parallel conductors

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Charlie Bob

Charlie Bob

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West Tennessee
The NEC 310.4 (A) states that conductors in parallel should be the same length and the same conductor material. . . i thought i knew that rule and how to aplly it, but doing some reading oer the weekend put some doubts in me. I read that the above mention rule aplies to a "parallel set". . now here's where the terminollogy gets in the way. . what do you call a parallel set?. . . are each individual phases and grounded conductor consider a "set" or you consider a set all the conductors in the same conduit a set?
I always thought that one set was the phases and grounded conductor in the same raceway. . .
 
As long as the pair that feeds a phase has the same characteristics you are good. So Phase "A" can have a pair of 4/0 THHN wires and the pair that feeds phase "B" can have THW insulation. You cannot have thw and a thhn feeding in parallel.
 
Here is the wording from the 2011


310.10(H)

(2) Conductor Characteristics. The paralleled conductors
in each phase, polarity, neutral, grounded circuit conductor,
equipment grounding conductor, or equipment bonding
jumper shall comply with all of the following:
(1) Be the same length
(2) Consist of the same conductor material
(3) Be the same size in circular mil area
(4) Have the same insulation type
(5) Be terminated in the same manner
Click to expand...
 
Dennis Alwon said:
As long as the pair that feeds a phase has the same characteristics you are good. So Phase "A" can have a pair of 4/0 THHN wires and the pair that feeds phase "B" can have THW insulation. You cannot have thw and a thhn feeding in parallel.
Click to expand...

Thanks Dennis that clarifies my confusion. . .:thumbsup:
 
Are you also asking if you can parallel from the same conduit?Meaning mutiple conductors in one run and used as a paralleled pair.
 
The reasoning is that you want each element of the parallel conductor to have the same resistance so that they will all carry same amount of current. If one has a lower resistance it will carry more current. Lets say you have a 200 amp conductor that is part of a 400 amp parallel set that carries well over 200 amps because it has a lower resistance than its mate. I think you get the idea of what could happen from there.
 
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