matching breakers with wire size


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Old 07-29-09, 04:27 PM
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matching breakers with wire size

For sizing up breakers and wires. Is it correct that the ampacity of the conductor must be equal to or greater than the breaker it is fed from?
 
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Old 07-29-09, 04:36 PM
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With the occasional exception of welders and motors yes, Yes in some cases such as distances over 100 ft it may need to exceed the ampacity of the breaker.
 
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Old 07-29-09, 04:45 PM
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Of course the allowed over current device (fuse or breaker) will also depend on other things like; wire connection ratings, type of wire, how many wires in a conduit, small conductors, etc.
 
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Old 07-29-09, 06:29 PM
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Motor loads are a special chapter in the NEC. Very much abbreviated, the rules generally state that the conductors are sized to the full load running current of the motors and the circuit breakers may be sized to as high as 250% of the full load running current of the motor for single motor per circuit breaker loads. This can often mean that the conductor would be considerably smaller than would normally be used with a specific circuit breaker. You may need to upsize the conductors to allow for voltage drop.

These rules assume that the circuit breaker is for short circuit protection only and that the motors are protected from overload by a motor starter or integral thermal overload device.
 
 

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