neutral current carrying

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shaw0486

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Can some one explain this article to me because nec article 310.15b4a states that a "neutral that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when apply the provisions of 310.15b2a.

Is this saying that if i have a 3/4" emt i can run (2) # 12 thhn one being a hot and one being the neutral do i count that neutral as a current carrying conductor?
 
310.15(B)(4) Neutral Conductor.
(a) A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(B)(2)(a).
(b) In a 3-wire circuit consisting of two phase conductors and the neutral conductor of a 4-wire, 3-phase, wye-connected system, a common conductor carries approximately the same current as the line-to-neutral load currents of the other conductors and shall be counted when applying the provisions of 310.15(B)(2)(a).
(c) On a 4-wire, 3-phase wye circuit where the major portion of the load consists of nonlinear loads, harmonic currents are present in the neutral conductor; the neutral conductor shall therefore be considered a current-carrying conductor.
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In a two wire circuit the neutral is a CCC because it carries the same amount of current as the hot conductor. In a MWBC the neutral may only carry the unbalanced current. Those conditions are outlined above.
 
Can any one explain what 310.15b4a is saying or give an example because it was a subject in class tonight and didnt quite understand
 
If you had a multiwire branch circuit from a single phase 120/240 volt system that consisted of two hot legs and one shared neutral conductor that neutral conductor would be only carrying the unbalanced current from the two hot conductors of the same MWBC.
 
shaw0486 said:
Is this saying that if i have a 3/4" emt i can run (2) # 12 thhn one being a hot and one being the neutral do i count that neutral as a current carrying conductor?
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Shaw, in a 2 wire circuit, there is no "neutral", there is a grounded conductor. (Yes, it is common to refer to it as a neutral) Both conductors carry the same amount of current, therefore they are both CCCs (current carrying conductors)

If you had a 3-wire circuit (120/240 v, 1 phase) or a 4-wire circuit (208/120 v 3 phase), then that grounded conductor is a neutral that meets the criteria of 310.15(B)(4), and does not need to be counted as a CCC.
 
If your draw a single line diagram, consider it either AC or DC, and you take into account the application of electric work, and even account for the various parts along this service(metering)! Assume a device or another application, etc., this is where a potional of the unbalanced load might be produced.

There's nothing neutral in any of it, I never consider it other than Live!
 
infinity said:
If you had a multiwire branch circuit from a single phase 120/240 volt system that consisted of two hot legs and one shared neutral conductor that neutral conductor would be only carrying the unbalanced current from the two hot conductors of the same MWBC.
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It's important to remember that this does not apply to a 120/208 single-phase service. (Yes, I know you said 120/240 and I'm sure you know the difference.)
 
guess what?

guess what?

On a 120/240 sytem I can run 8 #12 thhn and 4#12 thhn (copper) in the same conduit. The conductors to serve 8 - 120v lighting or outlet circuts as long as the first 8 #12 are evenly paired A phase / B phase.
 
Bill Davis said:
On a 120/240 sytem I can run 8 #12 thhn and 4#12 thhn (copper) in the same conduit. The conductors to serve 8 - 120v lighting or outlet circuts as long as the first 8 #12 are evenly paired A phase / B phase.
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Yes, that would be 4 MWBC's which would be 8 CCC's. After derating (70%) your adjusted ampacity for #12 THHN would be 21 amps.
 
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