Conduit Size

[JP Eiman]

We are running a 480 volt 400 amp 3-phase service using 3/0 copper in parallel. Is it ok to run all eight wires in one 4"conduit? If not does the size of the service make a difference or is never allowed? Thank you!

 

[iwire]

We are running a 480 volt 400 amp 3-phase service using 3/0 copper in parallel. Is it ok to run all eight wires in one 4"conduit?

Yes you can do that but you will have to derate the ampacity of the conductors as you will now have six, perhaps even eight current carrying conductors in one raceway.

 

[augie47]

I agree.
This is definitely a situation where the "devil is in the details".
IF you wish to place them all in one conduit you need to verify that your load will not exceed the adjusted ampacity, so the calculated load must be known.
Secondly you need to determine if your neutral is going to count as a current carrying conductor. If so, the 8 conductor deratiing will take you below the point a 400 amp main can be used.

 

[texie]

As Bob stated your derating will make the #3/0's too small even at 80%.
400*80%=320 amps next standard size 350 amps with a maximum load of 320.

Would not the math be (assuming 90* conductor): 225 X 2 = 450. 450 X 80% = 360?

If the OP's calculated load is less than 360 amp he could use a 400 OCPD.

 

[infinity]

Would not the math be (assuming 90* conductor): 225 X 2 = 450. 450 X 80% = 360?

If the OP's calculated load is less than 360 amp he could use a 400 OCPD.

Yes I posted before the first cup of coffee so removed it to avoid any more confusion.:ashamed1:

 

[JP Eiman]

Thanks to all, derating is not a problem but putting in a second conduit would be.

Thanks to all, derating is not a problem but putting in a second conduit would be.

Yes I posted before the first cup of coffee so removed it to avoid any more confusion.:ashamed1:

Many thanks, derating is not a problem but putting in a second conduit would be!

 

[texie]

Many thanks, derating is not a problem but putting in a second conduit would be!

FWIW, you could just use single 600 CU and get the full 400 amps. Or even a single 500 would get you closer. Come to think of it, you could use 2-4/0 and get the full 400. Your conduit will handle any of this.