Service Size And Continuous Loads

[wwhitney]

For instance, leaving the issues raised in the OP behind, if I were to ask what is the minimum feeder capacity for a 100A continuous load . . . I would imagine you could provide an answer.

Agreed, I would answer 125A based on 215.2(A)(1)(a). There's no scoping limitation in the question, so all of the NEC is fair game.

Now if the question is "what is the minimum feeder capacity for the load calculated in accordance with Part III, IV, or V of Article 220?" followed by a list of loads which add up to 100A after relevant demand factors, I would say 100A, without inquiring about continuous vs non-continuous. Because the scoping restriction in the question limits us to Article 220, which never uses the phrase "continuous load" and has no 125% factors.

Cheers,
Wayne

P.S. Tangent: I think the NEC would be clearer if it deleted the sections on sizing conductors based on 125% of continuous loads (or replaced them with fine print notes). It is enough to have the sections on OCPD stating that except for 100%-rated OCPD, they must be sized based on 125% of the continuous load served. The 240.4 requirement that conductors be protected not exceeding their ampacity (with some exceptions) would still cause the conductors to be sized based on 125% of continuous loads. But the reason for the requirement, namely the limitations of OCPD, would be clearer.

One notable small consequence of this change would be that a 48A continuous load (e.g. an EVSE) could be wired with #6 NM cable (limited to 60C ampacity of 55A) on a 60A OCPD (using the next size up rule, 240.4(B)). As far as I can see, that would be a reasonable optimization and poses no safety issue. [And if I'm mistaken on that last point, then I would like to know, and would withdraw this suggestion.]

 

[tortuga]

A lot of things are undefined in the NEC, including 'feeder capacity'. Perhaps because the authors think that the term has a plain meaning that doesn't require a special definition.

OK then I agree with you 408.30 'feeder capacity' means ampacity or rating of the feeder or service.
Looking at the NFPA rop on when they modified it in 2010:

_______________________________________________________________
9-152 Log #1703 NEC-P09
Final Action: Accept
(408.30)
_______________________________________________________________
Submitter: Mike Theisen, St. Cloud, MN
Recommendation: Revise the text of 408.30 as follows:
408.30 General. All panelboards shall have a rating not less than the
minimum feeder capacity required for the load calculated in accordance with
Parts II, III, IV, or V of Article 220 as applicable.
Substantiation: By deleting Part II from the list of Article 220 sections
referenced in 408.30, this revision will clarify that the rating in question is the
feeder or service, not a branch circuit. Part II is referenced in Part III of Article
220, so no requirements are lost.
Panel Meeting Action: Accept
Number Eligible to Vote: 12
Ballot Results: Affirmative: 12
_______________________________________________________________

 

[david luchini]

Looking at the NFPA rop on when they modified it in 2010:

Nice find.

 

[Fred B]

OK then I agree with you 408.30 'feeder capacity' means ampacity or rating of the feeder or service.
Looking at the NFPA rop on when they modified it in 2010:

How can someone get access to the ROP for any particular code?

 

[kwired]

How can someone get access to the ROP for any particular code?

NFPA website particularly this page for NFPA 70. You will need to register with a username and password.

You can view current an many prior editions no charge, limited browsing tools and can't copy/paste content either like you can with paid elecronic versions.

Below the TIA's and errata is first and second draft information links - that is where you want to look. Older code they called them ROP's, but since they changed "proposals" to "public inputs" they did things differently. Older codes is just a PDF file with complete report of all the proposals.

Newer codes (I think 2014 and newer) is more of a interactive view of the drafted code content, Find a section you have interest in that has had changes (or even rejected PI's) and there will be a link to view the PI and committee statements and actions related to whatever section you are at.

 

[tortuga]

Kwired beat me to it yeah what he said ^^^

As to 408.30, I still disagree that the phrase "feeder capacity required for the load calculated in accordance with Part III, IV, or V of Article 220, as applicable" means we are referred to the requirements of 215.2(A)(1)(a). Both feeder and capacity and terms used in Parts III, IV, and V of 220, and "feeder capacity" is not an Article 100 defined term. So I see no reason to look farther than Parts III, IV, or V of Article 220, and nothing there refers to 125% or refers us to Article 215.
Cheers, Wayne

Yes 'feeder capacity' is a old school generic electrical term.
On this point the noun 'Capacity' used after Feeder changes the meaning of 'Feeder' from the NEC definition to a noun phrase meaning 'ampacity'.
I think a grade school sentence diagram is needed for code sentences like this.
I think we all agree on this point, David?

Final thought on this is there would be a might good case for a code change, as it's only logical to use the same noun to convey the same meaning throughout the code;
The NEC style manual 3.2.5 Special Terms says:

3.2.5.1 Ampacity. The term ampacity, as defined in Article 100,
applies to the current-carrying capacity of conductors only. Therefore,
this term shall be used in this sense, but only in this sense.