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Reuben Saltzman

Reversed Polarity Outlets

When I inspect houses where an amateur has been doing electrical work, there’s a good chance that I’ll find outlets with reversed polarity.  This happens when the hot and neutral wires get flipped around at an outlet, or upstream from an outlet.  Reversed polarity creates a potential shock hazard, but it’s usually an easy repair.

Reversed Polarity 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’, so this wire is called the grounded conductor.  This wire is commonly referred to as the neutral wire, and it should always be white.   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.   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.

Knife in ToasterShock 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.

Trouble Light

Damage to electronic components?  No. I’ve heard that reversed polarity can cause damage to some electronic equipment, such as computers… but that’s not true.  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 – they cost about $5 at any home improvement store.

If you have outlets with reversed polarity, you should have the wiring repaired by an electrician.

Reuben Saltzman, Structure Tech Home Inspections – Email – Maple Grove Home Inspector

No responses to “Reversed Polarity Outlets”

  1. Chris Ruston
    May 7, 2009, 6:55 am

    Some corrections are in order here. With alternating current both wires, white and black, are equally “hot”. The third slot on some recepticals is the only one connected to the earth.
    The white wire is connected to a common bus in the circuit box and therefore is often referred to as the “neutral” wire. This is really a misnomer because it is not neutral. Because of this one should NEVER put a fork in a toaster that is still plugged in regardless of the polarity of the receptical. The fact that the white wire is connected to the common bus necessitates that the polarity of the wiring is consistent throughout the house. Electricians have arbitrarily chosen the white to be the common “neutral”.

  2. Reuben Saltzman
    May 7, 2009, 8:08 pm

    Chris – I debated posting your comment because most of what you have to say about this matter is just plain wrong, and I don’t want to give any readers the wrong impression, but I also don’t want to censor any comments other than spam… so I posted your comment. If you’re writing this as a practical joke, good one. You got me.

    Some corrections are in order here. With alternating current both wires, white and black, are equally “hot”.

    True, they’re both equally “hot”, but the ungrounded conductor is the one that is commonly referred to as “hot”, because there is potential between it and the earth.

    The third slot on some recepticals is the only one connected to the earth.

    That’s just plain wrong.

    The white wire is connected to a common bus in the circuit box and therefore is often referred to as the “neutral” wire.

    It’s called the neutral because it is a grounded conductor, and there is no potential between it and the earth.

    Electricians have arbitrarily chosen the white to be the common “neutral”.

    That’s just plain wrong.

  3. jenny
    May 8, 2009, 1:50 am

    i got a very bad shock the other day while i tried to clean my toaster with a knife while it was still plugged in. nice tips

  4. Top Ten Home Inspection Defects For Old Houses | Reuben's Home Inspection Blog
    October 27, 2009, 5:14 am

    […]  Improperly Wired Outlets Ungrounded three-prong outlets and outlets with reversed polarityare very common defects.  These are shock hazards.  You can check the outlets in your own home […]

  5. Ground Fault Circuit Interrupters (GFCIs), Part 1 | Reuben's Home Inspection Blog
    November 3, 2009, 6:04 am

    […] a quick refresher. In my blog about reversed polarity outlets, I explained that there are two wires that conduct current – one get connected to the earth […]

  6. Maureen McCabe
    November 3, 2009, 6:40 am

    I came from your ActiveRain post on Ground Fault Circuit Interrupters, which I am going to Re-Blog, probably later today. Thanks.

    I like the way you handled Chris’s comment. He got one thing right though…

    “one should NEVER put a fork in a toaster”

  7. Reuben Saltzman
    November 3, 2009, 7:06 am

    Maureen – thanks for reading. I agree about the toaster, I pulled the plug before taking a picture of that!

  8. Philip Parkinson
    April 28, 2010, 8:03 pm

    Hi, As an electrician I am still amazed that people put metal utensils into a pluged in electrical device. If it is still plugged in expect the the damn thing to be HOT (and not hot as in warm). It should be common sense to unplug a device before you operate on it. Philip

  9. John B
    April 27, 2012, 12:37 pm

    You are wrong about RP not affecting electronic devices. In a computer setup, if the CPU is plugged into one circuit that has RP, and other connected equipment such as printer, router, etc are on a normal circuit, and there is a neutral-ground fault somewhere, you can fry your stuff.

