Continuity refers to being part of a complete or connected whole. In electrical applications, when an electrical circuit is capable of conducting current, it demonstrates electrical continuity. It is also said to be “closed,” because the circuit is complete. In the case of a light switch, for example, the circuit is closed and capable of conducting electricity when the switch is flipped to "on." The user can break the continuity by flipping the switch to "off," opening the circuit and rendering it incapable of conducting electricity.
For consumers, the most obvious sign that there is an electrical continuity issue with their wiring is when plugged-in electrical devices fail to work. However, unintended breaks in continuity can have more serious consequences, such as electrical fires or damage to electrical equipment, and therefore, it is recommended that all electrical wiring be kept in good working order and properly maintained.
A number of devices are manufactured to assist consumers in testing electrical continuity, ranging from multimeters, which have a wide range of additional applications, to simple testers that light up if continuity is present. These devices use two electrical probes, which form a complete circuit when touched together. Consumers can test the device to ensure that it is working properly by turning it on and touching the probes together – the meter should read zero, or the indicator light should turn on, indicating a closed circuit. When the probes are not touching anything, the metered device will read infinity, showing that the circuit is open.
When testing a circuit for electrical continuity, consumers should first cut off power to the circuit by unplugging the device or turning off the main circuit breaker. Failure to do this may result in severe shock. To test for electrical continuity, turn on the testing device and place one probe at each pole or terminal of the circuit being tested. When testing a switch, for example, if the switch is in the "on" position, the reading should be close to zero, and when the switch is off, the reading should be infinity. A simpler continuity tester with an indicator light will be illuminated when the switch is on, and dark when it is not.