Industrial control panel feeder

[jeff motta]

I am looking for some input, we are going to provide power for an industrial mixer, the nameplate rating is 38kw @ 208v 3 phase, it has two 15kw immersion heaters and 3 motors, 9a amps being the largest of the 3 the other two are 5 amps each, so far, I have come up with 131A, I would run 1/0 thhn for the feeder to the control cabinet but I feel like I have missed a step, I have not figured in the duty cycle of the heaters or motors yet, I am waiting on the client to provide info on how this mixer operates. Thanks for your time

 

[infinity]

Why wouldn't you just use the nameplate rating of 38kw?

 

[jeff motta]

Why wouldn't you just use the nameplate rating of 38kw?

I did use the nameplate rating to get the 131A, just wondering if there is anything else or if I missed something.

 

[infinity]

I did use the nameplate rating to get the 131A, just wondering if there is anything else or if I missed something.

How did you get 131 amps?

 

[MTW]

My calculation shows 38 KVA@208 = 105.48 A

 

[petersonra]

My calculation shows 38 KVA@208 = 105.48 A

105.48 x 1.25 = 131.

1/0 would certainly cover it but likely a bit of overkill.

IIRC, for a feeder is 125% of the largest motor plus 100% of everything else.

 

[petersonra]

30 kw = 84 Amps. Add 19 for the motors is 103.

Maybe a small transformer too.

 

[infinity]

This is piece of equipment with a nameplate rating. It is not a continuous load so why the 125%?

 

[petersonra]

This is piece of equipment with a nameplate rating. It is not a continuous load so why the 125%?

I think it is only 25% extra for the largest motor. I don't know why the OP used 125% of the whole thing. Not that it matters any. He can oversize the feeder if he wants to. I would have gone with 107 Amps minimum. But 1/0 will work fine as will a 150 amp cb for the feeder. Cost difference is probably not that much.

 

[jeff motta]

This is piece of equipment with a nameplate rating. It is not a continuous load so why the 125%?

When in use it will be continuous, they will run it for hours at a time.

 

[petersonra]

When in use it will be continuous, they will run it for hours at a time.

I don't think it matters if it is continuous or not for the purposes of determine the feeder ampacity.

By the way, it would be wise to look up the definition of continuous in NEC article 100.

 

[jeff motta]

I don't think it matters if it is continuous or not for the purposes of determine the feeder ampacity.

By the way, it would be wise to look up the definition of continuous in NEC article 100.

Bob, thanks I didn't look at it this way

 

[infinity]

Bob, thanks I didn't look at it this way

Yes the Article 100 definition of a continuous load is very specific. I cannot think of a scenario where this controller panel would be a continuous load.