310.15(b)(6)

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augie47

augie47

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State Electrical Inspector (Retired)
Now that the 'o8 Code has calrifierd the wording of 310.15(B)(6) is the following correct ?
I build a 200 amp serivce, based on the table, I have a 4/0 AL riser.
I feed an outside feed-thru disconnect with my 4/0 AL. I add a 15 amp 2 poe breaker at the outsidepanel and feed an HVAC condensor unit for the gas furnace. I then run a interior feeder to the interior panel for all the other house load. Since the feeder is no longer carrying "all loads associted with he dwelling", it will need to be a 300 kcmil (AL) Correct ?

a 2nd queston. If that outside panel has a 15 amp branch circuit feeding a detached garage (and no condensor) since that garage is "associted with the dwelling" is my house feeder still required to be a 300 kcmil (AL) ?
 
I would say yes twice but I didn't check your wire sizes. To make matters worse use se cable to the interior panel---ugh....
 
I should clarify, sorry, the scenerio was based on SE cable and the new 338.10(B)(4) rule.
 
I would say yes to both also ,.. and notice with less load imposed on the interior panel the wire has to be increased in size ,.. so ,...in other words,.. if you feed all the load off the main power feeder/ interior panel it is allowed to be a smaller 4/0 al conductor..

I don't know if those that wrote this article understand the idiocy that they have written into the sacred scratching.
 
augie47 said:
Now that the 'o8 Code has calrifierd the wording of 310.15(B)(6) is the following correct ?
I build a 200 amp serivce, based on the table, I have a 4/0 AL riser.
I feed an outside feed-thru disconnect with my 4/0 AL. I add a 15 amp 2 poe breaker at the outsidepanel and feed an HVAC condensor unit for the gas furnace. I then run a interior feeder to the interior panel for all the other house load. Since the feeder is no longer carrying "all loads associted with he dwelling", it will need to be a 300 kcmil (AL) Correct ?

a 2nd queston. If that outside panel has a 15 amp branch circuit feeding a detached garage (and no condensor) since that garage is "associted with the dwelling" is my house feeder still required to be a 300 kcmil (AL) ?
Click to expand...

I say the 4/0 AL is allowed in both situations.

215.2(A)(3)
 
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ceb58 said:
I dont know about binding cheese but I agree with John on 215.3 (A) (3)
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I'm not diagreeing, well I guess I am, but if we were installing a 100 amp feeder to a heating unit using SE we would have to use 1/0 AL under the new rule.. so there we have a feeder serving something other than the dwelling unit so we apply 338.10. In the scenerio I spelled out we have a feeder serving something other than the entire dwelling unit but we are not using 338.10.
I think the CMP didn't go far enough on this.
 
"I say the 4/0 AL is allowed in both situations."

Ditto - 310.15(B)(6) - 2nd to last sentence, "The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors."
 
You are winning me over, but I still have mixed thoughts.
What about ambient or derating. If our feeder was subject to ambient or derating would we not need to increrase the size then ?
Is 338.10. that much different ? Our 4/0 service might be XHHW without the limitations placed on SEU. Do we then ignore the 338.10 restrictions ??

Don't get me wrong, I think the 215.2 posts make sense, I just want to be sure.
 
dana1028 said:
"I say the 4/0 AL is allowed in both situations."

Ditto - 310.15(B)(6) - 2nd to last sentence, "The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors."
Click to expand...

Very good arguements. I have a phone call into our state DOI head on another issue and I will have to run these by him because he is very adamant about running the larger conductors/feeders.

My only counterpoint, just strictly off the top of my head, would be (1) I do not think it affects the new ruling on SE cable and (2) if your set up is a meter combo with breakers feeding invidual circuits and 200 amp feeder to house panel, is that there are no SE conductors to compare wire size with. Don't get me wrong, I am all for running the feeders according to '05 and before, but this is the one code section I do not want to get tagged on if for nothing more the the financial costs of "correcting" it.
 
P.S. My answer to the original post, based on conversations with various inspectors and DOI is that, yes, you need the 300 kcmil. I do not think the fact that your other load is detatched has anything to do with it. It is all part of the same load calculation.
 
dana1028 said:
"I say the 4/0 AL is allowed in both situations."

Ditto - 310.15(B)(6) - 2nd to last sentence, "The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors."
Click to expand...


You quote states shall not be required to have an allowable ampacity rating greater than their service entrance conductors. Well the ampacity of a large conductor can be lower than a smaller one. Since the allowable ampacity in T310.15(B)(6) is 4/0 for a 200 amp service on a dwelling. That same 4/0 conductor as part of an se cable and used as a feeder must follow 310.15. In the latter case 4/0 is only good for 150 amps.
 
