Reverse polarity occurs when the wires of a building's electrical system are connected to the wrong terminals of an outlet. If the wires of an outlet are reversed, there is the possibility that the electrical current may damage appliances and electrical motors. At the least, electric-powered appliances malfunction when polarity of an outlet is reversed. The worse case scenarios are a shock or an electrical fire. Fortunately, testing for reverse polarity is simple. With a polarity tester and the accompanying voltage chart, you can test the polarity of an outlet in a few minutes.
Plug the outlet tester into the outlet. Make certain the number of prongs match the number of prong holes in the tester. Do not use a two-prong tester for a three-prong outlet. Make sure the tester is designed for the voltage of the electrical system. For example, do not use a 110-volt tester for a 220-volt circuit.
Observe the pattern of the lights on the tester. A three-prong outlet tester has three lights: one for the hot wire, one for the return wire and one for the ground. Compare the light pattern with the chart supplied by the tester's manufacturer. If the polarity is correct, all three lights of most testers illuminate.
Test several sockets in the building to assure the tester is operating properly. If the same pattern shows up on the tester repeatedly, each indicating a reverse of polarity or a failed ground, there is a chance one of the bulbs on the tester has failed. If this is the case, replace the bulb or the tester and check the outlets again.