Testing Electrical Receptacles

In this post, I will address how to test your home electrical outlets for the integrity of wiring. I will only address polarized receptacles with a ground that are found in modern or recently renovated homes. You can check the wiring of your outlets with an inexpensive circuit tester available for about $7 at your big box or local hardware store. Typically the testers have 3 lights that indicate that the wires are properly connected, not connected, or are improperly connected.

Some testers (like the illustration below) come with a GFI (Ground Fault Interupter) tester which is a button that, when pushed, creates a small short which should cause the GFI protection to turn off power to the receptacle being tested. But, the best way to test a GFI receptacle or a GFCI breaker (at the electrical panel) is not by using a receptacle tester but by pushing the integrated test button on the GFI receptacle or GFCI breaker itself. When the test button is pushed the circuit should "trip". It is then necessary to press the integrated reset button to reactivate the circuit.

Receptacle Tester

For the receptacle tester shown above, there is one red light and 2 amber lights. For a correctly wired outlet the red light will not glow and both amber lights will glow. Various combinations of lights on and off (shown on the label) will indicate various issues with the receptacle wiring. This type of tester will not indicate the quality of the ground, 2 hot wires in the circuit, or the reversal of grounded and grounding conductors. The last statement makes the tester seem pretty useless, but actually the tester will detect nearly all common improper wiring conditions.

What in the heck is a GFI?

A GFI is a device that is designed to shut off the flow of electricity if an electrical leak is detected. The GFI compares the current flowing out through the hot wire (black) to the current flowing out through the neutral wire (white). If the current flowing out through the white wire is less than the current flowing through the white wire, the GFI assumes that there is a "leak" and shuts off the circuit. This all happens quickly enough that electrocution can be prevented.

What does polarized mean?

With 120V circuits, the black wire is intended to be hot (called ungrounded) and the white wire is intended to be neutral (called grounded). If the two wires are reversed, the polarity is reversed. Why does polarity matter? Polarity matters with appliances that have switches. When an appliance is plugged into an outlet, the power should travel only as far as the switch. If there is a reversed polarity condition, the power will run through the entire appliance and back to the switch. A loose wire in the appliance could cause the appliance to be electrically charged which would be a shock hazard. Even though a device/appliance may function if the hot and neutral wires are reversed, it is potentially dangerous. After installing an outlet, the outlet should always be tested for polarity. If the tester indicates a reverse polarity condition, the outlet needs to be rewired.