How to Test for Electrical Continuity
In the course of making electrical repairs, professional electricians and serious DIYers may need to test wall switches, light fixtures, lamps, or other devices to see whether their internal electrical pathways are intact, or continuous. This simple diagnostic test can help pinpoint the cause of an electrical problem. For example, if a ceiling light doesn't work, detaching both the fixture and wall switch and testing each for continuity can determine which device needs replacement.
Among the various diagnostic tools that electricians and serious DIYers use in the course of electrical repairs are two that are often used to test devices and wiring for continuity: the continuity tester and the multimeter.
What Is a Continuity Tester?
A continuity tester is a small battery-operated device with two electrical leads and an internal light bulb or LED. It is used for one job only: testing switches and other devices to see whether or not their internal electrical pathways are intact. When the wire leads are connected to both ends of an electrical pathway and the tester is turned on, the small electrical charge provided by the battery will flow through the pathway and cause the tester's lightbulb to glow if the device's electrical pathway is intact. Failure to light up means the electrical pathway is faulty or interrupted.
What Is a Multimeter?
A multimeter is a battery-operated electrician's tool that has several functions: testing wiring for voltage, for amperage, or for resistance. It is through the resistance function that a multimeter can test a switch, light fixture, or another device for electrical continuity. Measured in ohms, resistance is a measure of opposition (resistance) to the free flow of current through wires or another metal pathway. A perfect metal pathway will have 0 ohms of resistance, while a broken pathway will show very high or infinite resistance.
Continuity Tester Basics
A continuity tester is a device that is powered by batteries. It has a pointed metal probe on one end and a wire lead with either an alligator clip or a probe at the other end. It is used to test the continuity of metal pathways, and you can see how it operates by simply touching the metal probe and the wire lead together. When doing this, you complete a circuit pathway, and a light or buzzer will go off to indicate there is a complete, continuous pathway. Any electrical pathway in a circuit, appliance, or device can be tested in a similar fashion.
These testers are great for checking to see if a device such as a single-pole switch is working properly, or to check lamp wiring to see if the electrical pathway is intact.
Professional electricians can use a continuity tester in several ways. In skilled hands, for example, the continuity tester can even determine if a short circuit exists: If two wires within a sheathed cable have melted together, the continuity tester will light up if you touch one probe to the black wire and the other to the white wire.
For most DIYers, though, the tool is most often used simply to test switches and other devices for continuity.
Unlike a neon circuit tester, which has a similar look, a continuity tester is not designed to be used on live wires. When checking a device for continuity, it is best to do this with the device disconnected from the circuit wires entirely. If you do use a continuity tester when the device is still connected to the circuit, it is essential that the circuit's power is turned off.
A multimeter is a sophisticated diagnostic tool that can test for several different electrical issues. You can test a system for either AC or DC voltage, amperage, open-circuit, or short-circuit problems, and you can also test to make sure the circuit pathways are intact and continuous—known as a continuity test. In this mode, the tool can therefore provide the same function as a continuity tester.
A multimeter is a battery-powered tool with two wire leads—one red, one black—that plug into sockets on the tool. The opposite ends of the leads are fitted with metal probes. On the face of the multimeter, a dial or digital setting allows you to set the tool to the type of test you wish to conduct.
Testing continuity with a multimeter is done by using the ohm setting on the tool, which measures the resistance of an electrical pathway. In essence, the less resistance in a pathway the greater the continuity. For example, if you touch the two wire leads on the multimeter together, it should read 0, or no resistance (perfect continuity). If the tool shows infinite resistance, on the other hand, it indicates there is no pathway whatsoever. Used this way, the tool can tell you if the current pathway through a device is complete or if it is opened and is no longer usable.
What You'll Need
Equipment / Tools
- Continuity tester or multimeter
How to Use a Continuity Tester on a Wall Switch
How you use a continuity tester will depend on the device being tested, but the general principle is always the same. A small electrical current is sent through the device's pathway to determine if it is intact (0 resistance) or is broken (infinite resistance). One of the easiest ways to understand and practice using a continuity tester is to use it on a simple single-pole wall switch.
