600A Distribution Board

[jgdpsu]

Hi all, I have an interesting problem.

I'm working on an adding a new building at an existing plant. The plant has 600A service feeding a 600A ATS. Connected directly to the load side lugs of the ATS they have 2-600A feeders (2 sets of 350kcmil each) feeding 2-400A panelboards. The reason the feeders are a full 600A is b/c this is technically a tap w/o overcurrent protection b/c of the distance to the panelboards. Also on the load lugs of the ATS they have 2-100A feeders which feed adjacent enclosed circuit breakers (taps w/ overcurrent protection). So that's essentially 2-400A/3P feeders and 2-100A/2P feeders right on the load lugs of the ATS.

My predicament is that I need to add a third 400A/3P feeder. Is it legal to get a 600A, 120/208V, 3?, 4 wire distribution board with 3-400A/3P circuit breakers and 2-100A/2P circuit breakers? I have checked the current existing loads and each 400A existing panelboard only drawings about 100A each and the new 400A feed would have a typical load of 75 HP or 211A. So that totals to about 411A on the 600A service.

Thanks in advance for any help

 

[augie47]

panelboard

panelboard

If I understand your question correctly, yes it is legal.
In an enlarged sense , its no different from a 200 amp loadcenter with 400 amps worth of branch breakers.
From you original post, however, I do have a question. What serves as the service disconnect? Is the ATS service rated, or is there OCP ahead of it ?

 

[jgdpsu]

Thanks...your logic is what I was thinking as well and Square D has no problem making up the configuration I listed.

As for OCP...yes, there is a 600A MCB right before the ATS and the generator has it's own 600A CB (all in the same room within a few feet).