    Also for some reason a lot of professional photography flash equipment doesn’t like RP.

  10. Reuben Saltzman
    April 28, 2012, 5:02 am

    John B – it would be the neutral-ground fault causing a problem, not reversed polarity.

  11. jeff perry
    July 16, 2012, 4:09 pm

    Was using a sawsall today to cut old copper water pipe which wasn’t grounded to anything. While cutting, the blade made contact with the new copper pipe (grounded). An arc occurred & i got shocked. The outlet showed hot / neutral reversed. Another outlet on a different circuit ( hot/neutral wired correctly) was used and no arc or shock. Could my shock be caused by the wires being reversed? The first circuit has problems: 15 receptacles on it. The first (3) show correct polarity; after an attic connection, all downstream have the hot/neutral reversed. This was done by a bone head electrician. I know I can reverse the wires but there must be something else going on. First time reading your blog. I’m from So. Calif

  12. Karl Fife
    November 5, 2012, 1:17 pm

    Not to be nit-pick, but this really needs to be said:

    The ONLY place where the neutral wire is truly “neutral” (in the sense that it has no voltage potential with respect to ground) is AT the bus bar IN the panel where it is directly bonded to ground. Everywhere else along the circuit, there is a voltage potential between neutral and ground. The voltage varies depending upon how much current the neutral is carrying at that moment, and how far you are from the panel.

    Example: Presume you have the maximum 15 amps of current coursing through a 14 AWG copper wire. Perhaps ‘cramming’ would be a better word because 15 amps is literally the maximum that the wire can carry without potential safety concerns. The main idea is that there IS RESISTANCE to this flow, especially when the wire it’s “maxed out” as above. This resistance creates a voltage potential between the neutral wire and ground, which means there is a potential for being shocked.

    I like to think of electricity going through wires using an analogy of fluid in the hoses of a hydraulic circuit. If you measure the pressure just ‘downstream’ of the place in the line were the ‘work’ is being done, there will still be SOME pressure in the line. If you poke a hole in the return line, SOME amount of fluid will squirt out (analogous to an electric shock, providing an alternate path to ground). The amount of the fluid leakage depends on the pressure at that SPECIFIC spot in the line, which is determined by how fast fluid is being crammed through the line, and the remaining distance to the non-pressurized reserve tank. More importantly (and to take the analogy further), if the return line gets ‘pinched’, impeded or blocked on its way back to the reserve tank (analagous to a flakey, bad or open neutral), the pressure at the hole can jump to the maximum line pressure!

    Circling back to electricity, the voltage potential (to ground) on the neutral wire is usually MUCH less than 120V, and it varies based on the load and the distance from the panel, and it can potentially spike to 120V under certain circumstances.

    This is one of the major reasons for the dedicated ground wire. The dedicated ground is not normally carrying any current, thus has zero voltage potential to ground. Hopefully the ground wire will be ready to bear enough current (to ground) to prevent enough of voltage potential (pressure) to ground, to prevent your body from looking like an attractive enough “detour”. Hopefully this will work well enough to prevent a harmful shock.

    If you’re still keen to win a Darwin award, and roll the dice by putting a metal object into your toaster, be sure to accidentally touch the heater element closer to the side that touches the neutral wire. In theory your shock should be less intense. Move progressively closer toward the hot side if you want to liven things up.

  13. Mark McCarthy
    November 30, 2012, 8:46 pm

    I was working on a range where the control kept flashing. I replaced it. New one kept flashing as well. Found the outlet had reverse polarity. Told the guy to have a licensed electrician fix it. He said it worked fine for years and he wasn’t going to fix it. I found a good outlet and plugged in the range. Worked beautifully. Reverse polarity affects appliances. Not sure if this falls under “electronics” or not. Just wanted to throw it out there.

  14. Reuben Saltzman
    November 30, 2012, 8:54 pm

    Mark – I have to think there was more than just reversed polarity at that outlet. That might be all that a basic tester was telling you, but I’d be willing to bet the voltages at that outlet were off as well.

