Line/Switch leg in EMT

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User Name said:
Code defines Neutral conductor as "the conductor connected to the neutral point of a system that is intended to carry current under normal conditions." So not sure how the code is says its a CCC and yet says we don't have to count it as a CCC.
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When it only carries imbalance current, such as the neutral of a center-tapped 1ph or of a 3ph wye, it is considered to not contribute heat, because any current it carries is current not being carried by one or more line conductors.
 
If you have a MWBC the neutral may or may not count as a CCC for derating purposes. In a 2-wire circuit both conductors are CCC's.
 
OK so if I'm getting this right, a 3 wire or 4 wire system that's considering the neutral as carrying imbalanced load. So then if I move into a simple 2 wire 20 amp branch circuit, thats considered a balanced load on the neutral. And then would require counting as a CCC.
 
User Name said:
So then if I move into a simple 2 wire 20 amp branch circuit, thats considered a balanced load on the neutral. And then would require counting as a CCC.
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No, a two-wire circuit is merely two conductors carrying the same total load, so they both must count.

By balanced, we mean that all line conductors are equally loaded, so the neutral has no load to carry.
 
LarryFine said:
No, a two-wire circuit is merely two conductors carrying the same total load, so they both must count.

By balanced, we mean that all line conductors are equally loaded, so the neutral has no load to carry.
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OK cool thank you for the clarification.
 
User Name said:
I guess I could see your point there on the service feeders that could be handy.

Should note my install has no occ sensors or such, but I do get what you're saying.
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Also must consider that in recent editions the grounded conductor is required to be run or at least capable of being run in the future should a device requiring it be installed. IMO this is design issue but code made it mandatory anyway.
 
User Name said:
At first I thought wait neutrals are ccc so you got to count them...but I looked it up and sure enough 310.15(E)(1) A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted.... Thats a new one to me lol.

I would say though that a neutral IS a ccc you're just not required to count it. Personally I think it would still be a good idea to count it as one, nothing wrong with having a little extra room when sizing a pipe run right? Unless you're bidding something kind of close....
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Forget the NEC definition, here are some examples of how the Grounded conductor works.

1711296488893.png
The grounded conductor is counted as a CCC in two wire circuits

1711296588630.png
The Grounded conductor is not counted as a CCC in a MWBC when only carrying the unbalanced neutral current.

1711296681651.png

The Grounded conductor is not counted in a MWBC where the other legs carry equal current.
 

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Just in case this helps any, and at the risk of tooting my own horn
toot1.gif
:

Understanding the Neutral Conductor

Dennis, here's a really basic lesson, and we'll start with direct current, because the fact that we use alternating current is not relevant to the basics: Picture a battery, like you'd find two of in a flashlight. You have a terminal at each end, with a difference in potential of 1.5 volts...
forums.mikeholt.com
 
LarryFine said:
Just in case this helps any, and at the risk of tooting my own horn
toot1.gif
:

Understanding the Neutral Conductor

Dennis, here's a really basic lesson, and we'll start with direct current, because the fact that we use alternating current is not relevant to the basics: Picture a battery, like you'd find two of in a flashlight. You have a terminal at each end, with a difference in potential of 1.5 volts...
forums.mikeholt.com
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Hey thanks for that. Helped me understand the physics of this.
 
roger said:
Forget the NEC definition, here are some examples of how the Grounded conductor works.

View attachment 2570685
The grounded conductor is counted as a CCC in two wire circuits

View attachment 2570686
The Grounded conductor is not counted as a CCC in a MWBC when only carrying the unbalanced neutral current.

View attachment 2570687

The Grounded conductor is not counted in a MWBC where the other legs carry equal current.
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Thanks for that too that helps alot.

So my next question. So I've got an imbalanced load like that of the second picture, 20 amps on one leg, 10 on the other, and 10 returning on neutral. So there's still current flowing on the neutral, why not count it as a CCC? Is it because the circuit has the capacity of 20 amps on both legs and thus would return 0 to neutral?
 
Actually I think I'm getting this wrapped around my head now. With a MWBC you'll only have 2 ccc worth of power flowing, it's just split up over 3 wires. Do you guys run alot of mwbc for this reason? I always figured it was more of a risk of overloading the neutral. Going to have to hook some stuff up in my shop and test this lol.
 
User Name said:
With a MWBC you'll only have 2 ccc worth of power flowing, it's just split up over 3 wires.
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Miyagi have hope for you! ;)

Do you guys run alot of mwbc for this reason?
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Moreso before the rule changes, yes. Also, fewer wires and less overall voltage drop.

Going to have to hook some stuff up in my shop and test this lol.
Excellent idea.
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Think of it like this: Just as each line conductor carries as much current as it can in its attempts to keep the load end at the same voltage as the source end (i.e., minimizing voltage drop), so does the shared neutral carry as much current as it can in its attempt to keep the load end at zero volts.

I always figured it was more of a risk of overloading the neutral.
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If you were to connect more than on line conductor to any given phase, the current on the shared neutral would be additive, and could indeed overload it. As long as the lines are distributed among the source phases, the neutral current would be subtractive, and only be made of the difference.
 
LarryFine said:
If you were to connect more than on line conductor to any given phase, the current on the shared neutral would be additive, and could indeed overload it. As long as the lines are distributed among the source phases, the neutral current would be subtractive, and only be the difdifference
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I was thinking this, if you hooked the 2 circuits on the same phase you'd be adding to the neutral, gotta be on the seperate phases. Code requires the two circuits to be disconnected together, so they end up on a double pole breaker anyway solving that issue.
 
User Name said:
I was thinking this, if you hooked the 2 circuits on the same phase you'd be adding to the neutral, gotta be on the seperate phases. Code requires the two circuits to be disconnected together, so they end up on a double pole breaker anyway solving that issue.
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1711303894287.png
 
Not going to lie, my mind is blown lol. All I had to do to see this in action is clamp on the neutral of my shop panel and turn some stuff on opposite phases on/off. With two circuits on neutral load was 3.6 amps. With 1 off 3.70, and with the other off 5.16. The amerage went UP with things turned off. I feel like this is something I should have known by now 🤔.
 
Keep in mind the neutral would only be net zero with split wire single phase and on wye systems where all ungrounded conductor currents are equal.

With two ungrounded conductors and the neutral of a wye system that neutral carries approximately same amount of current as the ungrounded when they are equal, and is considered a CCC for ampacity adjustment reasons in that situation.
 
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