400 amp service advice?

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journeyman0217

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philadelphia,pa
I have to run a 400amp three phase service to a warehouse from a pad mounted transformer that is approximately 75' away. Looking for advice on how to run the wires and what wire. Is it better or easier to run 500mcm copper or parallel al 250's. I figured I would run 4" pvc for the 500's or 2 3" pvc for the 250's. This is my first 400amp service I'm doing on my own, so any advice would be appreciated.
Thx
 
I would do a cost analysis of the job and see what is less expensive. It is very hard to keep the wires the same length when doing parallel runs so I might prefer the single run.

I just noticed you have copper for the 500 kcm. It may be cheaper to go with the parallel 250.. You can actually get by with parallel 4/0 aluminum in a 2" conduit if the calculated load is less than 360 amps.
 
Dennis Alwon said:
I would do a cost analysis of the job and see what is less expensive. It is very hard to keep the wires the same length when doing parallel runs so I might prefer the single run.

I just noticed you have copper for the 500 kcm. It may be cheaper to go with the parallel 250.. You can actually get by with parallel 4/0 aluminum in a 2" conduit if the calculated load is less than 360 amps.
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what code article can I find that? I used article 240.4 b to size the 500 kcmil for a 400 amp service, that article would not apply to parallel conductors correct? for instance bumping 4/0 al from 180 to 205?
 
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journeyman0217 said:
so you can up size the breaker for parallel conductors? i don't see anything about calculated load?
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It doesn't but article 310 states that 4/0 is only good for 180 amps so in parallel we have 360 amps. This section will not allow 4/0 in parallel to be used over 360 amps
 
Dennis Alwon said:
It doesn't but article 310 states that 4/0 is only good for 180 amps so in parallel we have 360 amps. This section will not allow 4/0 in parallel to be used over 360 amps
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And to add to what Dennis said here - you can load parallel 4/0 up to 360 amps and still protect it with a 400 amp overcurrent device. But if you had 361 amps of load you would have to increase the conductor size even if still protecting it with 400 amp device.

Once you get over 800 amps - you can no longer "round up" overcurrent protection device on a conductor.

Same rule applies to your 500 copper option. 500 copper is only good for 380 amps - you can protect it with 400 amps provided the actual load doesn't exceed 380. You can parallel two 500's for an 800 amp overcurrent device - but actual load can't exceed 760. But you can not protect 3 parallel 500's with a 1200 amp device because you can no longer use the next size once you go over 800 amps.

This is found in the already mentioned 240.4(B).
 
Once you get past the fact that 500 copper will cost more then 4/0 or even 250 aluminum for material alone - then consider how much labor and other handling costs will be in comparison. 250 aluminum is hard labor to pull but can likely be hand pulled in your application, 500 copper likely will need additional equipment to assist with pulling.

2- 2 inch raceways is also going to cost less then a 4 inch raceway, won't be a terrible difference labor wise for PVC raceways, but should you be running RMC, I don't even want to think about man handling a 10' piece of 4 inch alone.
 
I see...you can round up to the next breaker size as long as you don't exceed the conductor ampacity... I would like the full rating of 400 amps so it seems like I should probably run the al 250's rather than 600 copper then. Thanks for the advice guys!
 
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