compressor feeder size

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Toros

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Tujunga, CA
Hi,
I have to hook up a blow mold compressor in the existing manufactory;
Here is my engineering/calculation, Does this make sense???

Compressor name plate reading: @460v , 150 HP , RPM of 750 by "Petstar-550"
Per NEC:430-250, 150HP @ 460v has 180 FLA

therefore requires 300A , 3pole disconnecting means w/(3) 225A fuses (180 FLA x 125%=225A), and
This much power would be delivered through a feeder composed of (3) 4/0 thhn, cu @ 75deg. , per NEC:310-15(B16).

Thank you for your feedback/input
 
We have a lack of information to provide a short answer.
(a) Is this a "package" pre-wired compressor with motor, controller, etc.
If so, my first step would be to look for namplate or manufacturer input.
(b) Is the motor controlled by a drive of some type {not part of a package (a) } ?
If so, look for mfg or drive info and refer to 430 Part X
(c) Is the motor across the line start ?


With that size motor, (a),or (b) is much more common and in many case the manufacturer has info to consider.

In any event, you fusible switch would need to be HP rated also (430.109).
Unless you are using the switch for overload protection, fuses set at 125% of FLA might open and cause single phasing, especially on a compressor, IMO. In all probability there is some other means of overload present and you are providing short-circuit GF protection. If so, refer to 430.52. Your fuses are more likely to be in the 300 amp range.

Without taking into account any adjustment factors or voltage-drop, your 4/0 conductors would be minimum size..
 
Edwardtomas said:
...
Compressor name plate reading: @460v , 150 HP , RPM of 750 by "Petstar-550"
Per NEC:430-250, 150HP @ 460v has 180 FLA ...
Click to expand...
Per 430.6(A)(1) you have to use the motor nameplate full load current and not the current from Table 430.250 for this motor.
 
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