310.15(b)(6)

[ryan_618]

Something really interesting is going to happen in 2008, although nobody seems to be talking about it.

Right now, the NEC seems to imply that there can be more than one "main power feeder" to a dwelling unit.

In the 2008, it will be clarified that there can be only one, and in addition, Table 310.15(B)(6) can only be used when the main power feeder serves 100% of the loads associated with the dwelling.

Problem: What happens when I have a code compliant installation with one feeder circuit going from the outside breaker to a panelboard inside, but then I decide to add an A/C unit? If I add another breaker and feeder to the A/C, or if i tap the feeder, or if I create a second set of service entrance conductors and a new service disconnect, my feeder no longer serves 100% of the associated loads, and my formerly code compliant feeder has to be removed and replaced with a feeder complying with 310.16?

I find it strange that none of the experts I have talked to have noticed this yet. I think it could easily be one the biggest changes in the 2008 NEC.

 

[George Stolz]

Here is the comment, I hadn't noticed it either:

6-63 Log #1915 NEC-P06 Final Action: Accept

(310.15(B)(6))
____________________________________________________________
Submitter: Frederic P. Hartwell, Hartwell Electrical Services, Inc.
Comment on Proposal No: 6-61
Recommendation: Revise the second sentence to read: “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 that supplies, either by branch circuits, or by feeders, or both, all loads that are part or associated with the dwelling unit.”​

Substantiation: The submitter wishes to express his sincere appreciation to CMP 6 for their panel statement. It is a perfectly worded statement of intent, one that the submitter has been pursuing for the last six cycles or so. This comment attempts to make the text of the rule convey the objectives of the statement. The wording clarifies that the dwelling could have a subpanel, as long as it is fed from the main panel so that the load diversity of the subpanel loads is included within the load profile of the main feeder. The comment wording also includes associated loads, as would be the case where there was a detached garage. Finally, the comment deletes the terminology “lighting and appliance branch-circuit” because CMP 9 is removing this from Article 408 (Proposal 9-117).​

Panel Meeting Action: Accept
Number Eligible to Vote: 11​

Ballot Results: Affirmative: 11

Initial reaction: good change.

Problem: What happens when I have a code compliant installation with one feeder circuit going from the outside breaker to a panelboard inside, but then I decide to add an A/C unit?

How would you have worded it? As it was, it was vague, now this is clear; do you think enforcement will be "to the letter" when dealing with old work? Most AHJ's I've encountered have been somewhat liberal when dealing with old work situations.​

It is a fairly substantial change to have made it under the radar so far. ​

 

[ryan_618]

I wouldn't have made the change. Has there been any problem on this? In the city that I work, 400A services are very common. We use (2) 200A breakers outside to feed (2) 200A panels inside. We used Table (B)(6) for each feeded, because I think the 2005 allowed it. Now we will not be able to do this anymore, unless we increase our wire size.

 

[Dennis Alwon]

I wouldn't have made the change. Has there been any problem on this? In the city that I work, 400A services are very common. We use (2) 200A breakers outside to feed (2) 200A panels inside. We used Table (B)(6) for each feeded, because I think the 2005 allowed it. Now we will not be able to do this anymore, unless we increase our wire size.

I always thought that Table 310.15(B)(6) really didn't apply in the case of 2- 200 amp panels even though it was allowed by most inspectors. The Table only allows 400mcm copper for 400 amp service. It never said you could use 2/0 copper twice. I know that most areas allow it but I remember years back when one of our jurisdiction made us pull 3/0 for 2- 200 amp panels.

 

[Pierre C Belarge]

What I also find interesting about this and other changes like it is, that the jurisdictions that may not make a move to the '08 for many years to come are or may be causing the installations they permit to actually become noncompliant in the future years. It is sort of like those jurisdictions are looking towards the future, seeing the future and specifically ignoring the future.... it really makes me wonder sometimes why are we even following the code anyway???????

 

[JohnJ0906]

In the case of 400 amp services, we use (2) 4/0 al seu cable from meter outside to (2) 200 amp Main breaker load centers inside. Every jurisdiction (that I am aware of) around here accepts this.

