Feeder for multiple motors

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LRB

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Interior Alaska
I am installing a commercial air compressor and drier system. My service is 800A, 4 wire, 240 V high leg delta.

The compressor skid has 2-7 1/2 H P 3 phase belt driven compressors at 22 FLA and 25 FLA (the 25 A motor is 3 wire motor labeled for 200 V) and the drier is labeled 5.6 A, 230 V, 3 phase . I have an unloaded 3 phase 200 A C-H plug-in panel with-in 10 fT of compressor skid. Panel takes type CH breakers. Starters are prewired to motors.

Using one Feeder Breaker per 230.62 (NEC 2014) :

1 st 7 1/2 largest FLA = 50 A
2 nd 7 1/2 FLA = 22A
Drier = 6 A

Feeder Breaker size = 80 A

Am I correct so far? I will protect the drier with 15 A time delay fuses or panel mount 15 A breaker.

My feeder conductor will be:
125 % largest motor = 31.25
second motor = 22
Drier = 6

Total load =59.25 =# 4 AWG xhhw (75 C, CU, XHHW, 100 deg ambient temp)

Agree? If not why.

First time in 50 yrs I have figured 1 feeder breaker for multiple motors. Would normally have MCC bucket for each motor with MCP and starter combination or the Manufacture would have skid disconnects, starters and control pre wired and we would supply feeder breaker and conductor per engineered specks.

Again please confirm or give me directions for corrections.

LRB
 
Your calculations will work however, I would have concern with the 200 volt nameplate motor on 240 volts.
 
It might be worth your while to compare cost on a buck-boost transformer in lieu of replacing the motor.
 
Cow said:
I agree, keep it simple without adding unnecessary components. It's just one more thing that can fail.

How are you handling individual OCP for each motor?
Click to expand...
OCP .. just another component to fail :) (joking)
 
Update:
Met with owners this PM, and have decided on individual breakers for OCP. (my preference) Interesting note on voltages:
A-N 126
B-N 225
C-N 126
A-B 250
B-C 264
A-C 252

I knew the POCO was on the hot side, but any reason for the abnormally high, high leg. That is 1.79 * low leg, instead of 1.73. Other thing all phase to phase should be with in a couple volts, A-C is 12 V high???

This is on grain farm and there are ~ 30 motors on farm. They have not had any abnormal problems.

LRB
 
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