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#197123 - 11/10/10 04:11 AM 210.19 exc#2  
Niko  Offline
Member
Joined: Aug 2006
Posts: 356
Campbell, CA
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







Be kind to your neighbor, he knows where you live


2017 / 2014 NEC & Related Books and Study Guides

#197125 - 11/10/10 09:53 AM Re: 210.19 exc#2 [Re: Niko]  
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
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
_________________________________


Don(resqcapt19)

#197128 - 11/10/10 01:25 PM Re: 210.19 exc#2 [Re: resqcapt19]  
Niko  Offline
Member
Joined: Aug 2006
Posts: 356
Campbell, CA
Thanks Don,


Be kind to your neighbor, he knows where you live


#197130 - 11/10/10 02:54 PM Re: 210.19 exc#2 [Re: Niko]  
KJay  Offline
Member
Joined: Nov 2007
Posts: 763
MA, USA
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.


#197134 - 11/10/10 05:43 PM Re: 210.19 exc#2 [Re: KJay]  
LarryC  Offline
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US
Originally Posted by KJay
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.


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.


#197136 - 11/10/10 06:16 PM Re: 210.19 exc#2 [Re: LarryC]  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
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?

Last edited by renosteinke; 11/10/10 06:16 PM.

#197137 - 11/10/10 09:33 PM Re: 210.19 exc#2 [Re: renosteinke]  
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
John,
I would agree that a 20 amp OCPD would require a grounded conductor with an ampacity of 20 amps or more.


Don(resqcapt19)

#197141 - 11/11/10 12:53 PM Re: 210.19 exc#2 [Re: resqcapt19]  
KJay  Offline
Member
Joined: Nov 2007
Posts: 763
MA, USA
Originally Posted by resqcapt19
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.



#197142 - 11/11/10 02:48 PM Re: 210.19 exc#2 [Re: renosteinke]  
KJay  Offline
Member
Joined: Nov 2007
Posts: 763
MA, USA
Originally Posted by renosteinke
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?


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.


#197144 - 11/11/10 09:15 PM Re: 210.19 exc#2 [Re: KJay]  
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
KJay,
How does 240.4(D) not apply?


Don(resqcapt19)

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