Circuit Breaker Basics

A circuit breaker has two primary functions:
1. to provide a nonautomatic means to energize and de-energize the circuit
2. to open automatically to protect the circuit from damage due to an overcurrent condition. In other words, a circuit breaker must be able to be switched on and off, and it must open automatically during an overcurrent condition. In order to open automatically, circuit breakers are equipped with some type of tripping mechanism. Some circuit breakers employ electro mechanical tripping mechanisms, some use hydromechanical tripping mechanisms, and some use electronic tripping mechanisms

Electronic trip circuit breakers from Square D Company use the MICROLOGIC® tripping
system, which includes current sensors, a microprocessor-based trip unit and a tripping solenoidElectronic trip molded case circuit breakers are designed to meet UL489, Underwriters Laboratories Standard for Safety for Molded-Case Circuit Breakers and Circuit Breaker Enclosures

In most cases, the basic overcurrent protection provided by standard thermal-magnetic circuit breakers will meet the requirements of the electrical system design. In some cases, however, basic overcurrent protection might not be enough.
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