200 HP motor feed; paralleling verses larger single conductor

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thunder15j

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I am designing a feed to a 200 HP 480 volt motor that will power a water pump that will be running continuously, 3 hours or more. The motor will not be pulling full load.

NEC table 240.15 200 HP motor feed= 240 amps; cont duty. 1.25x = 300 amps. 350 mcm. $5.30 ft +/- cu

Paralleling 2/0 cu: 2/0 @ 90c = 195 amps; 4-6 conductors in raceway (310.15 B 2 a) .8 x 195=156 amps. 2 wires per phase @ 2 x156= 312 amps. $ 1.96/ft x 2 =3.92/ ft .

Substantial savings can be gained by paralleling the wire, especially one that might be several hundred feet long The method of motor control will be a soft-starter with bypass. I am always concerned about any heat transfer to the electronics of the controller especially with a soft starter. I do realize that voltage drop needs to be addressed and also labor costs. In this particular installation. neither is a factor.

My only real concern here is the fact that because I used the 90 degrees Celsius rating for the wire ampacity, is there a risk of any heat being conducted to the starter.

Any remarks on my design would be appreciated. Thank you
 
Nope because they were derated, besides the conductors are only going to see 240A, when divided by 2 is 120A each, so, the cable will never even reach 75deg C assuming 30deg C ambient.

Matter of fact they won't even reach 60deg C.
 
Motors are not subject to 125% continuous load factoring. However, for single motor feeders, you will have to size conductors to 125% in most cases. The ampacity will be the lower of the 75?C value of the conductor size used [110.14(C)] or value after the application of adjustment and correction factors [310.15(B)(3), typically] using 90?C table value.

Reduction in cost by paralleling in lieu of larger single conductors is a common practice.
 
Smart $ said:
Reduction in cost by paralleling in lieu of larger single conductors is a common practice.
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And with very large conductors where both skin effect and cooling via surface area become factors, the amount of copper required is significantly less. It is not just that the smaller conductors are easier to handle.
 
Many folks find an added positive factor in paralleling is the greater flexibility of the smaller conductors when wrestling them in the small size allowable motor peckerheads.
 
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