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Scenario:

Say for example you are pulling feeders for a tap box to a meter stack in a condo style hi-rise and you are using parallel runs to get 3 phase 120/208 with 800 amps. It is protected by an 800 amp circuit breaker from the transformer. You've installed 3 x 3" pipes to pull 400 kcmil aluminum wire which is good for 290 amps each. So 3 x 290=870 amps. Sounds good! However, would you also have to derate the wire according to table 5c because the neutral that you are pulling with the 3 conductors would make a total of 4 current carrying conductors? Or does the neutral not count as a current carrying conductor as defined in code rule 4-004(3)?

Questions:

1) How would you interpret this rule given this situation?
2) What is considered an unbalanced load under normal circumstances?
3) Would you have to derate the cable (table 5c 4-6 conductors) to 80% so you would only be getting 696 amps?

4) if I have been unclear in anything please let me know.
 

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A reminder that this is CCE not NEC
 
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Neutral doesn't count on 3-phase 4 wire. It does count on a 3-phase system where two hots and a neutral are used, because the neutral carries more than the unbalanced current. As to item 4 in your post, the question is perfectly clear - and common.
 

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Unless there is some information missing, than I would not count the neutral in your service as current carrying. Conduit fill - yes.
Usually the engineer has calculated the loads and indicated same on your panel schedules.
You would phase balance your loads to insure a balanced neutral. Of course this balance shifts with usage and your unbalanced neutral will fluctuate.
 

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(1) No need to derate 4-004(3)

(2) If there's a neutral, the load will probably be unbalanced on and off under normal conditions but it will never have as much amperage as the phase conductors. It only carries the unbalanced current from the other conductors.
A neutral would not be needed on a perfectly balanced load in theory.

(3) No

(4) Clear as mud :thumbsup:

Arni19 -- D tables are for underground parrallel installations
 
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