A multimeter is a device used in diagnosing electrical problems. It can be used to test resistance and to measure voltage. Resistance can be safely tested with the power off. However, voltage can only be measured with the power on. Because of the risk of electric shock, an individual trained in the use of a voltage tester should only conduct voltage tests.
The tests described below should be done when current is NOT present. Always unplug the device or turn off the main circuit breaker before attempting these tests. Always test your test equipment for proper operation before use.
The common multimeter is a small handheld device with an indicator needle over a measurement scale or a numeric LCD display. The device has a switch to select the type of test to be performed. A multimeter also has two wires, one red (+) and one black (-), with metal tips. They are called probes.