Receptacle tester
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A receptacle tester or outlet tester is a device used to verify that an AC wall outlet is wired properly. The tester itself is small device which looks like the "plug in" end of a power cord, with several lights on it rather than an attached cord. Although a multimeter could be used to perform a series of tests which would give the same results, an outlet tester can perform the entire array of tests by simply plugging the device into the outlet once and observing the state of the lights. The tester performs several tests at once but the tests themselves essentially fall into two categories: tests which determine that the outlet actually functions and tests which determine that the outlet is properly wired for safe operation.
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[edit] Tests performed
[edit] Functionality
The most basic job of the outlet tester is to verify that the outlet actually provides power to a device plugged into it. In order for an AC outlet to be functional it must have, at a minimum, a live or "hot" connection to a varying electrical voltage, and a neutral connection to complete the circuit. If either of these is not hooked up, or is damaged in some way, then the outlet will not function at all. The voltage between these two connectors also needs to fall within a certain range for proper operation, however many outlet testers only check for the presence of voltage across the proper connectors, not the actual level of voltage, which can easily be checked with a multimeter.
[edit] Safety
The much more important role of the outlet tester is to not only verify that electricity is present in the outlet but that the outlet is properly wired, with each plug being connected to the proper wire in the building's wiring. There are two primary reasons for testing this. First, some devices must have a specific prong connected to the live connection or damage to the device could result. Second, and more importantly, if the live wire is connected but the neutral or ground wire is not, a dangerous situation could be created by preventing safety mechanisms from operating properly. Furthermore the ground wire is typically attached to the case of an electrical device as a safety precaution to carry away current if the insulation on the wires is damaged and the case becomes charged. Although this is an important safety feature on many devices, if the outlet is improperly wired with the ground plug connected to the live wire the safety mechanism has the opposite effect and charges the outside of the device creating the potential for an electric shock for anyone touching the device.
