• Scott Wells

Reversed Polarity



Last summer I was inspecting a home in Almaden Valley that was very well constructed. I was hard pressed to find anything wrong at all until I found a receptacle in the living room that was reversed polarity. Hah! Finally something I can put in my report!


What is a receptacle with reversed polarity? Let’s back up just a bit to go over some basic electrical concepts.


Wall receptacles for modern homes are connected to 3 different wires that can be identified by different colored insulation. The insulation colors are usually black (for the hot wire), white (for the neutral wire), and bare copper for the grounding wire. Take a look at the faceplate of your receptacle and you will see two slots and a hole (unless you have an older electrical system with only two slots). Often the slot on the right is a bit smaller than the other slot. This smaller slot is connected to the ungrounded or hot conductor, which is the black wire that provides AC (alternating current) power to the receptacle. The other slot is attached to the white neutral wire which provides an easy return path for the power to ground (or more accurately to it’s source). Electricity always want’s to return to it’s grounded source. That hole below the slots is for the bare copper grounding conductor, which doesn’t really do much during normal operation. This grounding conductor provides an emergency “back up” path for current to help protect your homes electrical system and computers etc from getting fried in the case of a big electrical surge like a lightning strike.


For electricity to become useful to us, it requires a closed loop in order to discharge it’s energy. Now if you put an electrical load within that loop (think of a light bulb) the electricity will flow from it’s origin at the power station through the black hot wire, through the light bulb and then continue through the white neutral wire. The current is not going in one direction, but is alternating back and for the really fast, perhaps 50 or 60 times a second. Now say you hold a hot wire in one hand and a neutral in the other, YOU become the light bulb and the current flows through you. Not an experience you want to try, as it can take very little current to be lethal.


Now in the case of reversed polarity the neutral and hot conductors have been wired incorrectly – the hot wire was attached to the neutral slot in the receptacle and the neutral wire attached to the hot slot.


Now lets say you plug in your toaster to this incorrectly wired receptacle and toast some sourdough for breakfast. Nuts, the slice has jammed into the toaster! So you flip up the lever on the toaster and see the heating elements go from orange to dark and you think the power going into the toaster is off. However, with a reversed polarity receptacle, you inadvertently have turned off the neutral wire instead of the hot wire, so there is still electricity present the heating elements even though they have gone dark. You insert a knife into the toaster which contacts the metallic heating elements in the toaster. Now ZAPP! You become the new neutral wire and current seeks to return to ground by flowing through the knife and through your body. If you are unlucky enough to be standing in your bare feet and the floor is a bit damp from recently being mopped, then current will flow through you, giving you a shock or even worse. Even if you are standing in your shoes on a dry floor you may feel a tingling sensation as you hold that knife. That is why you should always unplug your toaster before retrieving a stuck piece of bread.


The solution? Call a licensed electrician. Repairing reversed polarity is easy and usually just a matter of switching the hot and neutral wires.


See you next time -

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