Neutral wire - CCC determination

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Plano12345

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Not sure if I'm in the right forum.

State of Texas
Highway illumination
single phase using 240/480 service

in Texas, lighting is typically on 480 V. We have two wiring options for roadway lighting.
1. 2 hots and a ground
2. 2 hots, a neutral, and a ground

The neutral allows dropping down to 240 for certain lights along your run, like for an underpass.

question: based on the NEC 2011, is the neutral a CCC based on what I described. Please go into detail regardless of the answer. This neutral concept confuses me at times, and I'm not sure when its a CCC when it comes to derating. I read the section in the NEC but I'm simply a novice in some areas.

Example: i have a conduit with 11 conductors on 4 circuits. 2 of the 4 are from description 1 (2 hots x 2). The other 2 are from description 2 (neutral and 2 hots x 2). One of the 2 circuits with the neutral only powers lights using 240. The other has lights being powered at both 480 and 240, varying by location. The final conductor is the one for grounding. Question is how many are CCC? Either the answer is 10 or 8, and I know that alters whether I use 70% or 50% for derating.

thanks in advance and I will provide more info or clarity as needed.
 
Since it's a 1? service and if the neutrals are part of a MWBC they do not count as CCC's.
 
If the neutrals only carry imbalanced current from other conductors they do not count as current carrying conductors for the purpose of ampacity adjustments. In your case two of those neutrals are not carrying imbalance current, and two are. The ones that are common to both ungrounded (sharing the neutral on same circuit) conductors are the ones that only carry unbalanced current.

The concept here is determining how much heat will be produced within a raceway or cable. If line 1 is loaded to 10 amps and line 2 is loaded to 15 amps the common neutral of this will only carry the imbalance of 5 amps. Put same loads on two hots and two neutrals and you have two conductors carrying 10 amps and two conductors carrying 15 amps. Which one do you see contributing more heat to the raceway temperature?

Note this does not work this way for two lines and neutral of a three phase Y system, as the neutral does not carry imbalanced current in that instance, but it does work with a Y where all three phases are used.

Where the neutral is carrying imbalanced current the neutral will never introduce more heat in the raceway than the net load on the ungrounded conductors introduces.

High harmonic producing loads is also another exception where the neutral will not be carrying unbalanced load.
 
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