# Counting neutral as CCC



## J_Captain (Jul 14, 2013)

310.15(B)(5)(a)

I'm getting a little confused interpreting this section. I will be running dedicated neutrals for each circuit. There are no shared neutrals. When reading the code it states that the neutral does not need to be counted as a CCC if it "carries only the *unbalanced current* from other conductors of the *same circuit*."

As I am thinking, a *unbalanced current *on the neutral would come from running a full boat, which would share the neutral between the 3 phases. But that would also mean that the "other conductors of the *same circuit*" would not apply because I have 3 circuits sharing that neutral. 

But for my purpose. Do I need to count the neutrals in my run when each is dedicated to only one circuit?

Thanks for any help.


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## HackWork (Oct 2, 2009)

J_Captain said:


> 310.15(B)(5)(a)
> 
> I'm getting a little confused interpreting this section. I will be running dedicated neutrals for each circuit. There are no shared neutrals. When reading the code it states that the neutral does not need to be counted as a CCC if it "carries only the *unbalanced current* from other conductors of the *same circuit*."
> 
> ...


Remember that as far as the code book the white wire in a 2 wire circuit isn't a neutral, it's a grounded conductor. It's only a neutral in a MWBC.

In a normal 2 wire circuit (a neutral for each hot) the neutral carries the same amount of current as the hot wire. Because of this, you count it as a CCC.

In a MWBC, the neutral only carries the different between the hots. Because of that, you don't count the neutral as a CCC in a MWBC.


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## Dennis Alwon (May 9, 2009)

To add to what Hax wrote

Here is something written by Trevor at Mike HolMike HolMike Holt
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 condcutors so the neutral is not counted as a CCC.


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## KGN742003 (Apr 23, 2012)

J_Captain said:


> 310.15(B)(5)(a)
> 
> I'm getting a little confused interpreting this section. I will be running dedicated neutrals for each circuit. There are no shared neutrals. When reading the code it states that the neutral does not need to be counted as a CCC if it "carries only the *unbalanced current* from other conductors of the *same circuit*."
> 
> ...


Those other 3 circuits you are talking about are actually all part of 1 multiwire branch circuit. If you think about it like that the wording in the code should make sense.


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## TGGT (Oct 28, 2012)

Dennis Alwon said:


> To add to what Hax wrote
> 
> Here is something written by Trevor at Mike HolMike HolMike Holt
> Here's some examples of when to count the neutral as a CCC:
> ...


Would you explain "50% non-linear"?


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## Dennis Alwon (May 9, 2009)

If non linear loads such as fluorescents, computers, etc are greater than of the circuit then the neutral would count even in a multiwire branch circuit. There are times when it is speced that the neutral be larger than the ungrounded conductors because of non linear loads.


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## TGGT (Oct 28, 2012)

Dennis Alwon said:


> If non linear loads such as fluorescents, computers, etc are greater than of the circuit then the neutral would count even in a multiwire branch circuit. There are times when it is speced that the neutral be larger than the ungrounded conductors because of non linear loads.


A "super neutral"?


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## raider1 (Jan 22, 2007)

TGGT said:


> A "super neutral"?


Yes I have heard it termed that.

When you have odd triplen harmonics (Harmonics at the 3rd etc.) the neutral currents actually add instead of cancel themselves out. When you get a large harmonic load the neutral can be overloaded so some engineers specify oversized neutrals to handle the harmonic neutral current.

Chris


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## Carultch (May 14, 2013)

To determine whether or not neutral counts as a "current carrying conductor" for bundling derate purposes, think about the total local heating that will happen in the entire cross section of wires. Heating and temperature ratings are the entire reasoning of sizing wires the way we do.

In circuits where the neutral is guaranteed to carry the same amount of current as the live conductor(s), it must be counted. The example is a typical household circuit, with 1 live and 1 neutral, on a 120/240 system. Most loads are line-to-neutral. Some big loads would be 240 volts connected line to line.

In circuits where all that neutral does, is carry an imbalance of current of a normally balanced circuit among live conductors, the neutral doesn't count as a CCC. You can mathematically show why it doesn't, by setting up situations of current imbalances, and calculating the heat dissipation in each wire. No matter how imbalanced it ends up, any resistive heating in the neutral will not exceed the less resistive heating in the imbalanced phases at lower than max current.

On net, all 4 wires do not carry any more current than the 3 phase wires ordinarily would when fully loaded at balanced load.

When neutral is only used for "instrumentation purposes", such as a voltage reference or effective grounding, it doesn't count. Such a scenario, it isn't ever going to see an ampere of current, but it may still be required for other ancillary purposes.

Neutral can count if the loads are extremely non-linear, in which case harmonic distortion is improtant to consider. In such a case, the neutral may even need to be larger than the phase conductors.


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## papaotis (Jun 8, 2013)

ibet your an e. engineer. i got most of that ,but would you please explain the last two sentences, as in case scenario?


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## Carultch (May 14, 2013)

To be honest, I don't work with many loads that have harmonics to worry about. I've never had to learn to size a super neutral.

I believe it is the third harmonic that is troublesome. It is at 180 Hz, and if you have it originating on all three phases, it adds up in the neutral, rather than cancels.


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