2008's 310.15(B)(6) "100% Rule" Eliminated

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George Stolz

George Stolz

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Looks like, for now, the rule stating that a conductor must serve 100% of the dwelling unit's load to use Table 310.15(B)(6) is going away:

6-88 Log #3064 NEC-P06 Final Action: Accept in Principle
(310.15(B)(6))
_______________________________________________________________
Submitter: Mike Holt, Leesburg, FL
Recommendation: Revise text as follows:
(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. For individual dwelling units of one-family, two-family, and multifamily dwellings, conductors, as listed in Table 310.15(B)(6), shall be permitted as 120/240-volt, 3-wire, single-phase service-entrance conductors, service-lateral conductors, and feeder conductors that serve as the main power feeder(s) to each dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard(s) that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit. The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.61, and 230.42 are met.

Substantiation: This proposal changes this section back to the 2005 code language. Requiring the feeder to serve the entire load in order to use this section simply does not make sense. For example, consider a 200A service for a dwelling. If the installation consists of a single 200A breaker, 200A feeder and 200A panel, the user can use this section. If the air conditioners for this house are removed from the 200A panel and put outside at the service equipment, there is now less load on the feeder conductors, yet the according to the 2008 revision to this rule, I must now make the conductors larger to serve a smaller load! Obviously this doesn’t make sense.
Panel Meeting Action: Accept in Principle
Panel Statement: See panel action on Proposal 6-83a.
Number Eligible to Vote: 11
Ballot Results: Affirmative: 11
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Didn't think I could find more reason to admire Mike Holt than I already do, but this is in my humble little opinion, a great reason to do so. Thank you Mr. Holt for bringing this up and providing common sense reason to the issue.
 
macmikeman said:
Didn't think I could find more reason to admire Mike Holt than I already do, but this is in my humble little opinion, a great reason to do so. Thank you Mr. Holt for bringing this up and providing common sense reason to the issue.
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Even though accepted in principle, the current draft is somewhat different...

310.15(7) 120/240-Volt, Single-Phase Dwelling Services and
Feeders [ROP 6-53].
(a) For individual dwelling units of one-family, twofamily,
and multifamily dwellings, conductors, as listed in
Table 310.15(B)(7), shall be permitted as 120/240-volt,
single-phase service-entrance conductors and servicelateral
conductors. [ROP 6-53]
(b) Feeder conductors for a dwelling unit, after adjustments
and corrections, shall not be required to have an
ampacity rating greater than the Table 310.15(B)(16) allowable
ampacity of the service conductors. [ROP 6-83a, 6-85]
(c) The grounded conductor shall be permitted to be
smaller than the ungrounded conductors, provided the requirements
of 215.2, 220.61, and 230.42 are met.
Click to expand...
Note Table 310.15(B)(7) is the same as is currently 310.15(B)(6).

I'm not quite sure how to interpret the proposed change. Say for instance when Type SE cable is used for SE conductors. SE is not even listed as a conductor type in Table 310.15(B)(16). One good thing is the draft excludes 334.80 from the interior installation requirements, so we can use the 75?C column for termination rating, and perhaps the 90?C column for adjustments (even though SE is not among the named types :-? ).
 
Smart $ said:
Even though accepted in principle, the current draft is somewhat different...


Note Table 310.15(B)(7) is the same as is currently 310.15(B)(6).

I'm not quite sure how to interpret the proposed change. Say for instance when Type SE cable is used for SE conductors. SE is not even listed as a conductor type in Table 310.15(B)(16). One good thing is the draft excludes 334.80 from the interior installation requirements, so we can use the 75?C column for termination rating, and perhaps the 90?C column for adjustments (even though SE is not among the named types :-? ).
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I'm sorry. I don't follow. 334.80 and 338.10 seem to be intact, slightly clarified, but still present.
 
Smart $ said:
SE is not even listed as a conductor type in Table 310.15(B)(16).
Click to expand...

