So are residential neutrals considered current carrying or not?

[tbartek]

I'm new to the forum so I'm sure this has been covered before. But, searching through the posts there seems to be conflicting opinions. I know that according to 310.15(B)(5)(b&c) that these neutrals are current carrying. But once and for all, are the neutrals in a residential service considered current carrying or not, for purposes of derating when bundling conductors? Have I been teaching this properly to say they are not, or do I owe twenty years worth of "never mind" to my students?

 

[raider1]

Welcome to the forum.

For a typical single phase 3 wire service to a home, the Neutral in the service would not be counted as a CCC for ampacity adjustments in accordance with 310.15(B)(5)(a) as the neutral only carries the unbalanced current from ungrounded conductors.

Chris

 

[augie47]

A neutral conductor that carries only the unbalanced current on a 240/120 system such as probably 95+% of your residential services is not considered a current carrying conductor for the purpose of 310.15(B)(4).
When you mention "bundling" in residential wiring, I think more of branch circuits where a number of 2 conductor cables might be bundled. In those situations, since the neutral of a two wire circuit carries 100% of the load, derating would br required.
Does that answer your question ?

(Sorry Chris, I was slow thinking/typing/posting)

 

[infinity]

For the service mentioned they are not considered to be current carrying.

 

[GoldDigger]

For the service mentioned they are not considered to be current carrying.

The reason being that for a three wire 240/120 service or for a four wire 120/208 service any current flowing in the neutral will be matched by a corresponding reduction below maximum value in the current carried by one or more of the phase wires.

 

[infinity]

The reason being that for a three wire 240/120 service or for a four wire 120/208 service any current flowing in the neutral will be matched by a corresponding reduction below maximum value in the current carried by one or more of the phase wires.

If you had a shared neutral and two phase conductors from a 208Y/120 system the neutral would be considered current carrying since it would carry about the same current as the phase conductors.

 

[tbartek]

A neutral conductor that carries only the unbalanced current on a 240/120 system such as probably 95+% of your residential services is not considered a current carrying conductor for the purpose of 310.15(B)(4).
When you mention "bundling" in residential wiring, I think more of branch circuits where a number of 2 conductor cables might be bundled. In those situations, since the neutral of a two wire circuit carries 100% of the load, derating would br required.
Does that answer your question ?

(Sorry Chris, I was slow thinking/typing/posting)

I guess the way I worded it, it was confusing. I was referring to the branch circuit conductors. So 120V 2/wire circuits neutrals count. Multiwire circuits neutrals wouldn't and 240V 3/wire circuits neutrals wouldn't.

 

[roger]

I guess the way I worded it, it was confusing. I was referring to the branch circuit conductors. So 120V 2/wire circuits neutrals count. Multiwire circuits neutrals wouldn't and 240V 3/wire circuits neutrals wouldn't.

Here are a couple simple illustrations that apply to your scenarios

In a two wire circuit the grounded conductor carries the same current as the ungrounded conductor

In an unbalanced MWBC the neutral carries the unbalanced current.

Roger

 

[jumper]

You might find this helpful. Rob/Infinity wrote it in another thread.

Here's some examples of when to count the neutral as a CCC:

208Y/120 volt system-different circuit types:

A)- 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
B)- 3 wire circuit w/ 2 ungrounded, 1 neutral = 3 CCC's
C)- 4 wire circuit w/ 3 ungrounded, 1 neutral = 3 CCC's*

Notes:
A)- A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
B)- In this circuit the neutral current will be nearly equal to the current in the ungrounded conductors so the neutral counts as a CCC
C)- In this circuit the neutral will only carry the imbalance of the current between the three ungrounded conductors so it is not counted as a CCC, with one exception, *if the current is more than 50% nonlinear then the neutral would count as a CCC.

120/240 volt system-different circuit types:

D)- 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
E)- 3 wire circuit w/ 2 ungrounded, 1 neutral = 2 CCC's

Notes:
D)- A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
E)- In this circuit the neutral will only carry the imbalance between the two ungrounded conductors so the neutral is not counted as a CCC.