolerant of home owners making their own repairs throughout their homes, except for electrical and plumbing matters. These trades are licensed for a reason and one of the reasons is safety. 7:02am • #1
 Great post, safety is #1 when it comes to electricity 7:27am • #2
 Ouch... My mother did tell us a kids to not do that, reading your post makes me glad she did! 8:05am • #3
 Hey Reuben - I am finding this all the time in the do-it-yourselfer finished basement. Could I get your permission to copy your post and included it in my inspection report when I find reveresed polarity? This is an excellent description of why it needs to be done right. 8:21am • #4
 All good advice. Thanks, Reuben! 8:31am • #5
 Very informative post. I've seen inspectors bring this topic up during inspections but didn't realize how serious of an issue it was if not corrected. 10:04am • #6
 Good post Reuben---these sorts of reversed polarity are particularly deadly if other parts of ones body is in contact with other grounded metal components---like the kitchen sink/faucet, case of refrigerator etc. 12:46pm • #7
 Dan C - go right ahead.  I'm going to include a link to this post in my own reports so my clients can read more about it. 12:57pm • #8
MAY
03
2009

Nice explaination Reuben, I may have to refer to this myself.

1:15pm • #9
JUN
03
2009
 That is the best explination I have ever heard, thanks Reuben 12:37pm • #10
 Tad, JJ, and Suzanne - thank you! 8:21pm • #11
JUL
12
2010

Re: reversed polarity and damage to electronic equipment--I'm not a professional electrician, but I've done my share of home wiring jobs. I was very careful to read, then read, then read some more before I started. Just once, I carelessly reversed the hot and neutral wires on a duplex outlet. I didn't know I'd made this mistake till I hired a pro to tell me why I'd fried a laptop computer and a flat-bed scanner (twice!) when I plugged them into this outlet. My pro friend found my mistake and corrected it. He told me that yes, reversed polarity "will fry your electronics." I sold that house a few days later, and I did not have opportunity to plug in my repaired laptop to test it. Even so, I'm doubly careful to wire my outlets correctly. I also check an outlet for polarity with a tester before I plug anything valuable into it!

 Lucas Hutton
8:06pm • #12
 Lucas - I believe your friend may have told you that, and I believe he believes it, but I would have to have some logical explanation of how reversed polarity could possibly cause damage to your equipment before I believed it. 9:08pm • #13
JUL
13
2011

Hi Reuben, would reverse polarity cause power tools not to work?  I just bought a home built in 1951 which has A 100 amps electrical panel.  Whenever I try to use a power tool, the power tool stops working after a few seconds.  I've had a couple of electricians come, and they both checked the power on the receptacles and both said that the power should be enough for the power drill and mytersaw, which sits on a 20a breaker.  Both electritians couldn't figure out why the power tools were dying.  The last electrician told me the receptacle I was using had reversed polarity.  The house is empty and the only appliance running is the fridge.  I've tried different power tools and have the same problem. I've tried plugging them to different receptacles on different breakers, but same problem.  Any ideas?

 Martha Rendon
5:00pm • #14
 Hi Martha,  reversed polarity would definitely not affect the operation of power tools.  Based on your description, you definitely have a wiring problem.  Have you see the electricians test the outlets using a multi-meter? 5:08pm • #15

The electricians checked different outlets with a multi-meter throughoutt the house and the voltage reading on all of them was between 118 and 120.  Besides the reverse polarity in one of them and no grounding on most of them, no other problems were detected.  All the appliances run without a problem.  It's only when I try to use a power tool that it seems that there isn't enough current to keep it going.  The electrician suggested putting a dedicated breaker and receptacle for the power tools, and I'm going with that solution, but I'd really like to find out what the main problem is.

6:25pm • #16
 Very odd.  I assume that none of these power tools cause problems at other homes? 6:37pm • #17
JUL
24

Try walking up and grabbing a common ground (as in a motor home, boat, etc) where there is a condition of reverse polarity.  This is where damage to electrical accessories is possible.

 Hank Terrebrood
10:53am • #18

What does the graphic say?
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