  15. Deb IBEW Electrician
    December 29, 2012, 12:32 pm

    The neutral is used to carry the unbalanced load (electricty) in a 120 volt circuit. So depending on what is plugged into, and being used in that circuit at any given time, there could be enough voltage to give someone quite a jolt. If it happened to cross the body, going through the heart, it could be fatal.

  16. Gilbert hewko
    February 17, 2013, 6:03 pm

    Replaced my motor on my furnace,shut off switch above furnace.rubbed a wire against motor blew the 15 Amp breaker.only way to shut off furnace power I find is at the breaker.took cover off switch box white wires are hooked to pole switch.fan on motor will shut off with switch but wires remain live.i think I put that switch in years ago.checked all the switches I put in and black are tied together.is this my problem.also my breaker goes quite often now if the washing machine is going.motor was new and had a furnace repair person hook it up for me.last comment he said was I think your wiring hooked up wrong.

  17. Reuben Saltzman
    February 18, 2013, 5:04 am

    Gilbert – it definitely sounds like your wiring is hooked up wrong, but I can’t tell exactly what the problem is from your description. I recommend you have an electrician fix it.

  18. Sean
    February 25, 2013, 11:54 am

    We recently moved into an older house. There is a problem with one of the rooms which has 4 sockets and another room with two other socket on an adjoining wall that do not work at all. When we had an inspection done the report stated that these sockets were simply reverse polarity but will work. (the inspector made so many errors that we asked for, and got, our money back so long as we promised not to complain officially)…

    Do you know what might be wrong here? I have tried using electrical items that require polarity and those that don’t (differentiated by whether or not that have different sized prongs) and nothing works in these sockets. There is wiring going into the boxes.

    Please go easy on me – I’m from the UK and the socket wiring in the US is VERY different.

  19. Reuben Saltzman
    February 25, 2013, 1:26 pm

    Hi Sean, there is a long list of potential reasons for items not working at the outlets. I’m sure you’re rather try to fix this yourself, but I think you would be much better off hiring an electrician.

  20. Luke Stoltzfus
    August 9, 2013, 11:54 am

    This blog is very helpful and informative. I finally understand why there is a second dedicated wire for ground, usually green or bare. Since both white and green go to the same ground terminal in the panel, I didn’t understand the increased potential in the white wire to the earth with every added appliance going upstream. Now I get it. Thank you.

  21. Jeff
    October 24, 2013, 2:29 pm

    Reverse polarity is no more dangerous than any other outlet. When’s the last time you heard of a house fire or worse, an electrocution death from reversed polarity? Never. I’m an inspector with numerous electrician contacts that all verified my statement. I also contacted my HI course instructor. Same thing.

  22. Reuben Saltzman
    October 24, 2013, 2:33 pm

    Hi Jeff,

    I recommend you ask your electrician contacts and your HI course instructor what the purpose of a polarized plug is. Please, do get back to me.

  23. Jeff
    October 26, 2013, 11:15 am

    If dangerous then Why is a three prong into a two prong adaptor an approved electrical connection? These adaptors do not have a small paddle versus large paddle port. The idea of reverse polarity being hazardous is over kill. In f t as a HI we do not test the older two pronged outlets, nor do we record them as a defect. Think about if. If it was a hazard a HI would be required by state reglation to demand they be replaced with three prong outlets or the house would fail inspection. In ending, please reply with a verifiable report of any incident that has occurred regarding a reversed parity outlet. I can’t find one.

  24. Reuben Saltzman
    October 26, 2013, 1:43 pm

    If dangerous then Why is a three prong into a two prong adaptor an approved electrical connection? These adaptors do not have a small paddle versus large paddle port.

    That’s not true. Even these adapters are polarized, meaning one of the blades is larger than the other, to help prevent reversed polarity. I’m sitting here looking at one right now. I encourage you to stop by a home improvement store and take a close look at the adapters.

    In f t as a HI we do not test the older two pronged outlets, nor do we record them as a defect.

    Speak for yourself. http://www.structuretech1.com/2010/08/two-prong-outlet-tester/ I test them, and if I find reversed polarity, I recommend correction.

    If it was a hazard a HI would be required by state reglation to demand they be replaced with three prong outlets or the house would fail inspection.

    You lost me there. I’m not aware of any states that have regulations demanding homeowners correct anything identified by home inspectors, and I’ve never heard of a house ‘failing’ an inspection. Home inspections are not ‘pass/fail’.

