What Is a Molded Case Circuit Breaker?

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If your home has been constructed or remolded in the past 25 years, you're probably familiar with the molded case circuit breaker. These all-in-one components sit neatly inside the main electrical panel of your home and business and perform their service quietly, only to make themselves known when they have performed the task of over-current protection.

History

  • Replacing glass and long cylindrical fuses, molded case circuit breakers have brought cost savings and reliability with their introduction. At one point in time, if a fuse blew, they would have to be replaced in order for the electrical power to be reinstated to a particular circuit. Many times though, the fuse may blow again as the problem may have not been corrected. A molded case circuit breaker, on the other hand, does not have the problem of a one-time usage.

Significance

  • Resetting a circuit breaker is much like turning on a light switch. A simple flip and the over-current protection device can be reset and reused hundreds of times. This type of reliability has saved homeowners countless dollars and time from not having to replace a blown fuse.

Function

  • Molded case circuit breakers are manufactured in such a way so the end user will not have access to the internal workings of the over-current protection device. Generally constructed of two pieces of heavy-duty electrically insulated plastic, these two halves are riveted together to form the whole. Inside the plastic shell is a series of thermal elements and a spring-loaded trigger. When the thermal element gets too warm, from an over-current situation, the spring trips, which in turn will shut off the electrical circuit.

Types

  • Large industrial molded case circuit breakers can also have an adjustable range setting included on the face of the device. Generally used for higher amperages, 100 amperes or greater, these main circuit breakers can be adjusted for spikes that may occur in starting certain equipment.

Size

  • Molded circuit breakers can range in size from 15 amperes for the home and up to 3000 amperes for industrial settings and equipment. The larger industrial breakers can also be enclosed in metal cabinets twice the size of a common household refrigerator.

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References

  • National Electrical Code; NFPA; 1988
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