HVACR/motor application: de-rating from table 310.15(C)(1) as 4-con necessary with N?

[rh2]

Hi,

I'm developing some schematics for an HVACR application utilizing semi-hermetic recip compressors and condenser fans. I'm trying to better understand the rules of needing to count the neutral conductor as one of the current-carrying conductors discussed throughout the book. I'm really trying to avoid needing to count the neutral as a current-carrying conductor as the (3-phase) motor of course doesn't require it, but unfortunately the documentation for the compressor motor's onboard diagnostic module shows its primary connection as L3 and N. I did read the FAQ on the forum notes but I'm not 100% on the language of balanced/unbalanced and also on 310.15(E)(3).

So to start, 310.15(E)(1):

"A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(C)(1)."

This to me sounds like a positive, as the onboard diagnostic module uses L3 and N, but also of course pales in comparison as a % of total load. I think it's 1-3 VA continuously. This sounds like what is described above. But 310.15(E)(3) also mentions this:

"On a 4-wire, 3-phase wye circuit where the major portion of the load consists of nonlinear loads, harmonic currents are present in the neutral conductor; the neutral conductor shall therefore be considered a current-carrying conductor."

Should I be worried about this for my project, or can I go ahead and just not derate what I'm running in the conduit, at least from a Table 310.15(C)(1) perspective?

Thanks!

 

[infinity]

"On a 4-wire, 3-phase wye circuit where the major portion of the load consists of nonlinear loads, harmonic currents are present in the neutral conductor; the neutral conductor shall therefore be considered a current-carrying conductor."

The major portion is more than 50%. Nothing in your application would have more than 50% of the load as nonlinear so the neutral does not count as a CCC.