Tips for Using a Voltage Tester
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Tips for Using a Voltage Tester

How to use a voltage tester to check that a circuit is off and how to check receptacles for polarity.

Performing your own electrical repairs is rewarding and a great way to save money, but working with household current can be dangerous. The most important thing to remember when doing electrical work is to turn the power off. Electrocutions kill an average of 143 construction workers each year. More than half the electrocutions of electrical workers were caused by direct or indirect contact with live electrical equipment and wiring, including lighting fixtures, circuit breakers, control panels, junction boxes and transformers. This is why it is so important to verify that power is off by using a voltage tester.

When shopping for a voltage tester look for an Underwriters Laboratories (UL) listing and a Category III rating, which means the tester will not melt down in the event of unexpected high voltage.

How to Test Loose Wires

1. Check the tester’s body, probes, and wires for signs of wear. Turn on the tester, cross the probe tips, and shake the wires. The continuity light and some testers have a buzzer so that you know voltage is present even if you can't see the LED. Lastly, check the tester on a known live circuit. If the tester does not work consistently, have it repaired or replace it.

2. Never use your fingers to hold probes on loose wires. Put a wire nut on the end of loose wires, and place the probe in the wire nut. Make sure wires are free of oxidation, glue, or oil to avoid incorrect readings.

3. Use an alligator clip on the neutral if you’re checking voltage at several points, such as several hot wires to a neutral wire. This allows you to pay attention to the probe placement while checking the hot wires.

Voltage Check - Unlike plug-in testers, probe testers verify voltage both within the slots of a receptacle and on side terminals. Place one probe on the neutral, longer slot, first, then on the hot, shorter slot. The tester should read 120v. Remove the probes in reverse order. Hold the probes back from the tip to avoid shock if a wire moves or your hand slips.

Receptacle Test -  Check for obvious problems in a grounding (three-hole) outlet by placing the tester’s probe in the two vertical slots. The tester should read 120v. A properly grounded receptacle should read 120v with one probe in the shorter slot and one probe in the grounding hole. (See below) If these tests show no voltage, either power is not present, or the neutral or ground wire is disconnected or absent.

Polarity Test- Tools, appliances, and fixtures are designed so that power comes in on one of the two wires in a power cord. Reversing this arrangement, called polarity, can result in harmful shocks. Check for correct polarity by placing one probe in the grounding hole and the other in the shorter, hot slot. The meter should read 120v. Remove the probe from the hot slot and place it in the neutral slot. The meter should read 0v and also show continuity. Reversed readings mean that the polarity of the receptacle is reversed.

Phantom Voltage

In some instances you may read a voltage between hot-to-neutral of 50v even after you have turned off the circuit breaker. Typically if the circuit is de-energized, it should read 0v or if the circuit is mislabeled and still on, the tester should read 120v. You may be getting a false-positive reading, known as phantom voltage. Phantom voltage is caused by a live cable that induces a harmless voltage on a parallel de-energized cable. The simplest way to get a true reading is to use a solenoid-type tester. A few solenoid-type voltage testes are Etcon VT154 Audible Voltage Continuity Tester and Fluke T2 Voltage and Continuity Tester.

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