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#42094 - 09/15/04 06:22 PM 400 amp service
Merlin Offline

Registered: 01/27/04
Posts: 170
Loc: NW Indiana
I am feeding three 200 amp mains from a 400 amp meter. These will be feed from the meter via a 6"x6"x48" raceway immediately next to the meter. Each one will have it's own run of copper THHN from the meter. Will 3/0 THHN copper be sufficient considering the "fill" of the raceway. Also does the nuetral need to be 3/0 or can I go smaller.

Also, this service load will travel from each main, underground a distance of 10 feet. Then up a pole in sch 40 pvc to seperate laterals feeding several different load centers. (this is on a farm to feed grain dryers and a shop) If I were to use 3" pvc up the pole and 3 seperate runs of 4/0 URD, (one from each main) Can they all be in one 3" conduit?

This is any existing service upgrade, so this is what I have to work with. The reason for using 3 mains is; 1) to be able to isolate areas for repair without affecting others, and 2) due to the cost difference of a 400 amp 3R main breaker enclosure. $400 vs $2000

Thanks for the help

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#42095 - 09/16/04 10:42 PM Re: 400 amp service
CJS Offline

Registered: 09/16/04
Posts: 35
Loc: Sanford,NC, USA
You will have to go to the book and make sure your gutter is big enough.

My thinking, however, is why not come out with 3 - 2" conduits and run them over the 10' distance you are going and into whatever you are installing there (Discon's or whatever)?

You can't put all those conductors in one 3" conduit without derating them! The max length you can go without derating is 24"'s.
You need three seperate conduits. Big pipe is for big wire, not for many conductors.
Anytime you have more than 3 current carrying conductors in a raceway you have to derate them. See Chapter 3 in the NEC right before Table 310-16. There are notes there and a table showing you what %'s you would have to derate. And, you would have to go to chapter nine to see if you can even fit that many 3/0's in a 3" (never mind derating).

Unless I'm misunderstanding you, I would come out of the meter and hit my mains right there with seperate conduits. You can derate your neutral (by Code) but in practice you are probably better off not derating it.

Also, you need your MAIN(s) to be right there at the meter. You can't run your feeders unprotected (unfused) any distance at all except a back to back service for example. If you can't accomplish this you'll have to buy a MAIN for the service and then branch out.

A 6x6 sounds too small to me for all those conductors... You're going to have to do the calculations and make sure.

#42096 - 09/17/04 06:09 PM Re: 400 amp service
Merlin Offline

Registered: 01/27/04
Posts: 170
Loc: NW Indiana
Thanks CJS for your knowledge. I was in a hurry to get supplies ordered for installation this week. I was looking all this up but that all takes time. I thought by chance someone would know off of the top of their head. I have researched all this, and have changed a few things. Kinda like any other job, you think you know what you need until you lay it all out and then decide a better way. Thanks again CJS.


[This message has been edited by Merlin (edited 09-19-2004).]


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