Electrical outlet tester

It can identify several common wiring errors, including swapped phase and neutral, and failure to connect ground.

The tester confirms continuity and polarity of the electrical connections, but it does not verify current-carrying ability,[1] electrical safety (which requires impedance testing),[2] insulation breakdown voltage, or loop connection of ring mains.

[3] Simple three-light testers cannot detect some potentially serious house wiring errors, including neutral and ground interchanged at the receptacle.

[4] These problems can be detected with a multimeter and a test load, to verify that the ground connection is separate from the neutral and is not carrying normal circuit return current, or more typically by using a more-sophisticated multifunction tester.

[4] If a problem is thus identified, it can be investigated further using more-advanced equipment, or the outlet in question can be de-energized and disassembled for careful scrutiny.

A receptacle tester for North American wiring
A receptacle tester being used to check for some types of improper wiring of an outlet. For this particular tester, proper wiring is indicated by the two yellow lights.