210.19 Exception No. 2: Permits grounded conductors not connected to an overcurrent device to be sized at 100 percent of the continuous and noncontinuous load.

A hypothetical question:

19A continuous load:
ungrounded THHN 19x125% = 23.75A requires a #10 AWG
grounded THHN 19x100% = 19A requires #12 AWG

In a two wire circuit the ungrounded and the grounded have the same current flow. How come the Neutral can be smaller than the grounded?

Is it because the OCPD is rated at 80% ??
Is it because the #12 ampacity is 35Amps so it is within capacity?

Thanks

2-166 Log #1319 NEC-P02 Final Action: Accept in Principle
(210.19(A)(1))
____________________________________________________________
TCC Action: The Technical Correlating Committee understands that the Panel Action on this Proposal is to identify the existing Exception as “Exception No. 1” and the Exception being added as “Exception No. 2” to be located immediately following the existing Exception.

Submitter: Mike Holt, Mike Holt Enterprises

Recommendation: Revise as follows:

210.19 Conductors – Minimum Ampacity and Size.
(A) Branch Circuits Not More Than 600 Volts.
(1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch-circuit conductor size, Branch-circuit conductors that are connected to an overcurrent device assembly shall have a minimum allowable ampacity, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

Substantiation:

“Minimum Rating and Size”: The identical wording should be used for 210.19, 215.2, and 230.42. Confusion reigns as to under what conditions grounded conductors are subject to the same 125 percent of continuous load sizing requirements as are ungrounded conductors. During the 2005 Code cycle this issue was addressed for feeders, but action was deferred. ROC No. 2-145 included a lucid, sound “substantiation” that unfortunately was rejected by CMP 2 at that time. Now is an excellent time to re-evaluate that “substantiation” and adopt its intent.

The basis for the 125 percent requirement stems from the manner in which listed overcurrent devices are tested. During continuous load tests of enclosed overcurrent devices, in order to prevent nuisance tripping, it has been found that it is necessary to limit the current to 80 percent of the device’s rating. Conductors are sized, then, (1) at 125 percent of the continuous current in accordance with the allowable ampacity determined from Table 310.16, and (2) per the terminal temperature limitations of 110.14(C).

The reality is that the enclosed overcurrent devices rely on the mass of the conductors to act as heat sinks that dissipate excess thermal energy and thereby avoid unacceptable nuisance tripping. Of course, since overcurrent devices cannot distinguish between ungrounded and grounded conductors, in both cases the conductor sizes must be based on calculations that include an additional 25 percent factor when the load is continuous. On the other hand, there is no reason to add 25 percent to the load of a conductor that is not connected to a device that is not subject to nuisance tripping, such as in the case of a grounded conductor connected a neutral terminal bus.

The end result of this proposal is twofold:
1. The additional 25 percent continuous load requirement applies only to conductors, both ungrounded and grounded, that connect to an overcurrent device (unless, of course, the assembly is listed for operation at 100 percent of
its rating).
2. Grounded conductors that carry continuous loads and that connect only to neutral buses, or to devices not subject to nuisance tripping, are not required to have their loads increased by 25 percent.

This proposal accomplishes that goal and, in hand with similar proposals made in two other Articles, brings into conformity the requirements for branch circuits (210.19), feeders (215.2), and services (230.42).

Panel Meeting Action: Accept in Principle

Add a new exception to 210.19(A)(1) to read:
Exception: Grounded conductors that are not connected to an overcurrent device shall be permitted to be sized at 100% of the continuous and noncontinuous load.

Panel Statement: The panel has accepted the submitter’s concept, but has added the provision as an exception to the main rule. The concern with the submitter’s proposed language is that it may be interpreted that the conductors
have to terminate directly to an overcurrent device.
Number Eligible to Vote: 12
Ballot Results: Affirmative: 12
_________________________________

Thanks Don,

Just to expand on this a little more, for other than possibly a service or feeder application, is there anything that actually prevents manufactures from producing NM-B cables with reduced "neutrals" for use in branch circuits?
Such as, #12 with a #14 neutral conductor or #10 with a # 12 neutral, etc.
I seem to remember seeing some NM cables being made this way many years ago.

I can see this not being a good idea and thought there was something that required them to be the same size as the ungrounded conductors up to a certain size, but so far, I haven’t been able to find anything in the NEC or White book that indicates this.

The only things I could see would be:
1) New tooling
2) New safety approvals
3) New packaging
4) New catalogs
5) New manufacturing BOMs
6) New literature to explain when one could and could not use the new material
7) More returns
8) More confusion

But aside from that, no I don't think there is any physically preventing manufacturers from producing this product.

I thought the NEC did not allow us to reduce the neutral on the smaller (15, 20, 30-amp) circuits? Or, am I confusing the ground with the neutral here?

John,
I would agree that a 20 amp OCPD would require a grounded conductor with an ampacity of 20 amps or more.

I would also agree, and I don’t think it will ever be an issue again with NM cables, but I’m wondering if this is why the values for #12 and #14 at 60-degree C were changed in the 2011 NEC.

Otherwise, it seems that since the grounded conductor is not connected to an overcurrent device, it would only have to sized at 100% and 240.4[D] wouldn’t seem to apply. Currently, #14 is rated at 20A at 60-Degree C in Table 310.16 of 2008 NEC.