 

[ryan_618]

In the case of 400 amp services, we use (2) 4/0 al seu cable from meter outside to (2) 200 amp Main breaker load centers inside. Every jurisdiction (that I am aware of) around here accepts this.

Not for long...

 

[suemarkp]

If you split the service into two sets before the main disconnects, then these are service conductors and not feeders. Isn't the language allowing service conductors still there? There would be no main power feeder in this case.

I saw the new definition for 2008 and was disappointed. I forsaw the same things you did (a metermain type service with an outside breaker, for say an AC compressor).

I think the real way to solve this whole issue is to define a panelboard type of "diversified panelboard". This may be difficult to define, but I'd say if it had 5 or more 15 to 20 120V amp circuits that all contributed to a calculated load, and it is on residential property, then the panelboard is diversified and table 310.15(B)(6) should be allowed.

It is crazyness to say a 200A residential panelboard isn't diversified in 99% of the cases when a little 100A panel for the 1200 square foot house is. I'll bend and say its not diversified if you have a 200A panelboard with nothing but heat pumps on it, but that would be quite rare.

 

[curt swartz]

Not for long...

As long as the calculated load does not exceed 180 amps why wouldn?t 4/0 AL be acceptable?

 

[curt swartz]

It sounds like they are just changing the wording back to what it was in previous additions (80?s and early 90?s).

 

[bphgravity]

However, the main power feeder should never be required to be larger than the service conductors. So in the case where 2/0 CU service conductors are used for a 200A dwelling service, why would you be required to install a 3/0 CU feeder to the lighting and appliance panelboard, even if one or more loads is supplied from the serivce panel and not the feeder?

 

[charlie b]

I have always interpreted that article in the manner conveyed in the 2008 version. We have debated this issue on this Forum at least once, and I think twice. Each time, I supported the view that there can be only one ?main feeder,? in the context intended by that article. This is nothing new to me; it clarifies the rule to mean what I already thought that it meant.

As to the disposition of installations that were previously considered ?code compliant,? under the 2005 or earlier editions, they will become non-compliant under 2008. But that doesn?t mean they have to be changed out. The ?Grandfather Rule? will permit them to remain, unless the local AHJ makes a ruling to the contrary (something about creating a danger to occupants).

 

[winnie]

As I've stated on the past in this topic, I belive that the basic approach used for 310.15(B)(6) is wrong. IMHO the service _calculations_ for a residence (or perhaps _any_ occupancy) should return two values: conductor ampacity and OCPD trip rating. There are many places in code where the OCPD is permitted to exceed conductor ampacity; this is just another one. But that is a discussion for another time.

I don't know how to get the wording right, but IMHO if a particular feeder carries a set of loads that _could_ reasonably be considered _a_ complete dwelling, than that feeder should qualify for the sizing of 310.15(B)(6), even if that feeder is not the entire load of the particular dwelling in question. This speaks directly to Ryan's example. Call the house pre air conditioning 'dwelling A', and call the house with air conditioning 'dwelling B'. A feeder sufficient for _all_ 'dwelling A' should still fall under 310.15(B)(6), even though it is now only a portion of the load in 'dwelling B'.

-Jon

 

[radiopet]

2008 ROC 310.15(B)(6)

(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services
and Feeders. For individual dwelling units of onefamily,
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 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. [ROP 6–61, 9–7e]

2005 NEC 310.15(B)(6)

(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(s) between
the main disconnect and the lighting and appliance branchcircuit
panelboards(s). 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.

Ryan you stated : In the 2008, it will be clarified that there can be only one, and in addition, Table 310.15(B)(6) can only be used when the main power feeder serves 100% of the loads associated with the dwelling.

Are you saying you believe the removal of the items I underlined in the 2005 NEC above and the remooval of the (s's) denote this as a clear statement that clarifies they can only be one . While I like that it is being cleaned up I guess I don't read between the lines that well on the statement.

Please clarify for me more...if you dont mind.

 

[iwire]

We have debated this issue on this Forum at least once, and I think twice. Each time, I supported the view that there can be only one ?main feeder,? in the context intended by that article.

I support that view as well.

