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Circuit Breaker Certification

Manufacturers change protection methodologies found in low- voltage power, insulated-case, and molded-case circuit breakers constantly. Some of these changes are in response to new requirements such as NFPA 70, NFPA 70E, UL, and other standards. Other changes are simply improved methods to help a manufacturer garner a larger market share.

Before discussing testing and certification techniques for low-voltage circuit breakers (Part II of this story), here is an overview of some common types—and some misconceptions.

I2t/I4t Response Type

By default, digital electronic devices have an on/off nature. For example, in a low-voltage breaker trip unit, when a short-time set point is reached, the trip unit goes into pickup, and the timing circuit starts the countdown to the trip time based on the short-time delay setting. The result is a very discrete and square time-current curve across all protective functions.

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