    If you’re brand new to this industry and you’re trying to get to the bottom of whether this is really a serious issue, I applaud you for that. I meant it when I encouraged you to ask your electrician contacts and your HI course instructor what the purpose of a polarized plug is. The short answer is that it’s a safety device designed to prevent people from getting electrocuted. You obviously won’t take my word for it, so please, have a chat about this topic with someone you trust.

    In ending, please reply with a verifiable report of any incident that has occurred regarding a reversed parity outlet. I can’t find one.

    If you need a body count to be convinced that this is a hazard… well, I guess I just won’t convince you.

  25. Matt
    November 3, 2013, 2:31 pm

    On the question of reverse polarity and electronics I don’t believe you can make a blanket statement about the result will be, without knowing how the electronics are handling power conversion and how the ground reference is established. Most electronics with a switching mode supply are polarity independent, but that is not the case for all electronics.

  26. Reuben Saltzman
    November 3, 2013, 2:40 pm

    Hi Matt, then insert “As far as I know” at the beginning of that section.

  27. Matt
    November 3, 2013, 10:07 pm

    Thanks. This is a very heated topic as I’ve seen from discussions around the internet. 99% of the time I don’t think reverse polarity would cause a problem to consumer electronics because the first stage is normally a rectifier which is non-polarized. Some specialized electrics, with an earth-referenced power supply (where the neutral is earthed at the power supply) might not be so safe. That’s not likely to be present in most homes. I’ve just been investigating a house fire where half the home was reversed, which caused some unusual damage (although did not start the fire).

  28. dk
    December 4, 2013, 9:11 am

    Reuben — as usual I find your topics both interesting and informative.

    What I find real interesting, at times, are the comments. In this blog some of the comments are especially interesting and dare I say, just plain wrong. Wow !!

    Many people don’t have any understanding of electricity, period. Then there are those that *may* have a rudimentary knowledge of Direct Current and think it applies to Alternating Current used in our homes. All of which leads to so much misinformation, incorrect thinking and implementation leading to dangerous situations.

    Your explaination of basic electrical, and the reversed polarity subject is spot on.

    As you stated the *neutral* ( grounded ) conductor is indeed at the same electrical potential as the *ground* ( grounding ) conductor. While they both terminate at a main electrical panel at an electrically same potential they serve two different purposes — which is why grounding conductors are not tied to a neutral bus and visa versa.

    The *neutral* ( grounded ) conductor is considered a normal current carrying conductor since it connects directly to a load. Whereas, the *ground* ( grounding ) conductor is not directly connected to a load . Therefore it is not a normal current carrying conductor and it’s purpose is to only carry fault current to *ground* safely.

    Some comments are really interesting …

    Deb IBEW Electrician —- says … “The neutral is used to carry the unbalanced load (electricty) in a 120 volt circuit.”

    No, that’s not the purpose. The *neutral* conductor is part of the path for AC current flowing to & from a load. I would like to know how the load is unbalanced other than a ground fault ?
    In which case an *unbalanced load * from a ground fault isn’t caried by the neutral conductor.
    This is misinformation coming from a supposed electrician.

    Jeff the home inspector — really should consider a different line of work.
    The governing bodies that oversee all electrical devices , fixtures and installations have specific rules pertaining to conformity. This would include reversing polarity at receptacles. Codes are very specific from the manufacturing of the receptacles and to how they are wired. If they are not wired correctly — that’s a code violation. Of which I would expect a home inspector to recognize this basic violation.

    As for reversed polarity affecting electronic equipment , that’s a non-issue. Consider the majority of electronic equipment is Direct Current based , the power supply conversion is done after a transformer secondary stage. Which results in isolation from the primary Alternating Current side where polarity has no affect.
    I can’t think of one electronic device that is referenced to the incoming AC lines.
    Case in point take an older device with a two prong non-polarized plug — it can be plugged into a receptace in any orientatation and still function normally.

    The only exception would be a GFCI device of which it’s designed purpose is to be polarity dependant.

    These are just some examples of the lack of knowledge and mis-information running rampant — unfortunately the internet magnifies this.

    The scarey thing many of these unknowledgable people are doing their own electrical or advising others on what to do.

    Keep up the good work Reuben.

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