November 2014
Beginner
288 pages
7h 52m
English
Content preview from Electrical Estimating Methods, 4th Edition
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CHAPTER 15 Starters, Boards, and Switches
Starters are electric controllers that accelerate a motor from rest to running speed; they are also used to stop the motor. Boards serve as a mounting for electric components and/or controls. Switches are devices used to open, close, or change the connection of an electric circuit. This chapter contains 18 sections and includes components ranging from panelboards and circuit breakers to motor control centers and meter sockets. Each of these components is defined, supplied with the appropriate units of measure, followed by material and labor requirements and the procedures involved in the takeoff.
CIRCUIT BREAKERS
Circuit breakers are used in general distribution and in branch circuits to protect the wires and equipment downstream from current overload. Circuit breakers are rated in amperes and are capable of interrupting their rated current at their rated voltage. There are several types of circuit breakers: magnetic trip only, molded case, current-limiting (which includes three coordinated current-limiting fuses), and electronic trip. An important parameter in selecting a breaker is its fault current interrupting capacity. Several different grades of breakers are available in most sizes, for different uses and conditions. The common ampere interruption capacity (AIC) ratings are 10,000 AIC; 22,000 AIC; 42,000 AIC; and 65,000 AIC. Their application is determined by the amount of energy available at the breaker's line side during a ...
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