310.15 (4) (a)

[steveonb]

310.15 (4) (a) says "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). )
If you had a separate neutral conductor for each circuit would you have to count the neutral as current carrying?

 

[raider1]

If you had a separate neutral conductor for each circuit would you have to count the neutral as current carrying?

Yes, in the case of a 2 wire circuit( 1 ungrounded conductor and 1 neutral), the neutral will carry the same amount of current as the ungrounded conductor.

The intent of 310.15(B)(4)(a) is that when you have a multi-wire branch circuit the neutral will only carry the unbalanced load between the ungrounded conductors and therefore the heating of the neutral will be such that it won't need to be counted as a current carrying conductor.

Chris

 

[Mayimbe]

it depends on what do you need to do. if it is for ampacity calc, you have to count the neutral as current carrying. if it is for load flow calc, you dont.

 

[LarryFine]

If you had a separate neutral conductor for each circuit would you have to count the neutral as current carrying?

Yes, as above, and both of them. A 3-wire MWBC on 120/240 1ph counts as two, while the same two circuits count as four. For a 3ph MWBC, it's three vs. six. That's why we die-hards like them so much.


Added: That's just one of many reasons, actually.

 

[LarryFine]

... when you have a multi-wire branch circuit the neutral will only carry the unbalanced load between the ungrounded conductors and therefore ... it won't need to be counted as a current carrying conductor.

Right. For each amp the neutral is carrying, that's one amp we know will not be flowing on a line conductor.