800 Amp 3 Phase Service

[infinity]

No different than adding any loads to an existing service or feeder...you have to do a new load calculation.

I was getting at the fact that a reduced size neutral for a service may turn out to be a very poor design. I'm thinking that adding additional loads in the future may not be possible without increasing the neutral size.

 

[LarryFine]

I was getting at the fact that a reduced size neutral for a service may turn out to be a very poor design. I'm thinking that adding additional loads in the future may not be possible without increasing the neutral size.

But cutting the ungrounded conductors that close (however close "that close" is) to their max ampacity would raise the same concerns. I think that's what Don was saying in post #18, also.

 

[George Stolz]

Have you ever seen prints call for a neutral smaller than the phase conductors?

 

[don_resqcapt19]

I was getting at the fact that a reduced size neutral for a service may turn out to be a very poor design. I'm thinking that adding additional loads in the future may not be possible without increasing the neutral size.

Yes, that could be, but that is a design issue and not a code issue.

90.1(B) Adequacy. This Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance results in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use.

 

[don_resqcapt19]

Have you ever seen prints call for a neutral smaller than the phase conductors?

Not in a long time, and the only time I saw it was for a 240/120 wild leg service. There were 3 sizes specified...A and C phase the largest, neutral next and B phase the smallest. The service disconnect was a fused switch with a smaller fuse for B phase.

 

[jrannis]

I come up with a Neutral (Unbalanced load) of approximately 280 Amps. So if I call it 400 Amps and run two 4/0s (One per run) it will keep me at 7 wires per run and should not be a problem with conductor ampacity. The majority of my loads is a 200Amp 3 Phase Heater and about a dozen 3 phase motors Most of which are 30FLA and 2-3 are 5.5 FLA and a little HVAC(not 3 phase). Does anyone see a problem with this?

Im really no a big fan of reducing the neutral on a wye system. I usually would consider increasing it,
http://books.google.com/books?id=aT...&oi=book_result&resnum=10&ct=result#PPT119,M1

 

[iwire]

Im really no a big fan of reducing the neutral on a wye system. I usually would consider increasing it,
http://books.google.com/books?id=aT...&oi=book_result&resnum=10&ct=result#PPT119,M1

For a service reduce away, there are very few buildings where the major portion of the entire building load is non-linear.

 

[Beem]

BY using T. 310.15(B)(2)(a) You only get 182 amps per unground conductor. Which would bring you up short of your 800a service. Two conduits 8 current carying conductors per.

260A x 70% =182A

Also look at 310.15(B)(2)(c) for possible derate due ambient temperature due to exposure to sun. Of course this depends on how the conduit to the weather head is routed.

 

[djcrzysounds@yahoo.com]

BY using T. 310.15(B)(2)(a) You only get 182 amps per unground conductor. Which would bring you up short of your 800a service. Two conduits 8 current carying conductors per.

260A x 70% =182A

Also look at 310.15(B)(2)(c) for possible derate due ambient temperature due to exposure to sun. Of course this depends on how the conduit to the weather head is routed.

Correct however I just got the prints from the engineer. They call for 3/0 THWN-2 UMMM do I sense a change order in the near future??? Its still the original way I figured however I think I'm going to step away from the table. Not my engineer and I don't need the headaches from this job anymore.