FAQ: When is a neutral a current carrying conductor?

[George Stolz]

b] Travelers between 3ways or 4ways are never both current carrying conductors at the same time so don't count both. . Only count the pair as one.

While I do agree with your reasoning, I do not see this accounted for in the present code language. I could see enforcability in requiring both conductors to be counted as current-carrying, despite reason.

JMO,

 

[dnem]

Pop quiz:

A 120/208 4 wire feeder from a wye source feeds a panel. The panel is fully loaded with a large heater connected from the A leg to the B leg, with 120V loads fed between the C leg and the neutral. Is the neutral a 'current carrying conductor'.?

-Jon

I like your quiz because it’s so easy to answer the wrong way.
You ask about the neutral and using the term neutral for all grounded conductors.

First
The problem with saying the neutral is that there is no such thing. . There are 2 types of grounding conductors, equipment bonding/grounding and electrode earthing/grounding, that are grounding throughout the system. . There is an ungrounded conductor that is ungrounded throughout the system. . But there’s no such thing as a neutral that is neutral throughout the system.

Neutral is a condition not a category label that applies thruout the system. . The common connection point of a wye transformer is grounded and neutral. . The conductor connected to that common point and brought to the service is grounded and neutral. . The conductor connected to that common point and feeding a subpanel is grounded and neutral. . The conductor connected to that common point and part of a multiwire HR, that has all hot conductors of the system present, is grounded and neutral. . The conductor connected to that common point and part of a HR, that does not have all hot conductors of the system present, is grounded but not neutral. . So a grounded neutral commonly enters a junction box, grouped in the same circuit run with all of the hot conductors, and be connected to other grounded conductors that are not neutrals.

An ungrounded conductor is always ungrounded throughout the whole system.
A grounding conductor [electrode or equipment] is always connected to ground throughout the whole system.
A grounded conductor is always grounded throughout the whole system.
But a neutral conductor is not always neutral throughout the whole system.
Neutral is a condition that applies to the grounded conductor is some places but not in other places.

Secondly
The problem with using the term ‘neutral’ instead of grounded. . There is current carrying and then there’s current carrying but unbalanced current only. . The code treats them differently.

Is the neutral a 'current carrying conductor'.?

Yes the neutral is always current carrying but the word ‘neutral’ means it’s also unbalanced current only. . Is the grounded conductor actually a neutral at the point you ask about in your question ? . On the 120v circuits [of a 120/208 wye] the answer is no. . The T310.15(B)(2)(a) count specifies unbalanced current only current carrying conductors [310.15(B)(4)] so that wouldn’t apply to grounded conductors in those 120v circuits.

David

 

[George Stolz]

Tricky question indeed.

I could argue that since legs A and B are never connected to the neutral, this feeder really is two separate circuits.

I would disagree. The feeder is a feeder, and would be dealt with as an individual component of the system when applying this section. The branch circuits come after, and would also be dealt with according to their own characteristics.

Now, if the feeder is supplying harmonic-inducing loads, that can be "seen" at the feeder location, and would one would still be addressing the characteristics of the feeder itself in applying 310.15(B)(4)(c). The easiest way to predict or detect this scenario is to look downstream of the feeder, at the loads, to make this determination. But with the right equipment we would not need to know what the loads were, the harmonics would be detectable for the application of 310.15(B)(4)(c).

I could also argue that the neutral does not carry only imbalance current, since if all legs are loaded the neutral is still fully loaded.

Based on this set up, I think that the code requires this grounded conductor to be counted as a current carrying conductor because it is not carrying the unbalanced load other conductors in the circuit. It is my opinion that 310.15(B)(4)(a) supports this conclusion.

I was initially on Charlie Beck's side of this argument, but as I was drafting the rebuttal to Jon and Don's statements above, I saw (what I perceived to be) my mistake and editted my first statement above.

Using the application of 310.15(B)(4)(c) as an example, we can apply 310.15(B)(4)(a) in the same fashion.

It is easier to determine the feeder neutrals function by looking at the loads, but it is not necessary, again. 310.15(B)(4)(a) is written towards how the feeder behaves with the loads connected, so it is enforceable in that way too.

Since it does not carry solely "unbalanced current" as (a) requires, it must be counted.

This goes against the grain of routine, but this isn't a routine feeder, and that's why our reflex is to say it doesn't count. But there is no circuit path for neutral current to get back to the source via other ungrounded conductors, A and B.

If the appropriate equipment is connected to this feeder in operation and we put blinders on to the loads, then the words would come alive for this feeder. Other conductors of this feeder circuit are not behaving to get rid of the current on the neutral, so (a) isn't satisfied.

That was a really good question, I know it's the first time I've ever thought of this that way.

 

[George Stolz]

David, I've read your reply twice now and I'm not sure what your answer to the question is.

