How To Conduct a Multimeter Continuity Test

A multimeter is a useful measuring device. It’s a voltmeter, ammeter and ohmmeter all in one (hence the name), and it comes with auxiliary functions as well.

My multimeter features a setting that lets me test whether a diode is good. That’s handy when trying to find which of the LEDs in a string of Christmas lights has failed, causing the entire string to go out.

Another common household use: Checking for voltage while doing electrical repairs. When you’re replacing a receptacle and you’re not sure if you turned off the right breaker, a multimeter makes sure the voltage in the wires is zero.

It can also measure electrical resistance, which determines if electricity flows unimpeded through a device or a wire (continuity) or can’t flow at all (no continuity). Many multimeters offer a continuity setting on the dial that produces an audible beep when the meter detects continuity.

What Is a Multimeter?

A multimeter is a pocket-size testing device that measures voltage in volts (V), current in amps (A) and resistance in ohms (Ω) in an electrical circuit.

Modern multimeters are portable versions of the amps/volts/ohms (AVO) meter invented in 1920 by British postal engineer Donald Macadie. Besides streamlining Macadie’s original design, modern manufacturers included extra functionality — things like testing diodes and capacitors, and automatically adjusting measuring sensitivity.

On the front of the device, you’ll see an LED display that lets you select the parameter you want to measure and, on older models, a sensitivity range for each parameter. You’ll see three or four ports for the test leads, one labeled common (COM), one for voltage/resistance (V/Ω) and one for current (A). Sometimes there’s also one for milli- and micro-amps (mA/µA).

The ports you need for a continuity test are COM and V/Ω. And because the test involves sending a small current through the circuit, the device has an AA battery.

What Is Continuity?

When you test for continuity, you’re determining whether electricity can pass unhindered through a lamp cord, extension cord, switch, receptacle or some other electrical device.

The multimeter generates a small electric current. If there is continuity, the multimeter will show zero resistance. If it has this capability, you’ll hear a beep. But if there’s a break in the circuit or device, the meter will show infinite or high resistance and remain silent.

How To Conduct a Continuity Test

Materials required

• Multimeter;
• Two test probes (usually supplied with the multimeter);
• Screwdriver (for disconnecting device terminals).

Isolate the device you’re testing

To conduct a successful test, no residual electrical current can interfere with the signal generated by the multimeter. In most cases, this means disconnecting the switch, fuse or device you’re testing from any source of power.

If testing a wall switch, don’t turning off the breaker, because electricity can “leak” in from other live circuits. After turning off the breaker, disconnect the wires from the switch. If you’re checking components of an electrical appliance, unplugging it usually does the trick.

Set up and test the multimeter

Plug the black probe into the COM port and plug the red probe into the V/Ω port. If your multimeter has the setting, set the dial to measure continuity. Otherwise, set the multimeter to measure Ω (resistance).

Turn it on and test it by touching the probes together. Because they form a complete circuit, the multimeter should beep and read zero ohms of resistance.

How To Test a Wall Switch for Continuity

A switch has two brass terminal screws and a ground screw. To test the switch, turn it on and touch one of the multimeter probes to one terminal screw (it doesn’t matter which one) and the other probe to the other terminal. If the switch is good, you should hear a beep and the multimeter should display zero.

Now turn the switch off and repeat the test. If the switch is good, the multimeter won’t beep but will display infinite resistance. Some models display Open or a similar message.

How To Test a Fuse for Continuity

A fuse features input and output terminals. The fuse is designed to “blow” (stop current from flowing) when the input current exceeds a preset threshold. A continuity test can tell you whether a fuse has blown and needs to be replaced.

With the fuse terminals disconnected, touch one probe to one terminal and the other probe to the other terminal. If the fuse is good, you’ll hear a beep, and the multimeter will show zero resistance. If the fuse has blown, you’ll hear nothing and the multimeter will show infinite resistance (or Open).

How To Test a Wire for Continuity

Did you run over your extension cord with the lawnmower? Wondering if it’s still good? Here’s how to check.

Touch one of the multimeter leads to a male prong and insert the other probe into the corresponding female receptacle. If you get a zero reading, the wire is unbroken.

After checking the other wire, cross-check by touching the probe to one of the male prongs and inserting the other probe into the opposite receptacle. You should get no continuity. If you do, it means something sliced through the insulation and the wires are touching each other.

You can also test a lamp wire by touching one probe to one of the male prongs on the cord, the other probe to the light socket, then turning the switch on and off. You should get continuity with the switch on, and no continuity with the switch off.