Detach the Device from the Circuit
Turn off the circuit breaker controlling the circuit, then detach the wall switch from the circuit. (If you are testing a different device, it, too, is best to disconnect it from the circuit for testing.)
Activate the Continuity Tester
With a battery inserted in the continuity tester, turn on the tool and touch one probe (usually a fixed probe at the tip of the tool) to the other lead (usually an alligator clip attached to a long insulated wire lead). If the tool is operating properly, you will see its internal lightbulb or LED light up, indicating it is sensing a complete electrical pathway. If the tester does not light up with this test, it means that the tool is faulty, or perhaps needs a fresh battery.
Touch the Tester's Probes to the Device
Touch the two leads on the continuity tester to opposite ends of a device's electrical pathway. In the case of a single-pole wall switch, you will touch one lead to each of the brass screw terminals on the side of the switch.
Flip the Switch Lever
Toggle the switch's lever from the ON to the OFF position while the tester leads are touching the screw terminals. In a functional switch, the tester's light bulb will glow when the switch's lever is in the ON position but will go dark with the switch lever OFF. If this isn't the case, then you have identified a bad switch that must be replaced.
(Similarly, testing a lamp or other appliance may require you to flip its switch from the ON to the OFF position.)
How to Test for Continuity With a Multimeter
Disconnect the Device
Remove the device being tested from the circuit. This can involve shutting off the circuit and detaching it from the circuit wires, or unplugging an appliance from an outlet.
Set the Multimeter's Function
To test for continuity, turn the dial or set the digital controls on the tester to the ohm setting.
In this mode, you also have the ability to set a multiplier factor, which can be slightly confusing if you are unfamiliar with the tool. Since the testers are designed to test for a wide range of resistance on sophisticated electronic parts, it has multiplier ohm settings, indicated by markings such as X1, X10, XK1, etc., controlled by a dial or buttons. These multipliers tell you that the reading on the ohm meter should be multiplied by the number indicated on the dial. For example, if your dial is set for X10 and the meter reads 50 ohms, the actual resistance number is 10 x 50, or 500 ohms.
But for simple continuity tests of switches and other devices, the multiplier settings are not important. No matter how the tool's multiplier dial is set, you will be looking for a reading of 0 ohms to indicate perfect continuity in the switch or whatever device you are testing. Some meters have an audible alarm that indicates perfect continuity (0 ohms resistance).
Test for Continuity
Touch one probe of the tester to one end of the device's pathway, and touch the other probe to the other side. In the example of a single-pole wall switch, you will be touching the probes to the two screw terminals on the side of the switch. With the switch's toggle lever in the ON position, the multi-tester should read 0 if the metal pathway in the switch is intact.
Flip the switch's toggle back and forth to make sure the internal pathway opens and closes correctly—the multimeter should show 0 ohms when the switch is ON, infinity when the switch is OFF.
Testing Other Devices for Continuity
Now that you know the basics of how a continuity tester and multimeter work, you can use these same principles with other electrical devices. It's simply a matter of identifying both ends of the device's electrical pathway and touching the tester or multimeter's probes to those spots.
Here are some of the common applications for continuity testing:
- Testing lamp wiring (touch one probe to one of the plug-in prongs, the other to the metal lightbulb socket; flip lamp switch on and off).
- Testing light fixture wiring (touch one probe to fixture's ground screw, and the other to the metal light bulb socket).
- Testing lightbulb socket (touch one probe to the metal outer rim, the other to the contact point in the base of the socket).
- Testing appliance or extension cords (with cord detached, test each of the internal wires, from plug-in prong to opposite end).
- Testing fuses (touch one probe to each end of the fuse).
- Testing lightbulbs (touch one probe to outer threads, the other to the center of the base).