Current Carrying Conductors

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jj113054

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? Neutral conductor ? unbalanced loads [310.15(B)(4)(a)]
A neutral conductor that carries only the unbalanced current from other conductors of the same circuit is not considered a current-carrying conductor (Fig. 4 on page 48).


In a hospital with a 3PH/4w (with 200% neutral)/120/208-volt panel , with a TVSS, with separate striped neutrals for each phase, IS the neutral considered a current carrying conductor??
If so, what is the explanation for the above?
Thanks for your time
This answer may resolve a lot of issues out here.
Sincerely, JJ
 
A MWBC from a 208Y/120 volt panel with three phase conductors and a neutral would be 3 CCC's. The neutral in that case would not count as a CCC. When each phase conductor has it's own grounded conductor each conductor would be a CCC.
 
A very typical figure. Now could you explain what this means?

3PH/4w (with 200% neutral)/120/208-volt panel , with a TVSS, with separate striped neutrals for each phase
Click to expand...
 
1) Transformer has 200% neutral line & load
2) Panel has 200% neutral line
3) Panel has separate striped neutrals for each phase
 
jj113054 said:
1) Transformer has 200% neutral line & load
2) Panel has 200% neutral line
3) Panel has separate striped neutrals for each phase
Click to expand...

I have never seen this-- do you actually mean there are 3 neutral bars in the panel that are separate from each other.
 
Neutral

Neutral

jj113054 said:
1) Transformer has 200% neutral line & load
2) Panel has 200% neutral line
3) Panel has separate striped neutrals for each phase
Click to expand...

Because of the harmonic loads the transformer supplying the panel has a 200% neutral. Since the transformer is probably "K" rated (old days we just oversized) the feeder neutral would overheat if it was not upsized, so thus a 200% neutral goes to the panel. The panel has a neutral bar that is rated for 200%. Since the Engineer is concerned with the multi-wire branch circuits he/she has specified a separate Grounded Circuit Conductor be installed for each phase conductor of the branch circuit. As Rob has stated if the circuits were 4-wire with a single neutral and the load was not harmonic, then you would not count the neutral with respect to derating. Since each branch phase has a separate Grounded circuit conductor, they are counted with respect to derating. Neutrals carry imbalance, Grounded Circuit Conductors typically carry the same current as the phase conductor. All of this does make the harmonics go away, its just a way of handling the heat generated by the harmonics.
 
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Since all of the circuits have separate neutrals all (EGC's excluded) of the conductors would be considered CCC's.
 
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