To rephrase Jon's question: Is the grounded circuit conductor of the feeder described, a current-carrying-conductor in the application of 310.15(B)? :-?

 

[LarryFine]

My opinion:

The feeder is not a MWBC, it is a feeder; it supplies a panel.

The feeder's neutral does not carry only imbalance current, because of the make-up of the panel's circuits.

The feeder's neutral must be considered a CCC.

 

[dnem]

Pop quiz:

A 120/208 4 wire feeder from a wye source feeds a panel. The panel is fully loaded with a large heater connected from the A leg to the B leg, with 120V loads fed between the C leg and the neutral. Is the neutral a 'current carrying conductor'.?

-Jon

?Is the neutral a 'current carrying conductor'.??
The neutral is always a current carrying conductor in every installation.
But the better question is: . Is the grounded current carrying conductor a neutral ?

The answer to that question would change according to what portion of the system is being examined. . There are 3 separate sections of the system described in the pop quiz:
Section 1) the feeder ? ?120/208 4 wire feeder from a wye source feeds a panel?
Section 2) 240v [2 hots] heater ? ?connected from the A leg to the B leg?
Section 3) 120v loads ? ?fed between the C leg and the neutral? um?.. neutral, no we need to say ?fed between the C leg and the grounded conductor?

Section 1
Since the sentence says ?feeder?, I?ll assume that the wye source first makes a stop at the service equipment and that the 120/208 4wire specification means that the feeder EGC is metal conduit between the service and the subpanel. . If all of that is the way that I?m picturing it, then yes, the grounded current carrying conductor is a neutral [ie: unbalanced current only].

Section 2
The 240v heater may be ?straight? 240v or may require a grounded conductor for control functions. . The 240v circuit does not have all ungrounded hot conductors of the system present in the wireway in question. . So therefore, no, the grounded current carrying conductor is not a neutral.

Section 3
The 120v circuits do not have all ungrounded hot conductors of the system present in the wireways in question. . So therefore, no, the grounded current carrying conductors are not neutrals.

David

 

[dnem]

David, I've read your reply twice now and I'm not sure what your answer to the question is.

To rephrase Jon's question: Is the grounded circuit conductor of the feeder described, a current-carrying-conductor in the application of 310.15(B)? :-?

George, I just now saw your post. . Does my last post answer your question ?

 

[dnem]

My opinion:

The feeder is not a MWBC, it is a feeder; it supplies a panel.

The feeder's neutral does not carry only imbalance current, because of the make-up of the panel's circuits.

The feeder's neutral must be considered a CCC.

The feeder's grounded conductor is always a CCC. . But I read your point to be that the grounded conductor is not unbalanced current only therefore is not a neutral which means it does not get the neutral exemption from being counted by 310.15(B)(4).

If I’m reading your point correctly, I think you’re right.

If the 120v loads are all stacked on one phase, then the grounded conductor of the entire feeder is not a neutral.

I hadn’t thought about that before.

David

 

[George Stolz]

David, a neutral with harmonics could be carrying "solely the unbalanced current" and still be considered a CCC, so I'm not quite sure what benefit there is to determining whether the conductor in question is a true "neutral" in the application of this section.

 

[winnie]

I would claim that in the presence of triplen harmonics, a neutral which carries only the unbalance fundamental current is actually carrying _balance_ current with respect to the harmonics. In the presence of harmonics, the neutral does not carry _only_ unbalance currents.

I would go so far as to claim that the fact that we don't _count_ a neutral as a current carrying conductor when a minor amount of the load is non-linear is in fact an additional permission. If there is _any_ triplen harmonic, then the neutral is carrying _some_ balance current. But we don't have to count it until the non-linear load is the major portion of the total loading.

Going back to my screwy example, it is clear that in a horribly and intentionally imbalanced panel, the neutral of the feeder to that panel will be a full current carrying conductor...but any real 120/208 three phase panel will have a mixture of single pole and two pole loads, roughly distributed across the whole panel. In this case, the imbalance caused by the two pole versus single pole loads will probably be negligable, and IMHO the neutral of a feeder to such a panel is reasonably not counted as a CCC for derating.

-Jon

 

[dnem]

I had a conversation with someone over the weekend that's alot smarter and more experienced than I am. . He didn't agree with my definition of "neutral". . We read thru 310.15(B)(4) line by line. . Now I have to take back most of what I?ve said on this thread. . I think it?s called ?eating humble pie?. . I just hope the pie isn?t lemon. . I really don?t like lemon pie.

The thought of sorting thru my past statements and correcting all of them sounds less appealing than a trip to the dentist. . So I?m going to correct just one post and then give up.

First
The problem with saying the neutral is that there is no such thing. . There are 2 types of grounding conductors, equipment bonding/grounding and electrode earthing/grounding, that are grounding throughout the system. . There is an ungrounded conductor that is ungrounded throughout the system. . But there?s no such thing as a neutral that is neutral throughout the system.

