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What is the proper application of 2014 NEC 250.24(C)(2)?

Question asked by patrick.fagerman on Jun 14, 2018
Latest reply on Jun 18, 2018 by fanchier

I think I can best express my question in the following Scenario: 

Scenario:

1600A, 480v, 3-phase service entrance main breaker with only 3-phase loads is to be fed from a 480/277V, 3-phase utility transformer via (5) runs of 3#400kcmil THWN/THHN conductors.

 

Question:

What is the required size of Grounded Conductor required in each raceway (conduit) serving the service entrance? More specifically, is the Total kcmil area (in this code section) referencing to parallel within a given conduit or to the collective set of parallel conduits carrying individual sets of conductors (not parallel)? See below for code references.

 

Concern:

I want to ensure I am properly applying 2014 NEC 250.24(C)(2). The title is “Parallel Conductors in TWO or MORE Raceways”.

 

Understanding and Confusion:

Code Understanding:  Each raceway (conduit) has One set of Ungrounded Conductors (not parallel within a given conduit).

 

Code Understanding:  Each raceway (conduit) is to have a Grounded Conductor (parallel to that in the other conduits).

 

Code of Confusion (to me):  The size of Grounded Conductor in each raceway (conduit) shall be based on the TOTAL cmil area of the PARALLEL Ungrounded Conductors in the ‘RACEWAY’, as in (C)(1), but smaller than 1/0 AWG.

 

CONFUSION: So given that there are no Parallel conductors within a given raceway (conduit), does this mean that the last noted ‘RACEWAY’ is a collective term for the set of parallel raceways and is subject to the 1/0 minimum and the Table 250.102(C)(1) minimum for Over 1100 kcmil?

 

My confusion expressed in Result Choices:

Result 1: If I consider the Parallel statement to refer only to cables within each conduit of 400kcmil separately I would have a #1/0 grounded conductor requirement (per table 250.102(C)(1) Over 350 through 600)).

 

Result 2: If I consider the Parallel statement to refer to the multiple raceways (conduits) in parallel or 400kcmil each then I have the 1/0 minimum and the 12.5% rule across the 5 sets in parallel. This would give a 250kcmil grounded conductor requirement in each raceway (conduit).

 

I may be making this more complicated than necessary.

 

Thank you for any help!

Patrick

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