I do see where 240.23 states that a change in the grounded conductor shall be permitted when a change occurs in the ungrounded conductors are changed, but it doesn’t appear to be required and the change could mean smaller or larger.

This is what I’ve always thought as well. I believe we were even taught this in class many years ago. This thread has got me wondering though, since I also don’t see what would prevent someone from pulling a #12 THHN and a #14 THHN in a raceway, then terminating them on a device or equipment with 60 or 75-degree C lugs and proclaiming it as a 20A/120V circuit.
If I had seen someone doing this on a job, I would have said that it’s not allowed, but now I can’t actually find where it would be prohibited.

KJay,
How does 240.4(D) not apply?

To be honest, I’m not sure that it doesn’t.
I may be over thinking this, but what I see is that 310.16 is allowable conductor ampacity and 240.4[D] is overcurent protection. Two different things, IMO anyway.

Yes they are two different things and that is a fact that is often missed. This is a very important issue when applying the provisions of 240.4(B). You just have to remember that 240.4(B) does not change the ampacity of the conductor...it just permits the use of an over sized OCPD.

Okay, it seems clear to me again that 240.4[D] would apply as usual here. Not sure why it wasn’t registering with me regarding neutral condutors.

If you believe 240.4(D) is overload protection as opposed to short circuit protection, it clearly applies to the neutral. What goes in comes out the other end according to Mr Kirchoff.

My AHJ makes life simple: #12 is the minimum conductor permitted on all commercial construction -- to include Romex if commercial.

I agree that it also includes the neutral, but even the NEC’s own description of a branch circuit could be seen as a little vague.
Art.100 defines a branch circuit is defined as “the circuit conductors between the final overcurrent device protecting the circuit and the outlet[s].”
I think it is assumed to include a grounded [neutral] conductor, but may have been intentionaly left out since not all branch circuits use a neutral.

If the overcurrent protection rules in Article 240 apply to the neutral, how can we size the neutral based on the neutral current as permitted for feeders? The only requirement for the feeder neutral size is the larger of what is required for the load or the size of the required EGC for the circuit. This often results in a neutral that is really only protected by the design calculations, not by the ungrounded conductor OCPD.
Yes, I know that I said that the rules in 240 apply to the neutral in an earlier post, but there are issues with that when we are talking about feeder circuits.

Okay, so now I guess this indirectly seems to bring back the issue I was struggling with earlier. If we know that neutral current carrying capacity is not based directly on the rating of overcurrent protection for feeders and services, would this not also apply to all branch circuit neutral conductors as well?
Especially with regard to the situation covered in 240.4[D] for #14 conductors being used as a neutral for 20A branch circuits.

The only time you can downsize a neutral is when there is a significant amount of line to line load. That will not be the case on a 120v branch circuit. If you have a 120v branch circuit 240.4(D) applies to the neutral too in my opinion.

Greg,
I am aware that it would be a very rare case where you could downsize a branch circuit neutral, but my question was about a feeder neutral that is permitted to be downsized based on the load calculations. If the rules in Article 240 require overcurrent protection of the neutral, how can we downsize it?

You have to look at the connected load. If a significant part of the connected load is line to line only you can safely downsize the neutral but since (2005?) they say in addition to the 220.61 calculation (to provide overload protection), 250.122 will be the minimum size (to provide short circuit protection).

Greg,
If we are saying that the neutral conductor is required to be protected at or below its ampacity per the rules in 240, there is no way that we can use a "downsized" neutral for a feeder, no matter what the rules in the other code sections say.

It all depends on what you are protecting it from. If you are talking about "overload" then 310.15 rules and that is the case when you size to line to neutral loads. If you are just protecting it from a line to neutral fault that is short circuit protection and you can use 250.122.
When you think about it, we don't seem to have a problem sizing EGCs with 250.122 and that is sufficient to clear a ground fault.
I agree there was a problem when they only used 220.61 and you could end up with a very small neutral that might not clear a bolted L/N fault.

Greg,
I am talking about 240.4 which requires the conductors to be protected at their ampacity. I guess my point should be, contrary to what I said before, that Article 240 should be changed to make it clear that it only applies to ungrounded conductors. An undersized feeder neutral as permitted by the code rules is not protected per 240.4.

I agree, you have found a hole in the code. They should either add "feeder neutrals" to 240.4(G) table or remove 220.61.
I am going to bounce this off of the Fl IAEI group and see if we are missing something.

Don I am trying to defend your position over at Fla IAEI and they keep telling me 240.4 dies not apply to neutrals. I point out it doesn't say that.

http://www.iaeifl.org/forums/ubbthr..._there_a_conflict_between_22.html#UNREAD

Greg,
Maybe it shouldn't apply to neutrals, but the wording only says "conductors" must be protected. I don't know how you can have a neutral that is not a conductor.

I think that this is just one more of those cases where the code doesn't really say what the writers thought it did. I don't think Article 240 is intended to apply to neutrals, but the wording makes it apply.

Greg,
Maybe it shouldn't apply to neutrals, but the wording only says "conductors" must be protected. I don't know how you can have a neutral that is not a conductor.

I think that this is just one more of those cases where the code doesn't really say what the writers thought it did. I don't think Article 240 is intended to apply to neutrals, but the wording makes it apply.

You convinced me but I think it is just a hole in the code. I still think the neutral is protected against overload by 220.61 and against short circuit by 250.122 but 240.4 does not say that.