Circuit unbalance code stipulation

[ZeroSeq]

Hello all, I have a basic question regarding low voltage branch circuiting. (moved from Motors section)

Would anyone be able to point me to a code stipulation (NEC) which requires a minimum amount of balance within a three phase branch circuit?

For example, if I had a three phase branch circuit which fed a "black box" (like an industrial process load) that had an inherent load unbalance where the neutral carried up to say, 50% of the max line current, would this be allowable by code?


Thanks,

 

[7anoter4]

In my opinion, NEC does not recommend any voltage unbalance limits-except the voltage drop of 3% per branch or feeder and total 5% for branch and feeder together.
As I know the supply voltage unbalance limit recommendation is in:
American National Standard for Electric Power Systems and Equipment -Voltage Ratings (60 Hz), ANSI C84.1-2006 Annex C (Informative) Polyphase voltage unbalance C.2 Recommendation:
"Electric supply systems should be designed and operated to limit the maximum voltage unbalance to 3 percent when measured at the electric-utility revenue meter under no-load conditions."

 

[waross]

Under neutral conductors you may find a rule to the effect that neutral conductors shall have adequate ampacity to carry any unbalanced currents.
The implied corollary of this is that the current unbalance will be limited by the rated ampacity of the neutral conductors and busses.
It is good practice to connect unbalanced loads on different phases in such a way as to limit the total current unbalance on the panel.
Single phase loads are allowed to be connected phase to phase and, subject to suitable system grounding methods, are allowed to be connected phase to neutral.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[1capybara]

no, not a NEC requirement, but it is best practice to balance loads as much as possible to limit breaker tripping