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Cabel Capacity with Motor Starter?

Cabel Capacity with Motor Starter?

Cabel Capacity with Motor Starter?

(OP)
I'm having trouble figuring out which cable rating to use. I'm in a pump test facility and I'm needing to replace lead extensions that supply power to our test motors. My circuit breaker is 400 amp & 600 VAC max. However, the leads are fed through a motor starter which is rated 270 amps. In regards to NEC should all cable ratings be 400 amps? Or is it acceptable to have them rated for ~300 amps?

RE: Cabel Capacity with Motor Starter?

A test facility may be some kind of exception, but in general, the motor feeder must be sized at 125% of the motor FLA.  The breaker size is not a direct factor in the NEC way for motor feeders.  Article 430 covers sizing the breaker and feeder for a motor circuit. (This assumes only one motor running on this feeder.  If there are multiple motors, the sizing is a little different.)
 

RE: Cabel Capacity with Motor Starter?

(OP)
Ok, good deal. Yes, there is only one motor running of the feeder. Thanks a lot for your help! Merry Christmas!

RE: Cabel Capacity with Motor Starter?

It should be mentioned that the issue of the breaker size not being critical is ASSUMING you have a motor starter with it's own set of thermal overloads sqetmto protectmwhatever motor is being tested. It's usually a safe assumption but being a test facility, I have seen that not to be the case on occasion.  

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RE: Cabel Capacity with Motor Starter?

"However, the leads are fed through a motor starter which is rated 270 amps."
That's a little scary.  

Bill
--------------------
"Why not the best?"
Jimmy Carter

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