Electricity: Electrical Testers and How to Use Them (Safely)


Continuity tester

You can work safer and track down problems faster using electrical testers.

Continuity testers (image on right). Electricians and homeowners alike find a good basic diagnostic tool in a continuity tester--a battery-powered device with a light-bulb, probe and alligator clip. The bulb will glow when you have a complete circuit. Check the tester by touching the clip to the probe. Use this tester to detect short circuits, open circuits or other problems in lamp sockets, switches, cords, and to see if a fuse is good. Never use a continuity tester on wires or equipment that are, or may become, energized. (read more)

Voltage testers. Equipped with a neon bulb and two probes but no battery, the 90- to 600-volt neon-bulb voltage tester lights up when voltage is present. Always check the tester's bulb in a known live receptacle before each use. Use it to detect voltage between hot and neutral, hot and ground, or two hot wires on 240-volt circuits. (read more)

Volt-ohm meters. These battery-powered tools, also called multimeters, test for continuity, AC and DC voltage and DC amps, and measure resistance (ohms). Some testers have digital readouts; others have a needle that sweeps across a dial. Choose one that measures 250 volts AC and has RX1, RX10 and RX100 settings to test resistance. Take time to read the owner's manual to avoid damaging the meter. (read more)

Caution: Always use a voltage tester to make sure that any switch, receptacle, circuit or appliance you are going to work on is really dead.


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Brand Name Manufacturers
Using a Continuity Tester

Using a Continuity Tester

Fuses. Touch ends of use with tips or probe. If fuse is good, bulb will light.

Lamp socket. Test for continuity between socket shell and silver screw, and center terminal and brass screw.

Lamp switch. Testing is similar to lamp socket (above) but switch operation can be checked.

Three-way switch . Operate toggle up and down with clip on common screw and probe on each traveler screw.

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a Voltage Tester

Using a Voltage Tester

Using a Voltage Tester

Test for power at receptacles. Check to deter mine that power to a receptacle is off before working on it. If bulb doesn't light, power is off.

Test for grounding with power on. Place one probe in short (hot) slot and the other probe to grounding slot or plate screw.

Test for power at switch. Set one probe on metal box and the other probe to each terminal.

Test hot wire in a metal box. Touch one probe to metal box and the other probe to each wire.

Three-way switch . Operate toggle up and down with clip on common screw and probe on each traveler screw.
Volt-Ohm Meter

Using a Volt-Ohm Meter

Be safe: read the owner's manual carefully to avoid damaging your multimeter. Rotate the switch to select the proper test function, such as volts, amps or ohms, before you start testing. Select a voltage or amperage range that's higher than the top value you anticipate testing.

(Top image) Use the resistance, or ohms, function to test switches. An "infinity" reading may indicate a defective switch.

(Bottom image) Touch probes to heating element leads. Compare the appliance specifications with the resistance readings in ohms on your multi meter.

Non-contact voltage testerVoltage "Sniffers"

Non-contact voltage testers detect the presence of AC voltage from 50 to 600 volts anywhere along an insulated wire. An audible signal and LED indicator alert the user.

Circuit analyzersOutlet Analyzers

Circuit analyzers are used to make sure receptacles are energized, grounded and polarized. Some also test GFCI receptacles and breakers and AFCI breakers.

Safety First -- Be Electrically Smart!

To ensure your safety when working with electricity, always take these basic precautions:

  • Turn off power to a circuit before working on it. Place a sign at the service panel to warn others.
  • Affix a piece of tape over breaker handle or fuse.
  • Wear safety glasses when working around electricity.
  • Never stand on a wet or damp floor when working with electricity. If necessary, cover the floor with rubber mats or dry boards.
  • After you've turned off a circuit breaker or pulled a fuse, use a voltage tester to check that the power actually is off.
  • Before touching any wire, use a voltage tester to make sure it isn't live.
  • When working on electrical wiring or appliances, avoid touching grounded metal pipes or fixtures.
  • Never replace a fuse with one of higher amperage.
  • Check your work with a voltage tester or outlet analyzer to make sure that it's properly wired and grounded.
  • Use rubber- or plastic-handled tools.
  • Never use aluminum or wet wood ladders near overhead wires.
  • Wear heavy rubber gloves if you are working on or in a service box.
  • Unplug appliances before working on them.
  • To protect small children, install safety covers in unused receptacles.
  • When unplugging a lamp or an appliance, pull the plug, not the cord.
  • Extension cords aren't a substitute for permanent wiring--put them away after each use. Don't run cords under rugs or where they may be stepped on or tripped over.

Last modified: Thursday, 2008-11-20 20:38 PST

Use the resistance, or ohms, function to test switches. An