Trip mechanisms circuit-breaker

Instrument alarms and trips should be tested by simulation of trip conditions as far as possible during system commissioning. It is recommended in the case of trips that the function and mechanism in each case be verified by testing the system in its entirety. For example, in the case of a high-pressure rectifier trip, the system pressure should be raised to the trip value and all actions through to the circuit breaker should be observed. 

A circuit breaker, although more expensive than a fuse, has several advantages for excess current circuit protection. The principle of operation is that excess current flow is detected electromagnetically and the mechanism of the breaker automatically trips and cuts off electricity supply to the circuit it protects. Circuit breakers are also available to detect earth leakage current and, indeed, units are available that detect both over-current and earth leakage currents and thereby give very good circuit protection. 

Fuses and circuit breakers are over-current devices that are placed in circuits to monitor the amount of current that the circuit will carry. They automatically open or break the circuit when the amount of current flow becomes excessive and therefore unsafe. Fuses are designed to melt when too much current flows through them. Circuit breakers, on the other hand, are designed to trip open the circuit by electro-mechanical means. 

SPECIAL CAUTIONARY NOTE AU circuit breaker manufacturers recommend that their circuit breakers be exercised annuaUy via the trip test button. Exercising the circuit breaker actuates the trip mechanism. The trip mechanism of the circuit breaker is separate from the on-off handle mechanism, and annual operation of the trip mechanism ensures that the breaker wiU trip when called on to operate. This is also a test indication if the breaker faUs to trip, it has malfunctioned and should be replaced. 

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