Back To Basics

The testing required and the standards that must be met by a low voltage power circuit breaker depend on the area of the world where the circuit breaker is applied. To play a major international role, low voltage power circuit breakers should be able to meet the requirements of ANSI, UL and IEC (Figure 34).

Figure 34. Dominant Worldwide Standards

As you continue through this module, you will become well aware that the required testing is the key factor in defining the type of circuit breaker. In a very general and simplistic way, low voltage power circuit breakers undergo a sequence of four rigorous tests.

Molded case circuit breakers, for example, are subjected to tests similar to numbers 1, 2 and 3. The fourth test sequence, momentary rating test , is specific to power circuit breakers and to some IEC molded case circuit breakers.

Specific testing details will not be covered in this module. It should be pointed out, however, that the momentary rating test just mentioned (test sequence 4) subjects the circuit breaker to tremendous physical forces and severe heating effects. Very simply speaking, the circuit breaker is subjected to its full short time current rating for two (2) time periods up to 30 cycles each. The short time rating indicates what magnitude of current the circuit breaker can stand with its contacts closed for a short period without being damaged. The circuit breaker’s short time rating is often equal to its 600 volt interrupting capacity. A low voltage power circuit breaker must be strong enough to survive this test and function properly after completion.