parallel conductors

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ipp

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there is a main distributon panel feeding a 3 phase 225kva transformer 480v primary and 208 secondary.feeding the primary there is two sets 250kcm conductors thhn and one #2thhn gnd, over current protection is a 350a breaker. both sets of parallel feeders are in one 3 1/2 piece of greenfield 17 inches long, total lenth of conductors are 6 foot. my questions; can you run both sets in one conduit? or should they be in seperate conduits like ive alwalys done and will they be subjected to overheating if all are together in one raceway?. also if allowed is there any limit on lenth of conductors?
 

roger

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See the notes to tables in chapter 9.

(4) Where conduit or tubing nipples having a maximum length not to exceed 600 mm (24 in.) are installed between boxes, cabinets, and similar enclosures, the nipples shall be permitted to be filled to 60 percent of their total cross-sectional area, and 310.15(B)(2)(a) adjustment factors need not apply to this condition.

I haven't done the calculation to see if the 60 percent is exceeded.

Roger
 

infinity

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Derating wouldn't lower your condcutor ampacity below 350 amps even if you did require derating.
 
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