Hence, circuit breakers should be periodically tested to see whether they operate at the correct operating time specified by the manufacturer.Being mechanical devices, circuit breaker are made of numerous springs, washers, and linkages. These components can get jammed, the lubricating oil in the linkages can evaporate or lose its properties. The lubricating oil can mix with dust and form a viscous deposit. This can cause partial seizure and is particularly true for circuit breakers which are kept in the closed or open position for very long periods of time.
The Circuit Breaker operating time can be measured by special testing equipment known as the Time interval meters. These instruments measure the time between the signal to open and the actual interruption of the current. The opening time of the contacts belonging to each individual phase is measured.