Parallel Feeders In One Conduit

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_BlueCollar_

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My company recently subbed out a job due to scheduling conflicts. A small retail project, new construction, 20,000 sqf., Single Phase, 500A, 120/240 Overhead service with Main Disconnect and CT can on the exterior of the building, and Distribution Equipment back to back with the Main Disconnect but on the inside of the building. As a journeyman and the lead man on the 9 previous stores (this is a franchise), I was sent to do a walk through and some layout with our sub. I told him I wanted 2 x 2" IMC Risers, 3 x 250 CU in each into the CT can, 2 x 2" EMT Nipples from the CT Can into the Main Disconnect and 2 x 2" EMT Nipples from the Main Disconnect through the wall into the back of the Distribution Panel. The sub, who is a Licensed Master Electrician asked why he couldn't upsize the pipe to 3" and run everything in one piece of pipe. We had an argument and he asked me to show him where in the NEC it says parallel conductors must be ran in separate conduit runs, and I couldn't. I know I'm young and don't have as much experience as him, but I've never performed nor seen an installation where parallel feeders were ran in one piece of conduit. Can anyone tell me if it's just common practice to run multiple pieces of conduit for parallel conductors? Is it legal to put everything in one piece of conduit? Where in the NEC do I look?
 
You can run parallel conductors in single circular raceway. If the raceway exceeds 24" then derating must be applied.

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If I was doing that in parallel, it would be parallel 3/0s, not 250s. For a 400 amp service, there is no advantage in running two conduits, each with 250 kcmil over running a single conduit with 500kcmil.
As far as having both sets of 250s in a single conduit, even with derating, it would be code compliant, assuming that the calculated load is 464 amps or less.
 
_BlueCollar_ said:
My company recently subbed out a job due to scheduling conflicts. A small retail project, new construction, 20,000 sqf., Single Phase, 500A, 120/240 Overhead service with Main Disconnect and CT can on the exterior of the building, and Distribution Equipment back to back with the Main Disconnect but on the inside of the building. As a journeyman and the lead man on the 9 previous stores (this is a franchise), I was sent to do a walk through and some layout with our sub. I told him I wanted 2 x 2" IMC Risers, 3 x 250 CU in each into the CT can, 2 x 2" EMT Nipples from the CT Can into the Main Disconnect and 2 x 2" EMT Nipples from the Main Disconnect through the wall into the back of the Distribution Panel. The sub, who is a Licensed Master Electrician asked why he couldn't upsize the pipe to 3" and run everything in one piece of pipe. We had an argument and he asked me to show him where in the NEC it says parallel conductors must be ran in separate conduit runs, and I couldn't. I know I'm young and don't have as much experience as him, but I've never performed nor seen an installation where parallel feeders were ran in one piece of conduit. Can anyone tell me if it's just common practice to run multiple pieces of conduit for parallel conductors? Is it legal to put everything in one piece of conduit? Where in the NEC do I look?
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There is no requirement to run separate conduits for parallel sets, as long as you account for all applicable derate rules.

Generally, you'll need 1 larger size of wire than you would for 2 individual parallel sets, if you choose to use a common conduit.

Parallel 250's = 510 A in separate conduits, or 464 A in the same conduit.
Parallel 300's = 570 A in separate conduits, or 512 A in the same conduit.

Another reason you might use separate conduits is pulling logistics. Generally, aughts are easy to parallel in the same pipe, and high kcmil are difficult.
 
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