Sizing Parallel Conductors

[MDCodeRed13]

I'm running three phase power with neutral from 440KVA transformer to an 800 amp breaker. Secondary side of transformer is 400VAC. I'm trying to decide if I should run double or triple parallel conductors. It's a short run of about 25'. I've looked at the tables and charts but get confused in trying to figure my conductor sizes. I would be grateful for some help. Thanks in advance!

 

[infinity]

For me 800 amps = 2 sets of 600 kcmil copper to the OCPD.

Welcome to the forum.

 

[Julius Right]

It depends if it the installation conditions are according to Table 310.15(B)(16) and all the single core cables are bonded together so a 80% factor it has to be employed for 6 loaded conductors then you need 2 parallel of 700 MCM copper or according to 392.80 (A)/2/(d) Where single conductors are installed in a triangular or square configuration in uncovered cable trays, with a maintained free airspace of not less than 2.15 times one conductor diameter (2.15 × O.D.) of the largest conductor contained then you need two parallel of 400 MCM copper only.

 

[electrofelon]

I'm running three phase power with neutral from 440KVA transformer to an 800 amp breaker. Secondary side of transformer is 400VAC. I'm trying to decide if I should run double or triple parallel conductors. It's a short run of about 25'. I've looked at the tables and charts but get confused in trying to figure my conductor sizes. I would be grateful for some help. Thanks in advance!

I might run 4 sets of 250 AL. Its somewhat of a personal preference. The more sets you have, the more ampacity per unit conductor area you get so you utilize the conductors more efficiently, but then you have more raceways, parts, and more terminations, even though everything is smaller. I tend toward more smaller sets because I am a one man band and dont usually have help.......3 sets of 400 AL would work too....some of the less common wire sizes might not be readily available, so that could determine things if you dont want to order it in.