The 5 Essential Outlet Tests Every Homeowner Should Know How to Do

When electrical issues arise, these quick receptacle power tests will come in handy. Learn how to measure voltage, conduct a polarity test, and more.

Ever wonder if power is actually reaching an outlet? The voltage reading on a multitester or multimeter can tell you. When properly used, a multimeter also can tell you whether the white and black wires are reversed, whether the receptacle is properly grounded, and which cable entering the box feeds power to the outlet. If you don't have a multimeter, you can use a voltage detector in place of the voltmeter and a continuity tester ($6, Home Depot) in place of the ohmmeter. If a problem arises with an electrical receptacle in your home, you can usually diagnose it by running one of these outlet tests.

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.

measuring voltage in outlet

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.

testing polarity in 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.

testing voltage in removed outlet

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.

voltage detector determining hot cable

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.

red and black probes polarity test in outlet

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.

Frequently Asked Questions

  • What is a multimeter?

    A multimeter measures multiple electrical properties, including voltage, resistance and current.

  • Are multimeters and voltage testers accurate?

    The accuracy of either a multimeter or voltage tester will depend on the quality of the instrument you use. It's better to pay a little more for a product that works well.

  • Are multimeters and voltage testers the same?

    A multimeter will test volt levels, amps, and ohms, while a voltage tester only tests to see if voltage is present.

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