Test for Grounding

You can test a grounded, three-slot receptacle for grounding (remember, the power is on) by placing one probe of your tester in the short slot and one in the hole for a plug’s grounding pin. The short slot is for the hot wire. The bulb should glow to indicate that the receptacle is grounded. If it doesn’t, keep one probe in the grounding hole and place the other one in the longer, neutral slot. In this position, if the bulb glows, it shows that the receptacle is grounded, but the black and white wires have been reversed (they’re attached to the wrong terminal screws) and should be corrected. If the bulb doesn’t glow in either case, the receptacle isn’t grounded. A three-slot receptacle that isn’t grounded is misleading and dangerous to a user. It might indicate that only the individual receptacle is incorrectly wired or that it was inadvertently used to replace an ungrounded receptacle. Either way, you want to know so you can correct the problem.

Check and Check Again

Receptacles, like switches and fixtures, need to be checked with a voltage tester before you do any work on them. The test is similar for both grounded and ungrounded receptacles, except you’ll be testing for grounding as well with the former. A grounding test can only be done with the power on.
With the power off, insert both ends of your voltage tester into the slots of the receptacle. The light in the tester should not go on. If it does, the power has not been turned off, or the wrong circuit was shut off. Even if the tester bulb does not light up, you can’t be sure that the current is off. The receptacle might be damaged but still receiving a current. Remove the cover plate and carefully pull the receptacle out. Place one probe on the brass terminal, which should be connected to the black or hot wire. Place the other probe on the silver or neutral terminal. You must touch both terminals to complete the circuit. The bulb shouldn’t glow if the power has been shut off.

Disreputable Receptacles

Receptacles are pretty long-lasting, but old ones eventually can give out when the clips no longer hold a plug snuggly. There also are drawbacks to some old receptacles if they’re neither polarized nor grounded. Receptacle bodies also get broken if furniture or toy trucks somehow bang into them. (This happens at gyms all the time, only barbells do the damage.)
You want your receptacles and their cover plates to be intact. Broken or missing sections can set up you and yours for a shock or worse. When replacing an old receptacle, you can’t simply pop a new, grounded receptacle into an existing two-slot outlet. It doesn’t work that way, although there is a trick you can do with a GFCI that will give you some protection, but it will not ground any equipment plugged into the receptacle. A GFCI does not give grounding protection unless a grounding conductor already is present.