Reverse Polarity in Home Wiring

Reverse Polarity is a common problem I come across either in the outlets or with the home’s wiring. Home wiring is color coded, Black is HOT (often called the live wire) and WHITE is NEUTRAL. This is different from 12 volt systems where the black is often the neutral, it is very important to understand how wiring differs for a home over an automobile.

In home wiring it is very easy to know what the wires are:

  • White wire is the neutral
  • Green or bare wire is the ground
  • Any other color than white, green or bare is a hot (live wire)

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An outlet that is wired backwards is a reversed outlet, the terminals on a outlet is colored to let you know what is the hot side and what is the neutral. Brass is hot (black wire) the silver is neutral (white wire). If an outlet has reverse polarity is it hard to tell unless it is tested because alternating current (AC) will only travel in one direction like water flowing in the river. If it was hooked up to direct current (DC/12 volt battery) the motor would rotate in the opposite direction and is very easy to recognize.

The reason that reversed polarity can create a shock hazard in certain situations is because the switch is positioned before the hot wire side enters the appliance and the neutral is connected to the other end of the appliance circuitry, when the polarity is reversed the appliance circuitry is electrically charged all the time, but only functional when a switch closes the neutral wire connection and the current begins flowing.

Using the diagram of a toaster below I can show you the difference in a correctly wired and a reversed polarity outlet. The left toaster is wired correctly with the circuit being live only up to the switch. The right toaster with reverse polarity has all the wiring live up to the switch. With the toaster reversed if you were to put a knife or fork into it you would get shocked. This also works for a light bulb socket, the metal shell would become electrified and cause a shock if touched. If the wiring is correct it is harmless to touch a lamp shell or stick something in a toaster.


Reverse polarity needs to be repaired and is usually simple, most of the time just switching the wiring around. If you are comfortable working with electricity it is a easy DIY project, if not call a licensed electrician. If the whole home wiring is reversed then the services of a licensed electrician will be needed.

The only way to know if your wiring has reverse polarity is to test it, the easiest and simplest way to test is to purchase an inexpensive three light circuit tester at any hardware store.



Bad Upgraded Outlets

Inspecting older homes the most common defect I find is bad electrical outlet upgrades. Usually the outlets are upgraded by homeowners or other non-qualified person to do electrical. The following is the verbiage I use in my report.

“At some time the electrical outlets have been upgraded from the original 2-prong outlets to modern 3-prong outlets without upgrading the wiring to the outlets. This presents an unsafe condition. The purpose of the third prong is grounding.”

Installing a 3-prong outlet on a 2 wire system is wrong and not up to any codes, but is happens in many older homes. The purpose of the ground is to provide an alternate path for the electrons to flow back to the main electrical panel. If there should be a short, the electrons do not have an alternate path back to the electrical panel without the grounding wire.

When your home has bad upgrades as a homeowner you have four choices:

  • Upgrade the wiring to new grounded wire
  • Install GFCI (ground fault) protection
  • Install new 2-prong ungrounded outlets
  • Know the 3-prong outlets are not grounded and use as a 2 prong outlet with no ground. This condition needs to be disclosed to anyone using the outlet. The 3-prong outlet will give a false sense of security about the outlet being grounded.

If you use non-grounded outlets I recommend using a good quality surge protector for sensitive electronics. ( Desk top computers, flat screen tv’s, ect..)

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