conduit sizing

[chad lawson]

I need to pull three seperate runs of three 600kcmil one 350 kcmil and a 1ought through two hundred fifty feet of metalic conduit with two ninety degrees. This service will be feeding a square d buss system and the service has been sized to allow for 100% continous duty. I know the code book has charts for wire fill but i am not familar with the derating calculations to allow for heat. Any help would be greatly appreciated.

 

[benaround]

You need 3 runs of conduit ?

 

[augie47]

I used a "calculator" and had to guesstimate a few things..
but your post leaves a few questions in my mind...
(a) what type insulation.. I used THHN
(b) if it's truly a "service" what is the 1/0 ? services normally don't have grounding conductors
(c) if it's a feeder, the 1/0 would be undersized for a OCP to match the 600's
(d) you mention heat.. how much heat.. what is the ambient ?
You provided the wire size so any heat should have already been taken into account determining the size
(e) what type metallic conduit


Using the sizes you gave the calculator comes up with 3" EMT, 3-1/2 Rigid

For a more accurate answer we need more info...

 

[chad lawson]

yes there will be three runs of conduit. and we are using thhn. and it is a branch feeder circiut to a new building. Maybe i should back up and give a little more information. I need to feed a 800amp 480v three phase with nuetral to a building with a pull of 250 feet from the switch gear. We hired a contractor to do the job and he sized all the wire and then speced 3" emt. Once we got the material in he skipped country. My guys installed the buss and conduit and when we went to pull it we actually blew the conduit apart and broke many ropes. My concern is that if the pipe was under sized did we damage the wire. Is there room in the conduit to account for heat. Our plant operates between 60-100 degrees farenhiet. I also spoke with another contractor that told me the 2008 NEC does not allow half sized nuetral conductors he could not quote the article though. I thought the wire might have also been oversized for what we needed. I do want 800amps 100% continous duty in that building. thanks for any help. I worked as a electrician many years ago for about seven years and am now the plants cnc electronic technician so i deal with plc's and drives not this anymore but we were left hanging so i had to get involved.

 

[infinity]

So this is what I'm seeing:

3-600 kmil, 1-350 kcmil, 1-#1/0 in a 3" EMT
250' long w/ 2-90 degree bends.

The conduit is tight but as Augie calculated it might work. What kind of rope/puller are you using?

 

[augie47]

double checked with calculator...as Rob says its' tight.. plenty of lube would be helpful
again 3" is good for EMT, and no much else..If you have any rigid, Sch 80 etc, no go.
Your Numbers are good.for 800 amps...actually oversized for ambient and voltage drop.
You can reduce the neutral to meet the load provided you don't go below 1/0 (due to paralleling and due to 215.2)

 

[Dennis Alwon]

Here's what I see. I see that 3 runs of 500kcm alum. conductors are good enough for 800 amps. Since you have decided to use 600KCM for whatever reason you now must increase the size of your EGC to 2/0 (art. 250.122(B)). The fact that you are using emt means that you don't need an EGC but if you choose to use it then it must be 4/0 alum. Now I haven't calculated the fill but it appears that you may be in trouble.

If these are copper conductors then you may need 2/0 copper EGC

 

[infinity]

Here's what I see. I see that 3 runs of 500kcm alum. conductors are good enough for 800 amps. Since you have decided to use 600KCM for whatever reason you now must increase the size of your EGC to 2/0 (art. 250.122(B)). The fact that you are using emt means that you don't need an EGC but if you choose to use it then it must be 4/0 alum. Now I haven't calculated the fill but it appears that you may be in trouble.

If these are copper conductors then you may need 2/0 copper EGC

He did say that he needs 800 amps continuous so that might impact his ampacity/EGC calculation. Since this pull is already hard I would eliminate the wire type EGC altogether.