I am confused by this statement. The 2008 does list se cable and the proposal to eliminate the conductors from the title of Table 310.15(B)(6) was rejected. What am I missing besides some brain cells. ;)

6-89 Log #3493 NEC-P06 Final Action: Reject
(Table 310.15(B)(6))
_______________________________________________________________
Submitter: Mike Theisen, Midwestern Electrical Seminars
Recommendation: Delete Type SE cable and USE from the heading of the
table in order to correlate with the 2008 NEC changes to Article 338.
Table 31015(B)(6) Conductor Types and Sizes for 120/240-Volt, 3-Wire,
Single-Phase Dwelling Services and Feeders. Conductor Types RHH, RHW,
RHW-2, THHN, THHW, THW, THW-2, THWN, THWN-2, XHHW, XHHW-2,
SE, USE, USE 2.
Substantiation: In Table 310.16, the 60 degree ?C? ampacity of Type SE
cables and USE conductors is substantially lower than the ampacities permitted
when applying Table 310.15(B)(6). Considering that interior feeders can be
routed within insulating material, just makes a bad situation worse. 338.10(B)
(4) requires interior installation of Type SE cable to comply with Part II of
Article 334, which limits the ampacity of the cable to the 60 degree ?C?
column in Table 310.16. 338.12(B)(1) prohibits USE for interior wiring and
where USE cable is installed underground they must comply with Part II of
Article 340, which limits the ampacity of the USE cable to the 60 degree ?C?
column in Table 310.16.
Panel Meeting Action: Reject
Panel Statement: Service-entrance cables are listed and designed for the types
that are proposed to be rejected. The substantiation for this proposal is incorrect
and is not justified.
SE, USE, -2 are rated based on the insulation of the internal conductors. The
internal conductors are rated a minimum of 75C. The surface of the SE is
marked with the type letter NEC designations of the individual conductors so
that they will always be either 75C or 90C (USE-2 is 90C minimum) (SE and
USE is 75C minimum).
Number Eligible to Vote: 11
Ballot Results: Affirmative: 11
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augie47 said:
I'm sorry. I don't follow. 334.80 and 338.10 seem to be intact, slightly clarified, but still present.
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See below...
338.10(B)(4)(a) Interior Installations. In addition to the provisions
of this article, Type SE service-entrance cable used for interior
wiring shall comply with the installation requirements
of Part II of Article 334, excluding 334.80. [ROP
7-133]
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. [ROP 7-133]
Click to expand...
 
Dennis Alwon said:
I am confused by this statement. The 2008 does list se cable and the proposal to eliminate the conductors from the title of Table 310.15(B)(6) was rejected. What am I missing besides some brain cells. ;)
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Hmmm.... brain cells.... what are those??? ;)

I referring to Table 310.15(B)(16), depicted in part below, in the draft (essentially the same as current Table 310.16)

Table31015B16Header.gif


310.15(B)(7)(b) sends you to this table for comparison of feeder ampacity not greater than the allowable ampacity of service conductors.

Do you see SE in the table?
 
Smart $ said:
See below...
Click to expand...
338.10(B)(4)(a) Interior Installations. In addition to the provisions
of this article, Type SE service-entrance cable used for interior
wiring shall comply with the installation requirements
of Part II of Article 334, excluding 334.80. [ROP
7-133]
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. [ROP 7-133]

so the confusion over 338.10 vs 215.2/310.15(b)(6) is now limited to SE installed in thermal insulation :smile: I'm unclear if this proposed change will clarify the need to use the 60? rating on SE "whole house feeders".
Does it clarify for you ?
 
augie47 said:
so the confusion over 338.10 vs 215.2/310.15(b)(6) is now limited to SE installed in thermal insulation :smile: I'm unclear if this proposed change will clarify the need to use the 60? rating on SE "whole house feeders".
Does it clarify for you ?
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I was always on the other side of the fence, where 338.10 never played a role on a "main" feeder, but the general consensus was split.

