Raceway wiring

[AlexFaubel]

Referring to 300.20(A), I have a single 800A 480V breaker feeding a distribution block through 3, 3" Ferrous metal conduits, approximatly 25'. This distribution block feeds multiple, lower amperage, fused disconnects. I am feeding the distribution block from the breaker with 9 runs, 3 per phase, of 250MCM. I was told it does not matter if you run each phase through its own conduit or combine 1 run of each phase through the conduits. I interperate the code to say that you must have 1 run of each phase in each conduit, essentially creating a circuit, to minimize induction heating. Am I correct?

 

[raider1]

Welcome to the forum.

You will want to look at 310.10(H) (2011 NEC) for the installation of conductors in parallel, specifically 310.10(H)(3).

(3) Separate Cables or Raceways. Where run in separate
cables or raceways, the cables or raceways with conductors
shall have the same number of conductors and shall have the
same electrical characteristics. Conductors of one phase, polarity,
neutral, grounded circuit conductor, or equipment
grounding conductor shall not be required to have the same
physical characteristics as those of another phase, polarity,
neutral, grounded circuit conductor, or equipment grounding
conductor.

Chris

 

[xformer]

Referring to 300.20(A), I have a single 800A 480V breaker feeding a distribution block through 3, 3" Ferrous metal conduits, approximatly 25'. This distribution block feeds multiple, lower amperage, fused disconnects. I am feeding the distribution block from the breaker with 9 runs, 3 per phase, of 250MCM. I was told it does not matter if you run each phase through its own conduit or combine 1 run of each phase through the conduits. I interperate the code to say that you must have 1 run of each phase in each conduit, essentially creating a circuit, to minimize induction heating. Am I correct?

I would look at 300.20 induced Currents in Ferrous Metal Enclosure or Ferrous Metal Raceways..