Code Clarification 310.15 (B) (5) (a) Neutral Conductor

[he1029]

”(5) 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)(3)(a).”

My question is basically when is it called the “SAME CIRCUIT”
Is this only relevant when it's connected to any single device? i.e. a Panel, ac, appliance?
Or is it also at any multi wire branch circuit?
In other words what is the definition of “SAME CIRCUIT”

This came up at a code refreshing course last night, and it went back and forth
I would appreciate your input on this

Thanks all

 

[roger]

It is any Multi Wire Circuit, it could a service or branch circuit.

Roger

 

[kwired]

Two wire circuit - there is no unbalance current - both conductors are current carrying

Multiwire circuit - some can have only unbalance current on neutral some do not.

Single phase three wire (such as 120/240) the neutral only carries unbalance current.

Three phases plus neutral from a wye secondary the neutral only carries unbalance current.

Two phases plus neutral from a wye secondary the neutral carries about same amount of current as highest loaded phase conductor.

Having a lot of harmonic producing loads can change this though.

 

[ActionDave]

My question is basically when is it called the “SAME CIRCUIT”
Is this only relevant when it's connected to any single device? i.e. a Panel, ac, appliance?
Or is it also at any multi wire branch circuit?
In other words what is the definition of “SAME CIRCUIT”

A multiwire branch circuit is a circuit. The conductors of a MWBC don't all have to go to the same device for it to be the same circuit.

You have four wires, A,B,C and a noodle; it doesn't matter how many different lights those conductors go to, the electrons are leaving home and coming back (i.e. completing the circuit) on the same four wires.

 

[GoldDigger]

Looking at another way, a branch circuit consists of all of the conductor downstream of the branch OCPD.
If it is not a branch OCPD, all the conductors downstream as far as the next OCPD(s) are a feeder circuit

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