current carrying conducter

[rubydew02]

What is the defintion of a current carring conducter and do you count a neutral as a current carrie

 

[augie47]

Any conductor can be a current carrying conductor. Your question I believe references 310.15(B)(2) & (B)(4) {08} which deals with counting a neutral as a current carrying conductor when derating for raceway fill.
You really need to look at 310.15(B)(4) as there are several aspects to the answer such as the type system (single phase vs 3 phase) and which phases are in use and if the majority of the load is linear or nonlinear.

 

[Dennis Alwon]

What is the defintion of a current carring conducter and do you count a neutral as a current carrie

This is general information on the subject.

In a 2 wire 120V branch circuit the neutral is a current carrying conductor (CCC). In a single phase panel where you have a multiwire branch circuit (MWBC) then the neutral only carries the unbalanced load between the phases so the neutral is not considered a CCC simply because the 3 wire circuit will never carry more than what the 2 hot conductors are capable of carrying.

Say we have a single phase system and you run a MWBC to receptacles. This circuit has the capacity of 20 amps per phase. If one phase draws 10 amps and the other draws 18 amps then the neutral draws 18-10 or 8 amps. If both draw 20 amps the neutral draws 0. In no case will the total amp draw be more than the 20 amps on both ungrounded conductors, thus the neutral does not count.

Now if you have a 3 phase system with a 4 wire MWBC then the neutral does not count either. If it is 3 phase and you have only a 3 wire MWBC then the neutral counts.

Things change with nonlinear loads such as fluorescents lights, etc.

 

[petersonra]

What is the defintion of a current carring conducter and do you count a neutral as a current carrie

I would not count a control circuit as "current carrying", such as a solenoid valve. Technically there is some current when the solenoid valve is on, but it is not usually very much.

I do not recall there is a definition of this in the code, but from context, it is clear that heat from I^2R losses are the issue, and with minimal current there is minimal heat, so it seems reasonable to consider it as non-current carrying.

I typically go by how many branch circuits are involved. If I have 15 wires on the same fuse, I am not going to count all 15 of them as current carrying. As far as I am concerned, it is one CCC.

 

[bullheimer]

what dennis said, along with control wires. ps to be in the same raceway the control wire conductor's insulation has to be rated at 600V

 

[roger]

what dennis said, along with control wires. ps to be in the same raceway the control wire conductor's insulation has to be rated at 600V

That is a common belief but not an accurate statement, read 300.3(C)(1)

Roger

 

[handy10]

This is general information on the subject.

In a 2 wire 120V branch circuit the neutral is a current carrying conductor (CCC). In a single phase panel where you have a multiwire branch circuit (MWBC) then the neutral only carries the unbalanced load between the phases so the neutral is not considered a CCC simply because the 3 wire circuit will never carry more than what the 2 hot conductors are capable of carrying.

Say we have a single phase system and you run a MWBC to receptacles. This circuit has the capacity of 20 amps per phase. If one phase draws 10 amps and the other draws 18 amps then the neutral draws 18-10 or 8 amps. If both draw 20 amps the neutral draws 0. In no case will the total amp draw be more than the 20 amps on both ungrounded conductors, thus the neutral does not count.

Now if you have a 3 phase system with a 4 wire MWBC then the neutral does not count either. If it is 3 phase and you have only a 3 wire MWBC then the neutral counts.

Things change with nonlinear loads such as fluorescents lights, etc.

It is certainly is clear that the code says that a neutral in a MWBC is not counted as current carrying. However, to use the 20 amp example if none phase is carrying 20 amps and the other is carrying 0, then the neutral is carrying 20 amps. So, my question is: why should the neutral not be considered a CCC?

 

[Dennis Alwon]

It is certainly is clear that the code says that a neutral in a MWBC is not counted as current carrying. However, to use the 20 amp example if none phase is carrying 20 amps and the other is carrying 0, then the neutral is carrying 20 amps. So, my question is: why should the neutral not be considered a CCC?

Neutrals do carry current however they carry no more than the 3 non grounded conductors together. Read this thread from our FAQ's and see if that helps.

 

[hurk27]

It is certainly is clear that the code says that a neutral in a MWBC is not counted as current carrying. However, to use the 20 amp example if none phase is carrying 20 amps and the other is carrying 0, then the neutral is carrying 20 amps. So, my question is: why should the neutral not be considered a CCC?

because if one is carrying current the other cant the balance between the two will not exceed the rating of one conductor, it is kind of like a 3-way one traveler at a time can be carrying current.

 

[handy10]

Neutrals do carry current however they carry no more than the 3 non grounded conductors together. Read this thread from our FAQ's and see if that helps.

Thanks for the link. It is well written.

 

[hurk27]

I want to add that in a 3 phase WYE system and you only use 2 phases and the neutral then the neutral will count as a current carrying conductor, 310.15(B)(4)(b)

 

[mlnk]

Seems to me that every inspector believes that every wire counts as a current carrying conductor except the grounding wire.

 

[petersonra]

Seems to me that every inspector believes that every wire counts as a current carrying conductor except the grounding wire.

A lot easier to count them that way.

 

[augie47]

Seems to me that every inspector believes that every wire counts as a current carrying conductor except the grounding wire.

In our State there are a number of electricians that were "grandfathered in" once testing was required. Sometimes, after trying to explain a ccc for the 15th time, it's easier just to tell them to count all as ccc unless they can show you why they shouldn't.