1. Correct Wiring. Do not use the push-in type connections; they are not reliable. Instead, always use the screw connections

2. Reversed polarity. A receptacle that's "wired backwards" will work, but current flows in the opposite direction. This may cause a shock to someone fiddling with a device they know to be turned off.

3. Open Neutral. If the neutral is open, a plugged-in device will not work. If the receptacle is properly connected, trace the wire back toward the panel and look for a loose connection or a nail that has cut the wire.

4. Open Hot. If nothing lights up on the tester, turn the circuit off immediately; a loose or broken hot can start a fire. If nothing is obviously wrong inside the box, trace wire back toward the panel, looking for a loose connection or a nail that has cut the wire.

5. Open Ground. Always connect the ground wire when wiring three-prong receptacles. IF not connected, a person using a device with a three-prong plug may be shocked or electrocuted if there is a hot-to-ground failure inside the device. If there is no ground on the circuit, use a two-prong receptacle of a GFCI.

6. Hot and Ground Reversed. This could happen only on a circuit with one receptacle, otherwise the breaker would trip. But if this is the case, the frame of any device plugged into the receptacle would become hot, causing an immediate shock to anyone touching it.