NEC 2014 section 705.12(A) and output conductors

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hhsting

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Glen bunie, md, us
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Please see attached sketch. I have incoming 3 sets of 4#350kcmil incoming from utility to 800A service disconnect 208/120V three phase.

I have line side connection from 800A service disco to solar AC disco #1 400A and from 800A service disco to solar AC disco #2 400A. The lines side conductor tap from line side of service disco to solar AC #1 is 8#4/0 in one 4 inch conduit. The line side tap from service disco to solar AC #2 is 8#4/0 in one 4 inch conduit.

Questions:

1. For conductors from 800A service disco to solar AC Disco#1 that are 8#4/0 in one 4 inch conduit includes two phases A, two phase B, two phase C and two neutrals in one conduit. I don’t think you can put phase conductors of parallel sets in one conduit however I am not sure what would NEC 2014 code would apply to these solar AC output conductors?

2. Although solar AC #1 and solar AC #2 disconnects each 400A overcurrent add up to 800A which is the service rating, I am not sure it would comply per NEC 2014 705.12(A) or other section.

I have 3 sets of 350kcmil coming in. For both solar AC#1 and solar AC #2 disconnects each has 8#4/0. So that’s 16#4/0 total and of them 12#4/0 are phase. So this means Phase A conductors have 4#4/0 and if they are tap from 3 #350 kcmil phase A service this means one phase A service conductor would have 2#4/0 which would exceed ampacity of 350kcmil. Same thing with Phase B and Phase C. I am not sure if this would be not in compliance with NEC 2014 section 705.12(A) or any other NEC 2014 section?
 

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jaggedben

Senior Member
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Northern California
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Solar and Energy Storage Installer
...
1. For conductors from 800A service disco to solar AC Disco#1 that are 8#4/0 in one 4 inch conduit includes two phases A, two phase B, two phase C and two neutrals in one conduit. I don’t think you can put phase conductors of parallel sets in one conduit however I am not sure what would NEC 2014 code would apply to these solar AC output conductors? ...

There is no requirement that parallel conductors be in separate conduits. It is usually done for practical reasons, not code reasons. Regardless, the same relevant code sections in Chapter 3 would apply to solar AC output conductors as to any others.

2. Although solar AC #1 and solar AC #2 disconnects each 400A overcurrent add up to 800A which is the service rating, I am not sure it would comply per NEC 2014 705.12(A) or other section.

I have not checked any math on the ampacities of the conductors you've mentioned. However, if the service is rated 800A then it would be allowed to be backfed by solar outputs whose required OCPDs do not exceed 800A in total. That is precisely what NEC 2014 705.12(A) says, and precisely the section that governs that question.
 

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
1. For conductors from 800A service disco to solar AC Disco#1 that are 8#4/0 in one 4 inch conduit includes two phases A, two phase B, two phase C and two neutrals in one conduit. I don’t think you can put phase conductors of parallel sets in one conduit however I am not sure what would NEC 2014 code would apply to these solar AC output conductors?

Are these copper or aluminum 4/0? I am assuming copper.
Whats the calculated load for each 400A disco?
Are you 100% sure the neutrals wont carry harmonics or do the inverters have isolation transformers?
 
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