Parallel conductors

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RAHCE

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The Code (NEC 310.4) requires conductors run in parallel to "be of the same length". Is there a requirement to how much of a difference the conductor length can be between the longest to shortest. Example. If I had 10 conduits filled with 600 mcm copper between a pad mounted transformer and a switchgear there is bound to be a "short" leg and a "long" leg. Does the code speak to this?
 
RAHCE said:
The Code (NEC 310.4) requires conductors run in parallel to "be of the same length". Is there a requirement to how much of a difference the conductor length can be between the longest to shortest. Example. If I had 10 conduits filled with 600 mcm copper between a pad mounted transformer and a switchgear there is bound to be a "short" leg and a "long" leg. Does the code speak to this?
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It is describing an 'ideal' objective and one we should attempt to comply with to the greatest extent practical (with practical being the key word)

eg: The short runs to/from a transformer are much more practical to do equally than the 200 foot (or more) feeds. And the shorter the run the more critical it will be to comply.
 
If you apply the code rule as written, you cannot install parallal conductors as it is impossible for them to be the same length. As a practical matter as long as the conductor (shortest) with the lowest impedance is not overloaded there should be no problem. This issue was discussed here as well as in other theads on this forum.
Don
 
It really amounts to a tolerance issue. 5% or less difference in length would be acceptable, at least in my opinion.

Edit: Actually, 5% is conservative but it's easy enough to accomplish so it ought to be met.
 
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There is one more item being overlooked. This code has more to do with LONG runs say a 480V line going up the mountain for a chair lift ect. AC power has a wavelength all-be-it a very long wavelength. if one of the conductors get to be 25% longer or shorter wave (I think this is the number) it will look to be a short to THE SAME PHASE conductors. (remember tuning an antenna for all the CB and HAM raido back in the 70's)


Ken
 
You're talking about the SWR (Standing Wave Ratio). It would be impossible to bring such a phenomenon (i.e., a 25% (i.e., 1/4-wavelength) error) into effect on a compliant power-cable installation.

I'm not sure it would matter even if you did at such low impedances.
 
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