?But there?s no such thing as a neutral that is neutral throughout the system.?
Yes, there is. . If it?s connected to the common point, it?s considered the neutral throughout the system. . It could be a ?neutral conductor that carries only the unbalanced current? [310.15(B)(4)(a)] in one section and then a neutral ?considered a current-carrying conductor? [310.15(B)(4)(c)] in another section of the system but it?s still considered the neutral throughout the whole system.

Neutral is a condition not a category label that applies thruout the system.

No it?s not. . I was wrong.

The grounded conductor connected to the common point is always called the neutral. . The word ?common? is the same as neutral. . I was wrong in saying that the word ?balanced? is the same as neutral. . A neutral can be either unbalanced [in which case it is considered current-carrying] or balanced [in which case it?s not considered current-carrying].

An ungrounded conductor is always ungrounded throughout the whole system.
A grounding conductor [electrode or equipment] is always connected to ground throughout the whole system.
A grounded conductor is always grounded throughout the whole system.
But a neutral conductor is not always neutral throughout the whole system.
Neutral is a condition that applies to the grounded conductor is some places but not in other places.

Unbalanced is the condition that applies to the grounded conductor is some places but not in other places. . The label neutral applies throughout, in the current carrying grounded conductor sections and the unbalanced current grounded conductor sections.

Yes the neutral is always current carrying but the word ?neutral? means it?s also unbalanced current only.

No it?s not. . I was wrong.

The neutral is always a current carrying conductor in every installation.

No it?s not. . I was wrong. . [Is there an echo in here ?]
310.15(B)(4) doesn?t use the term ?current carrying conductor? [310.15(B)(4)(c)] for the neutral in the system sections where the neutral only carries ?unbalanced current? [310.15(B)(4)(a)].

Now that I completed my confession I wish to ask for forgiveness and promise not to argue with anyone ever again ?.. well, ?.. no arguing for the rest of the day, is that good enough ?

David

 

[dnem]

b] Travelers between 3ways or 4ways are never both current carrying conductors at the same time so don't count both. . Only count the pair as one.

While I do agree with your reasoning, I do not see this accounted for in the present code language. I could see enforcability in requiring both conductors to be counted as current-carrying, despite reason.

JMO,

I have to find a way of disagreeing with you without arguing because I’ve promised not to argue for the rest of the day.

I’m going to say that 220.82(C) and 422.12X2 set a precedent in considering that some loads and some wiring are never energized at the same time and that can be taken into consideration and adjustments can be made accordingly. . A reasonable person would come to a reasonable conclusion while a legalistic person would come to a legalistic, unrealistic, and unreasonable insistence on hanging on a precise word.

But I mean that in a completely dispassionate calm and non-argumentive way. . You can tell because I stuck a smiley at the end of the sentence.:wink:

David

 

[winnie]

How about one slice of lemon pie, one slice of pecan pie, and say 10 ' The difference between NEC language and American Language is about as large as the difference between the language of America and England.'

Frankly I like your use of Neutral better than the NEC usage, and I'd abolish the use of Neutral if at all possible, especially in 310.15(B)(4)

We have the 'grounded conductor', which is electrically connected to Earth, and bonded to all non-current carrying metal.

We have the 'common conductor', which is derived from a supply terminal with a voltage that is the vector '0' of at least two other supply terminals in the system. The common supply terminal is often, but not always, at the voltage vector '0' of the entire system.

We have the 'conductor which carries only unbalanced current', which is part of a multiwire circuit in which the other conductors of the circuit are connected to _all_ of the supply terminals for which the common is the vector zero, and a bunch of other factors which I can argue about but which I still don't have good words for, eg. balanced circuit design, equal sizing, lack of harmonics, etc. (Note: requirements here that exceed 310.15(B)(4)

We have the 'conductor named by 310.15(B)(4)', which is similar to the 'conductor which carries only unbalanced current', except for exceptional cases intended to be confusing

-Jon

 

[dnem]

How about one slice of lemon pie, one slice of pecan pie, and say 10 ' The difference between NEC language and American Language is about as large as the difference between the language of America and England.'

It'a a deal !

I'll eat the pecan pie while I'm secretly sliding the lemon pie under the table to the dog.

Frankly I like your use of Neutral better than the NEC usage, and I'd abolish the use of Neutral if at all possible, especially in 310.15(B)(4)

Thank You, you're being very kind to me during my shame

We have the 'conductor named by 310.15(B)(4)', which is similar to the 'conductor which carries only unbalanced current', except for exceptional cases intended to be confusing

-Jon

"except for exceptional cases intended to be confusing"

Yeah, that's quite good !

I really like how those words all flow together and the meaning is so true !
I just wonder what members of CMP6 would think of the word "intended".

David

 

[benaround]

I say we add 1 recpt. to 'A' phase and 1 recpt. to 'B' phase and start it

all over agian.