Current Carrying Conductor

[shaw0486]

Hi,
I have always been a little unsure on article 310.15(B) (5) (a) neutral Conductors. This is not saying if you are pulling a full boat into a conduit the neutral is not considered current carrying? Right? This is simply stating that if you have a true 3 phase circuit that requires a neutral that circuit neitral can be excluded from being considered a current carrying conductor????

 

[George Stolz]

I'm not sure of the distinction you are making between your two circuits (I'm not seeing a difference), but if you have three phases sharing a neutral then the neutral is usually not a current carrying conductor for the purposes of derating. The four conductors will never generate more heat than three conductors would, due to cancellation.

 

[kwired]

Hi,
I have always been a little unsure on article 310.15(B) (5) (a) neutral Conductors. This is not saying if you are pulling a full boat into a conduit the neutral is not considered current carrying? Right? This is simply stating that if you have a true 3 phase circuit that requires a neutral that circuit neitral can be excluded from being considered a current carrying conductor????

That is correct. Same is true for two opposite lines and neutral on a single phase or on the two 120 volt leads and neutral of a delta with that configuration.

Two phases of a wye system and a neutral is different. The neutral does not carry zero current in this case if the two phases are the same current, instead it carries approximately the same current as the two phases, and has similar heating effect in raceway or cables is why it needs counted as current carrying conductor.

If the neutral is only carrying unbalanced current it is not adding additional heating, any current the neutral is carrying is current that an ungrounded conductor is not carrying, so the net heating effect is no more than the ungrounded conductors if they were balanced.

Hope that makes sense.

 

[kwired]

I'm not sure of the distinction you are making between your two circuits (I'm not seeing a difference), but if you have three phases sharing a neutral then the neutral is usually not a current carrying conductor for the purposes of derating. The four conductors will never generate more heat than three conductors would, due to cancellation.

I don't see any difference either, when people use the term "full boat" they are usually refering to a multiwire branch circuit with three phase conductors and a neutral - I think. Don't here that term around here a lot.