The proposed changed seems to clarify the former intention. Now it's simply a matter of being "IN" thermal insulation for the ampacity to be reduced to the 60?C rating. So are you saying that determination is going to be too spellbinding for many to make?
 
Smart $ said:
I was always on the other side of the fence, where 338.10 never played a role on a "main" feeder, but the general consensus was split.

The proposed changed seems to clarify the former intention. Now it's simply a matter of being "IN" thermal insulation for the ampacity to be reduced to the 60?C rating. So are you saying that determination is going to be too spellbinding for many to make?
Click to expand...

No.:grin: But, if you were one that proposed that another section (215.2 or 310.15(b)(6), took precedence over 338.10, do you see any change that would change ones mind ? The present section ('08) doesn't mention thermal insulation, but that seems to be the addition.
I;ve been on the "60? takes precedence" side of the fence, but I still see room for argument (confusion)
 
augie47 said:
No.:grin: But, if you were one that proposed that another section (215.2 or 310.15(b)(6), took precedence over 338.10, do you see any change that would change ones mind ? The present section ('08) doesn't mention thermal insulation, but that seems to be the addition.
I;ve been on the "60? takes precedence" side of the fence, but I still see room for argument (confusion)
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Yes. The thermal insulation part. Per 2008, my interpretation of 310.15(B)(6) trumping 338.10/334.80 made no consideration for thermal insulation. Never really thought about it, but it makes sense.
 
augie47 said:
... The present section ('08) doesn't mention thermal insulation, but that seems to be the addition.
I;ve been on the "60? takes precedence" side of the fence, but I still see room for argument (confusion)
Click to expand...
Well here's another worthy of debate issue on the subject...

Say the "insulation clause" is put into effect. If a Type SE cable were used as an interior feeder and only a short section of it were "in" insulation, the application of [2008] 310.15(A)(2) Exception could "trump" the insulation clause. Actually, the Exception could do that now under 2008 if most of the cable is outside.
 
so the power company will run larger wires to the house? I doubt that. unless i read it wrong they run what ever they think is good enough in the jersey state.
 
Smart $ said:
Say the "insulation clause" is put into effect. If a Type SE cable were used as an interior feeder and only a short section of it were "in" insulation, the application of [2008] 310.15(A)(2) Exception could "trump" the insulation clause. Actually, the Exception could do that now under 2008 if most of the cable is outside.
Click to expand...

That may be true in some instances but if there is fire caulk thermal insulation or sealing foam being used to seal the hole coming from the outside, then the provisions of 310.15(A)(2) exception shall not apply
 
Dennis Alwon said:
You know the article and the some instances I referred to are when two or more cables are installed thru the same hole--- 334.80
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Yeah I know that article... :roll:

...but you made it sound like the Exception didn't apply for one cable.

Additionally, if 338.10 makes it through as proposed, 334.80 will no longer be in play. As such, an SE cable, or cables, "in" thermal insulation being countermanded with 310.15(A)(2) Exception would be the only issue on the table.
 
This proposal is at "accept in principle" stage. It still has two more stages to go through before it does or does not get accepted. Also, the accept in principle type proposals sometimes get rewritten. I would wait until at least the ROC before I put too much interest into the changes.


The ROP "draft" is kind of fun to use, comparing it to the '08 makes it somewhat interesting to see how the '11 may wind up looking.
 
Pierre C Belarge said:
... I would wait until at least the ROC before I put too much interest into the changes.


The ROP "draft" is kind of fun to use, comparing it to the '08 makes it somewhat interesting to see how the '11 may wind up looking.
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"too much interest"

...but that's just it. It is interesting. Also, it provides clues as to intent of otherwise widely debatable issues. Yet no misplaced "interest" here! After all, we still have to comply with the cycle that is in effect, like it or not. :smile:
 
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