Checking continuity is a common application of the ohmmeter. Although stand-alone ohmmeters are available, an ohmmeter reading is commonly attained by using one of the functions on a digital multimeter or analogue volt-ohm-millimetre. The continuity check is performed to verify the presence or absence of a complete path for electric current through a wire or some electrical load. The continuity check is one of the most useful tests that a technician can perform when troubleshooting a malfunctioning electrical circuit.
Connect the test leads to the multimeter by plugging the red plug into the red jack and the black plug into the blackjack on the face of the meter.
Set the function switch to the "Ohms" function. If you digital meter is an "Auto-ranging" meter, the meter will select the proper ohms range to use. If you have a manual-ranging meter, you will have to select an ohms range appropriate to the circuit being tested. To check the continuity of a wire or the continuity of most home appliances, the R X 100 range is the range of choice.
Disconnect all power to the circuit being tested. Most modern digital meters have built-in protection against being destroyed by the application of voltage, but if the voltage exceeds what the meter is protected for, the voltage will destroy the meter. The ohmmeter has an internal battery that supplies all of the voltage necessary to check a wire or device for continuity.
Disconnect one end of the wire or one side of the load under test from the rest of the circuit. This is required to make an accurate continuity test. Unless the wire or component being tested is isolated from the rest of the circuit, the meter may indicate continuity when the component under test is defective because the meter will read a complete circuit through the other components in the circuit.
Place one of the test probes on the end of the wire that you disconnected, and move the second probe away from that point one component at a time. When the bad component is between the two test probes, an "O.L." will be displayed on the meter's liquid crystal display, indicating an open circuit. An open circuit means that continuity has been lost.
Things you need
- Digital multimeter
- Schematic for the circuit being serviced.