Editor’s Tip: You conduct most of these tests with the power on, so work carefully. To be safe, hold both meter probes in the same hand so that a shock doesn’t pass through your body.

How to Measure Voltage

Set a multimeter to measure voltage. Insert a probe into each slot and read the line voltage measurement. A properly working outlet gives a reading of 110 to 120 volts. If there is no reading, check the wiring and the outlet.

How to Check for a Properly Grounded Outlet

A properly grounded outlet registers voltage when one probe of a voltage detector is inserted into the small outlet slot and the other probe is placed on the receptacle’s center screw. If the light fails to turn on, the outlet is not properly grounded and you should conduct a polarity test.

How to Test the Outlet

Before you begin, turn off the power. Then disconnect the outlet from the wiring. Set your multimeter to ohms and put a probe into one of the outlet slots and the other probe on the nearest terminal screw. The meter should indicate continuity. Test the remaining slot and terminal. Then test the ground slot to the grounding terminal.

How to Test the Outlet

When two cables enter a box, one leads to the breaker or fuse box; the other carries power to other devices on the circuit. To determine which is the hot cable, turn off the power, disconnect the outlet, and place caps on all the wires except one black one. Turn the power back on, and touch a probe to the ground wire or the box and the other probe to the black wire. If you get a reading, it is the hot wire. If not, it is the wire leading to the other devices. To double-check, turn off the power, move the cap from one black wire to the other, turn the power back on, and test the uncapped wire.

How to Conduct a Polarity Test

Insert one probe into the large slot and the other against the screw (scrape off any paint to insure a good contact). If the voltage detector lights, the hot and neutral wires are reversed. If the light doesn’t light with the probe placed in either slot, the wiring should be checked further.