Dennis Alwon said:
That same 4/0 conductor as part of an se cable and used as a feeder must follow 310.15. In the latter case 4/0 is only good for 150 amps.
Click to expand...

Is that a more code accurate way of saying what I said earlier? :smile: I never can word those things like you guys.

BTW, my wife and I are going to a concert in Durham Thurs night. Would you like to coordinate a time I can wave to you as we go by (sorta kinda :rolleyes:). :D
 
Another way to look at it ,.. the table 310.15(B)(6) is not an ampacity table ,..it does not change the ampacity of a 4/0 aluminum ..
 
Dennis Alwon said:
You quote states shall not be required to have an allowable ampacity rating greater than their service entrance conductors. Well the ampacity of a large conductor can be lower than a smaller one. Since the allowable ampacity in T310.15(B)(6) is 4/0 for a 200 amp service on a dwelling. That same 4/0 conductor as part of an se cable and used as a feeder must follow 310.15. In the latter case 4/0 is only good for 150 amps.
Click to expand...
The term "ampacity" is not used in 215.2(A)(3).

"Feeder conductors for individual dwelling units or mobile homes need not be larger than service conductors."

Derateing or temperature adjustment aside, there is no logic whatsoever to have 300 kcmil as a feeder that will carry LESS load that the 4/0 service conductors. (Yes I know logic has no place in the NEC :grin:)
 
Thought I would post this



6-61 Log #194 NEC-P06 Final Action: Accept in Principle
(310.15(B)(6))
____________________________________________________________
NOTE: The following proposal consists of Comment 6-40 on Proposal 6-41
in the 2004 May Meeting National Electrical Code Committee Report on
Proposals. This comment was held for further study during the processing
of the 2004 NATIONAL ELECTRICAL CODE. The recommendation in
Proposal 6-41 was:
Revise as follows:
(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders.
For individual units of one family, two-family and Multifamily dwelling
units, 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 to a 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(s) between the main
disconnect and the lighting and appliance branch-circuit panelboards(s).
The feeder conductor to a dwelling each unit shall not be required to be
larger than their service-entrance conductors. The grounded conductor
shall be permitted to be smaller than the ungrounded conductors,
provided the requirements of 215.2, 220.22, and 230.42 are met.
Submitter: Frederic P. Hartwell, Hartwell Electrical Services, Inc.
Recommendation: Accept the panel action in principle. Clarify the
permissible application of the multiple feeder allowances as one of the
following four options:
1) “... the main power feeder shall include the feeder(s) serving only loads
associated with a single dwelling unit and running to but not originating in the
lighting and appliance branch-circuit panelboard(s) serving the dwelling unit.”
OR
2) “... the main power feeder shall include the feeder(s) serving only loads
associated with a single dwelling unit and running to the lighting and appliance
branch-circuit panelboard(s) serving the dwelling unit.” OR
3) “... the main power feeder shall include the feeder(s) serving only dwelling
loads and running between the main disconnect and the lighting and appliance
branch-circuit panelboard(s) serving the dwelling unit.” OR
4) “... the main power feeder shall include the feeder(s) serving only dwelling
loads and running to but not originating in the lighting and appliance branch-
circuit panelboard(s) serving a particular dwelling unit.”
Substantiation: By clarifying that this note applies to dwelling units within
multifamily housing, which is well advised, the proposal raises important
questions as to exactly which panelboard feeders are within the scope of this
allowance. Options 1 and 2 exclude feeders that are comprised of dwelling
loads, but that serve multiple dwelling units. Options 3 and 4 allow such a
feeder. Options 1 and 2 as a group and options 3 and 4 as a group sort out
whether this allowance applies to subpanel feeders within a dwelling unit.
Dwelling unit subpanel loads do not present the same diversity as dwelling unit
panels serving the entire dwelling unit, and thereby undercut one of the
traditional supporting assumptions underlying these allowances. However, all
of these interpretations are possible given the ambiguous “(s)” endings on the
word “feeder” and “panelboard.” CMP 6 needs to clarify exactly which feeders
qualify for this allowance.

Panel Meeting Action: Accept in Principle

Remove the 2 sets of parentheses and the duplicate “s” on panelboards so that
the section reads:

(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 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 lighting and appliance
branch-circuit panelboard. 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.

Panel Statement:

The panel agrees that the present wording is ambiguous. It is
the panel’s intent that this allowance apply only to conductors carrying 100%
of the dwelling unit’s diversified load.
Number Eligible to Vote: 11
Ballot Results: Affirmative: 11
Click to expand...
 
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