2023 NEC Section 310.12 and Sub-Panels

by | Jul 9, 2024 | NEC Code, NEC Section 310.12, Sub-Panels

I was recently asked the question:

“Can 2023 NEC Section 310.12 and the corresponding table be used for sub-panels in a dwelling?”

Sub-Panel. Rocky Mountain Chapter of the IAEI.This question prompted the following blog, highlighting the most common violation in my experience, associated with Section 310.12.  The remainder of this blog is my answer to the question, hope you enjoy.

Can Section 310.12 be used?  Hmmm, I would say maybe, this section has some conditions, the one most often violated being the feeder or service conductors supplying the dwelling, supply all loads associated with the dwelling.  Section 310.12 permits feeder and service conductors to be sized in accordance with sub-divisions (A) through (D), in short (A) and (B) require the conductors supply “the entire load associated with a one-family dwelling, or the entire load associated with an individual dwelling unit in a two-family or multifamily dwelling”.

Example of a common misapplication would be a sub-panel supplying only the loads associated with a garage.  First off, a garage is not a dwelling, secondly, if the sub-panel only supplies some, but not all loads associated with the dwelling, 310.12 cannot be applied.

It is important to remember 310.12 does not give exception to conductors having an ampacity at least equal to, or greater than the calculated load.  Lastly, it needs to be mentioned 2023 NEC Section 240.4(B) may permit conductors to be protected by an OCPD of the same ampere rating as that of Table 310.12.

For example, where a 4/0 AWG aluminum feeder supplies a basement sub-panel, if the sub-panel does not supply all the loads associated with the dwelling, 310.12 is not applicable, however, the ampacity of a 4/0 does not correspond with the ampere ratings of a standard OCPD, and 240.4(B) permits the next higher standard size to be used.  In this example it is Section 240.4(B) that permits a 200-ampere OCPD to protect the 4/0 aluminum conductors and not Section 310.12.

Author
Chris Papp

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NEC Changes and Adoption

by | Sep 7, 2022 | NEC Code

NEC Changes and Adoption

Did you know…

NEC Changes and Adoption

​It is approaching that time again, bikini season, whoops…. Wrong article, NFPA 70 Public Input Stage.  Most, if not all of us in the electrical industry are well aware the NEC is revised, then updated every three years for the latest version.  This blog will not go into any further discussion of government adoption, but the link below to the NFPA website provides a map of NEC State adoption, color coded by the code cycle year adopted.

http://www.nfpa.org/NEC/NEC-adoption-and-use/NEC-adoption-maps

NEC Standards Development Process

The NEC process can be broken down into four steps.  It all begins with the issuance of a public notice that the NEC revision process has begun, this is usually within a few days of a newly released edition of the NEC.  Fun time, if you are involved in the electrical industry, you or somebody you know have at some point discussed how a particular Section of the NEC could be or have been improved by the code making panel (CMP).  Reality is anybody in the electrical industry can have a significant impact on the NEC, it is truly a consensus standard.

After issuance of public notice that the NEC revision process has begun anybody can submit a public input on NFPA’s website.  Public inputs are most often submitted by interested parties such as the IAEI but can be submitted by any individual as well.

The Public Input or PI

Public inputs will require identification of the submitter, and the organization or company affiliation of the submitter.  The submitter can also simply be unaffiliated with any company or organization, just a NEC geek wanting to be heard.  PI’s must identify the specific Code Section of the proposed revision.  Next the PI will need a statement of the problem and substantiation for why the change is necessary.  All that’s left now is the proposed wording of the revised text or the wording to be deleted.

In conclusion I leave all with the infamous words of Keith Loftland that would be spoken several times during any of the many educational seminars he had instructed for IAEI.  “I look forward to your public input”.

Author
Chris Papp

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