Arc Fault Circuit Interrupter

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This article is intended to supplement your knowledge beyond the immediate requirements of the NEC. It covers the types of circuit breakers that are found in various types of facilities today. The beginning lays a foundation (a review for many) and progress to introducing molded case, Insulated case, and drawout types with the series ending with the most advanced of all, microprocessor based circuit protective devices that are becoming more common. The following topics are covered in this the
first part of the article:
? Circuit Breakers Defined
? Circuit Breakers As Switches
? Current Levels To Be Broken
? Over-Currents
? Current and Temperature
? Circuit Breakers As High Temperature Limit Switches
? Ampacities Of Electrical Conductors
? Short Circuits
? Shorts To Ground
? Arcing Faults
? Bolted Faults
? Safety First, Always First
? NEC requirements For Circuit Breakers

Let us begin by defining circuit breakers then we will delve into some of the "nice to know" details about the relationships of current, temperature, and ampacities of conductors. The subject of faults and the various types of faults will then be covered.
The topic of safety while next to last is highlighted as being of first order importance. The final topic for this part is a brief listing of some of the general NEC requirements relating to circuit breakers.

The American National Standards Institute (ANSI) defines a circuit breaker as: ?A mechanical switching device, capable of making, carrying and breaking currents under normal circuit conditions. Also capable of making and carrying for a specified time and breaking currents under specified abnormal circuit conditions, such as those of a short circuit.? The NEC defines a circuit breaker as ? a device designed to open and close a circuit by non designed to open and close a circuit by non----automatic means, and to open the automatic means, and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within it?s rating.? While the ANSI and the NEC definitions describe the same family of devices, they do have some differences. The same is true with the actual circuit breakers themselves. They are much the same in general terms; however, there are a number of significant differences between the many types of electrical circuit breakers installed in various types of facilities today.

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