08 NEC SE ampacity

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raider1

Senior Member
Staff member
Location
Logan, Utah
Here is the ROP for the deletion of "Except 334.80" in 338.10(B)(4)(a).

7-88 Log #2639 NEC-P07 Final Action: Accept
(338.10(B)(4)(a))
____________________________________________________________
Submitter: James M. Daly, General Cable
Recommendation: Delete the phrase ?excluding 334.80? and change the
comma after ?Article 334? to a period.
Substantiation: When Type SE conductors are used for interior wiring, as a
replacement for Type NM cable, the ampacity of the conductors should be the
same as permitted for NM cable since the insulations used are the same both
NM and SE conductors.
Panel Meeting Action: Accept
Panel Statement: This action will modify the action taken on Proposal 7-84.
Number Eligible to Vote: 14
Ballot Results: Affirmative: 14

As you can see it was a proposal that was accepted by the code making panel.

Chris
 

pete m.

Senior Member
Location
Ohio
FWIW here is the verbiage accepted in the ROP's for the 2011 NEC.


7-133 Log #451 NEC-P07 Final Action: Accept in Principle
(338.10(B)(4))
_______________________________________________________________
TCC Action: It was the action of the Technical Correlating Committee that
further consideration be given to the comments expressed in the voting.
This action will be considered by the panel as a public comment.
Submitter: Richard W. Likes, L & F Electric
Recommendation: Add new text to read as follows:
Type SE service-entrance cable used for interior wiring shall comply with the
installation requirements of Part II of Article 334, excluding 334.80.
Substantiation: SE cable has always had this exception. If the manufactures
have changed the insulation on the wire, it should reflect on the temperature/
ampacity chart. This is just raising the cost of wire by having to use a larger
size. Has the NEC been wrong for all these years?
Panel Meeting Action: Accept in Principle
Accept inserted text. plus Insert language: ?Where installed in thermal
insulation, the ampacity shall be in accordance with the 60?C (140?F)
conductor temperature rating. The 90?C (194?F) rating shall be permitted to be
used for ampacity adjustment and correction purposes, provided the final
derated ampacity does not exceed that for a 60?C (140?F) rated conductor.?
Panel Statement: The panel recognizes that SE cable is listed to 75C. The
panel also recognizes that installation in thermal insulation can decrease the
ampacity of a cable assembly.
Number Eligible to Vote: 14
Ballot Results: Affirmative: 10 Negative: 4
 

raider1

Senior Member
Staff member
Location
Logan, Utah
Pete,

Thanks for posting the 2011 ROP on this.

Notice that if the SER cable is installed in thermal insulation then you are still going to be required to use the 60 degree column of Table 310.16 for the ampacity of the conductors.

Chris
 

pete m.

Senior Member
Location
Ohio
Not a problem Chris. Here's another "little nugget". It's the response I received from NFPA when I asked for a formal interpretation on this matter. If you can make sense of the answer please enlighten me:)

Date: 5/8/09

This replies to your E-mail of requesting information on NFPA 70, National Electrical Code ?, 2008 Edition or NFPA 70 ?.



A revision to the 2008 NEC resulted in a new provision in Section 338.10(B)(4) that required application of the ampacity rule for Type NM cable in Section 334.80 to Type SE cable where it is used as an interior branch circuit or feeder. This provision limited the final load ampacity of the conductor within an SE cable to the 60?C ampacity column. When contrasted to the allowance of Table 310.15(B) (6), this 2008 revision results in larger conductor sizes than would have been required by previous editions of the NEC.

The substantiation supporting these accepted proposals (7-88 and 7-90) cited temperature concerns associated with using Type SE cable as an interior wiring method. Proposal 7-90 cited a 1987 NEMA study in which the effect of embedding a cable in thermal insulation was deleterious to conductor insulation unless the conductor?s ampacity was reduced. There was no data included in either of these proposals indicating that application of Section 310.15(B)(6) to Type SE cable installed as a service or feeder wiring method, in which the conditions of use specified in Table 310.16 were not exceeded, resulted in the cable operating at temperatures exceeding its insulation temperature rating.

This brings us back to the premise of my original response and the decision that has to be made by the AHJ for feeders that ?supply all loads that are part of or associated with the dwelling unit?. One approach would be to use the Type NM cable ampacity requirement, that is now tied to Type SE cable by the revision to Section 338.10(B)(4), for all interior feeder and branch circuit installations without considering the installation conditions. Alternatively, the AHJ could use Section 90.4 and assess the particular installation and make the decision that the conditions of installation are such that application of the ampere ratings specified in Table 310.15(B)(6) does not result in the feeder conductors being exposed to operating temperatures that exceeds the conductor?s insulation temperature rating. If that is the case, the goal of the performance requirement specified by Section 310.10 can be met and the overall safety objective to maintain the integrity of the conductor insulation, by judiciously applying the ampacity and operating temperature requirements that have been cited in this response, can be achieved.

To summarize this, Section 310.10 is the performance requirement that the prescriptive ampacity rules and tables in Articles 310 and 338 are used to satisfy. Because there are some questions related to the revision of 338.10(B) (4) and how that correlates with Section 310.15(B) (6), the use of Section 310.10 can be used as the controlling requirement. Granted, that may not be as cut and dry as what you were hoping to learn, but it does provide a means by which to make a prudent determination that helps ensure conductor insulation integrity. Additionally, the 2011 NEC revision process is underway and the Report on Proposals will be available at the NFPA website around the middle of June. I know that there have been proposals directed to CMP-6 and CMP-7 on Sections 310.15(B) (6) and 338.10(B) (4). I urge you to review these proposals and submit any comments you deem appropriate so that the CMPs have the benefit of your expertise and field experience. The strength of the NEC is the process by which it is developed and you have an opportunity to help make the Code stronger.







Paul Choiniere

NFPA Senior Electrical Specialist





Important notice! This correspondence is not a Formal Interpretation issued pursuant to NFPA Regulations. Any opinion expressed is the personal opinion of the author, and does not necessarily represent the official position of the NFPA or its Technical Committees. In addition, this correspondence is neither intended, nor should be relied upon, to provide professional consultation or services.
 

M. D.

Senior Member
I think the NEC should follow the Massachusetts electric code ,..

334.80. Delete the second paragraph and revise the first paragraph to read as follows:

334.80 Ampacity. Type NM, NMC, and NMS cable shall have conductors rated at 90/C (194/F).
Where installed in thermal insulation, the ampacity of conductors shall be that of 60/C (140/F)
conductors. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be
determined in accordance with 392.11.

338.10(B)(4)(a). Identify the existing fine print note as FPN No. 1, and add a second fine print note as
follows:

FPN No. 2: This section includes service entrance cables with a round configuration commonly
known as SER cable. The interior installation of this cable is governed by the same rules as apply
to nonmetallic sheathed cable.
 
I forgot to mention that I was a little perplexed to the fact that this change is not mentioned in Mikes 08 changes course, but thanks for the ROPS; I was going to go there next, and it was very helpful in making a decision of how to handle this change.
Thanks again. Yours for a safe electrical installation, Dave E.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
what conclusion did you reach after reading the NFPA letter ?
 
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