The outlet tester checks that each contact in the outlet appears to be connected to the correct wire in the building's
electrical wiring. 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, electrical safety (which requires impedance testing),
insulation breakdown voltage, or loop connection of
ring mains. Simple three-light testers cannot detect some potentially serious house wiring errors, including neutral and ground interchanged at the receptacle. There may be a "
bootleg ground", where the neutral and ground pins have been connected together at the receptacle, which cannot be detected either. A quick supplemental screening test for these simple miswiring errors can be performed using a non-contact voltage tester (NCVT) or
non-contact voltage detector. ==History==