Breaker sizing for an engineered motor systems

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cfitka

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We have an engineered plant vacuum system we bought that already has o/l protection and 60A fuses for overcurrent protection. All I am doing is writing a procedure for the installation. This system has a 30 hp, 460V, 1773 RPM, 36.5 FLA, 40 Deg C, Des B, 1.15 SF 3Ph Motor on it. What size of circuit breaker and what type will I be required to use?
 
cfitka said:
We have an engineered plant vacuum system we bought that already has o/l protection and 60A fuses for overcurrent protection. All I am doing is writing a procedure for the installation. This system has a 30 hp, 460V, 1773 RPM, 36.5 FLA, 40 Deg C, Des B, 1.15 SF 3Ph Motor on it. What size of circuit breaker and what type will I be required to use?
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Is the only load the motor load? If so, this would appear to be a motor feeder and thus would be sized according to the motor OCPD sizing criteria.

the type of breaker will be of a type compatible with the panel board it is located in.
 
It is the only motor and the 480 distribution panel is of Inverse Time Delay type. Am I still required to size the breaker to NEC OCPD criteria even though the system has OCP of fuses in the dsw? If so..I went by the sizing of 250% of the FLA of this particular motor which brought me to 91A and rounded up to a 100A breaker..does that sound right? Thanks.
 
cfitka said:
It is the only motor and the 480 distribution panel is of Inverse Time Delay type. Am I still required to size the breaker to NEC OCPD criteria even though the system has OCP of fuses in the dsw? If so..I went by the sizing of 250% of the FLA of this particular motor which brought me to 91A and rounded up to a 100A breaker..does that sound right? Thanks.
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You can make the feeder just about any size you want as long as the conductors have enough ampacity and they are properly protected.

There are design issues involved such as not making the wire larger than necessary for economic reasons. You also would want to make the rating of the OCPD large enough that it is unlikely to trip before the local fuses blow. There may also be an issue of wanting some spare capacity in the area to tap off of at a later date.

In any case this is a motor feeder and you should use the motor feeder sizing rules.
 
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