30 HP Pump Motor Feed

[kwired]

It sounds like there will be other equipment located with the pump, so unless the pump room is actually part of the building with the supply panel, there will be multiple supply circuits going to what's probably a separate structure, and that a problem.

Is this pump and the supporting equipment part of the main building or part of a separate shed or pump room? That'll make all the difference.

I agree. One still could legally have what at first appears to be undersized conductors on said feeder all because of allowances for motor starting, but that likely means at least upsizing the conductor some for the additional loads even if the overcurrent device stays at 100.

 

[FountainGuy]

#8 conductors would be properly sized feeder conductors for the 100A feeder breaker, per 430.24 and 430.62.

David, I agree with you. I gave in to the EE and made the feed 80A, with a 100A disconnect switch, with #4 wire from the disconnect to the motor starter and motor protector, then #8 wire from the motor protector to the pump. I prefer a 100A feed, and its wasteful but ok to oversize the feed wire. Thanks for your help!

 

[FountainGuy]

It sounds like there will be other equipment located with the pump, so unless the pump room is actually part of the building with the supply panel, there will be multiple supply circuits going to what's probably a separate structure, and that a problem.

Is this pump and the supporting equipment part of the main building or part of a separate shed or pump room? That'll make all the difference.

Good questions. There are no other 480V loads on this feed but the 30HP pump. There is a separate 120/208V 3-phase feed for the rest of the equipment inside a pre-fabricated fiberglass underground pump vault. The pump vault (buried structure dedicated for the fountain) is located in a planter area about 75 feet from the fountain. [I tried to attach a catalog cut sheet of the pump vault in pdf format, but the file is 568KB in size.]

 

[Jraef]

#8 conductors would be properly sized feeder conductors for the 100A feeder breaker, per 430.24 and 430.62.

Yes, you're right, under 430.62 A) and assuming that is the only load.

Under 430.62 B), the breaker would have to be sized for the #8, or the conductors sized to 100A. Ergo my comment that the Engineer may have been wanting to err on the side of caution. If you size the conductors for the 100A rating of the breaker, what someone may do on that circuit in the future becomes irrelevant.

 

[david luchini]

Under 430.62 B), the breaker would have to be sized for the #8, or the conductors sized to 100A.

I don't think 430.62(B) says that. It doesn't seem to require anything, it is a permissive rule.

Edit: I cant' speak to the Engineer's motives, only what the Code requirements are. From post #11, it appears that the Engineer was suggesting that #8 feeder conductors from a 100A feeder breaker would be a violation.