Why does the NEC omit 600kcmil MV conductors?

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Woobie

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Los Angeles, CA
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Electrical Engineer
I recently noticed that the NEC MV ampacity tables omit the 600kcmil wire size. I find this curious because 600kcmil is a common LV conductor size. Does anyone know why they omit this?

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Is 600 kcmil really a common size? I looked at two different manufacturers and their cables sizes excluded 600 kcmil.
 
Woobie said:
Sorry, common size for LV cabling, not MV. I'm wondering why the manufacturers would skip 600MCM on MV cabling.
Click to expand...
Sorry, yes you did say that. I wonder what came first the code table or what size are the MV cables that had been traditionally manufactured. In the table you posted there is also 300 and 400 kcmil missing which are both common LV sizes.
 
Woobie said:
I recently noticed that the NEC MV ampacity tables omit the 600kcmil wire size. I find this curious because 600kcmil is a common LV conductor size. Does anyone know why they omit this?
Click to expand...
Unless I missed something in the code (if so will get swiftly corrected) you can specify any conductor size you want under engineering supervision, your not limited to the sizes in the tables, it just has to be expressed in or converted to kcmil (110.6) and a NEC recognized type of insulation if insulated and the termination will have to obviously be compatible in mechanical size and temprature rating (110.14).
For example say I want to use 535 kcmil DLO cable (a common size) thats also rated RHH, I can use southwire's engineers computation for the ampacity at 643 amps for 75C terminations.
Same with common size metric wires that have a listed RHH/RHW or other NEC type insulation.
Same with square or rectangular copper busbar.
etc.
 
tortuga said:
Unless I missed something in the code (if so will get swiftly corrected) you can specify any conductor size you want under engineering supervision, your not limited to the sizes in the tables, it just has to be expressed in or converted to kcmil (110.6) and a NEC recognized type of insulation if insulated and the termination will have to obviously be compatible in mechanical size and temprature rating (110.14).
For example say I want to use 535 kcmil DLO cable (a common size) thats also rated RHH, I can use southwire's engineers computation for the ampacity at 643 amps for 75C terminations.
Same with common size metric wires that have a listed RHH/RHW or other NEC type insulation.
Same with square or rectangular copper busbar.
etc.
Click to expand...
I assume this is a flavor of 310.14(B) (or 315.60(B) for MV)? In any case, my question was more along the lines of wondering why manufacturers don't make 600kcmil MV-105 (or 300kcmil or 400kcmil per infinity's post).

e.g. Southwire:
1763008985870.png
 
infinity said:
Sorry, yes you did say that. I wonder what came first the code table or what size are the MV cables that had been traditionally manufactured. In the table you posted there is also 300 and 400 kcmil missing which are both common LV sizes.
Click to expand...
True, I didn't see that. I'd imagine the manufacturing tradition came first. Maybe it's just too expensive to make and less granular ampacities are needed at the MV level to make it worth it.
 
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