Parallel Feeders For 800A Service/ (2) 400A Loads

[electriciansnet]

Hello everyone! Long time...
I have been asked to find the most efficient way to feed (2) 400A 42 circuit panels in this large but non-mainstream grocery store. From the utility xfrmr pad (approx 50' away) to the area where the new CT cabinet/ disconnect will be mounted on the back of the building I have (1) spare 4" PVC. From the back of the building (service) to the panels is approx. 250' where I already have between 2 & 4 spare 3" EMTs. What the architect has drawn is (2) 4" PVC w/ (4)#600 to (2) 300A disconnects and parallel(x2) 3/0 , #6G in 3" EMT to 400A panels.
I definitely want to utilize the 3" EMT and 4" PVC and I will either exclude the demo of the sidewalk and add another 4" PVC if I need to
(there's immediate plans for the remaining space which will require more 4" anyway) and I definitely cannot get feeders rated for 800A in one 4" but everyone involved feels like there must be a better way.
Such as, 800A disconnect...

Has anyone had a similar situation recently?

 

[electriciansnet]

correction: (2) 400A disconnects

correction: (2) 400A disconnects

correction: (2) 400A disconnects

 

[Crionics]

Hello everyone! Long time...
I have been asked to find the most efficient way to feed (2) 400A 42 circuit panels in this large but non-mainstream grocery store. From the utility xfrmr pad (approx 50' away) to the area where the new CT cabinet/ disconnect will be mounted on the back of the building I have (1) spare 4" PVC. From the back of the building (service) to the panels is approx. 250' where I already have between 2 & 4 spare 3" EMTs. What the architect has drawn is (2) 4" PVC w/ (4)#600 to (2) 300A disconnects and parallel(x2) 3/0 , #6G in 3" EMT to 400A panels.
I definitely want to utilize the 3" EMT and 4" PVC and I will either exclude the demo of the sidewalk and add another 4" PVC if I need to
(there's immediate plans for the remaining space which will require more 4" anyway) and I definitely cannot get feeders rated for 800A in one 4" but everyone involved feels like there must be a better way.
Such as, 800A disconnect...

Has anyone had a similar situation recently?

First question...why is an architect specifying conductor sizes. is there an engineer on the project? there are multiple problems I see if I understand you correctly.

 

[augie47]

Since the one 4" won't handle your service, you seem pretty well trapped into installing another service conduit.
If I understand, he is calling for parallel 3/0s in one conduit. Without seeing his load calculations, I don't fully understand the reasoning in the 600s in the service conduits with a 420 amp capacity and parallel 3/0s
on the load side with a ampacity of 360 amps (paralleled).
Also, the #6 would be undersized for a 400 amp feeder EG.

 

[Cow]

Correct me if I'm wrong, but as long as you have 2 or more service disconnects, you can size the wire for the load rather than the 800 amps. So if you set a CT can with two 400 amp disconnects, you might be able to shrink the service wire a little bit if you don't actually need 800 amps.

Looking at the conduit fill charts and ampacity tables, you can pull 7 -500's in a 4" pvc. That'd give you two 500's for every phase and one 500 for a neutral. With derating that's 688 amps worth of wire ampacity and 380 amps of available neutral load.

Obviously, the best bet would be to run another one or two 4" inchers and have a future spare.