 

[ryan_618]

Paul, it appears you have quoted the ROP draft, not the accepted ROC comment. Refer to accepted comment 6-63 by Fred Hartwell, and you will notice not only the removal of the (s) in the requirement, but also an additional statement clarifying that the feeder (or service conductor) must serve "all loads that are part or associated with the dwelling unit."

 

[radiopet]

Yeah..Yeah........thats what I mean.....I seem to can't find the location of the latest comments.....can you link me to where I can get it..is the one on the NFPA one updated?

Oh....wait is this what you are refering too....

Are you refering to this...

6-63 Log #1915 NEC-P06 Final Action: Accept

(310.15(B)(6))
__________________________________________________ __________
Submitter: Frederic P. Hartwell, Hartwell Electrical Services, Inc.
Comment on Proposal No: 6-61
Recommendation: Revise the second sentence to read: “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 that supplies, either by branch circuits, or by feeders, or both, all loads that are part or associated with the dwelling unit.”


Substantiation: The submitter wishes to express his sincere appreciation to CMP 6 for their panel statement. It is a perfectly worded statement of intent, one that the submitter has been pursuing for the last six cycles or so. This comment attempts to make the text of the rule convey the objectives of the statement. The wording clarifies that the dwelling could have a subpanel, as long as it is fed from the main panel so that the load diversity of the subpanel loads is included within the load profile of the main feeder. The comment wording also includes associated loads, as would be the case where there was a detached garage. Finally, the comment deletes the terminology “lighting and appliance branch-circuit” because CMP 9 is removing this from Article 408 (Proposal 9-117).


Panel Meeting Action: Accept
Number Eligible to Vote: 11

Ballot Results: Affirmative: 11

Hmmm.....guess I am losing something in translation........think I need to retire.....

"the main power feeder shall be the feeder between the main disconnect and the lighting and appliance branch circuit panelboard that supplies, either by branch circuits, or by feeders, or both, all loads that are part or associated with the dwelling unit."

Guess I am just not looking at the whole picture because me and mike have talked about this before....and I am not sure how this effects the point between the Meter Enclosure and the Main Disconnect locations and the use of (2) sets of 4/0 AL lets say in a (320A ) service setup.

Flame all you want people....I am trying to understand it myself before the 2008 is released...have not even really started looking at it.

 

[charlie b]

....and I am not sure how this effects the point between the Meter Enclosure and the Main Disconnect locations and the use of (2) sets of 4/0 AL lets say in a (320A ) service setup.

One effect is that you can?t use it for main disconnect locations (plural). Another effect is that can?t use it if you intend to parallel the service conductors. But then, IMHO you could never do either of these things anyway. This is just a clarification of what I believe the code already required.

As to paralleling service conductors, I invite your attention to the fact that Table 310.B(6) is not about ?ampacity.? It does not declare that a 4/0 aluminum service conductor has an "ampacity" of 200 amps. Therefore, you cannot infer that a pair of 4/0 will have an ampacity of 400 amps, and conclude that this would be acceptable for a 320 amp service. That table says that if you have a service load of XXX, you can use size YYY as the service conductors. Paralleling is not allowed, unless you go somewhere else to find the ampacity of the conductors you intend to place in parallel.

 

[radiopet]

The reason I am bringing that up is the wide acceptance of the exact senerio I stated. See it all the time and many have stated it here as well. I guess the concern was I did not see exactly how the revision posted clears up that exact thing.....

I do see how it clears up the example Ryan gave......

Maybe I got lost in the other posts and got off Ryans example....quite possible for me...lol

310.4 Conductors in Parallel. Aluminum, copper-clad
aluminum, or copper conductors of size 1/0 AWG and
larger, comprising each phase, polarity, neutral, or
grounded circuit conductor, shall be permitted to be connected
in parallel (electrically joined at both ends).

And I understand about the paralleling statement above.....

Not argueing the semantics point charlie.....just think the whole thing could be better defined is all.


OK I will let this go...but I personally feel the change in the verbiage to 310.15(B)(6) sets us back to the 90's.....and I wont go into why but Mr. Holt agrees and he can probably explain it MUCH better than I can......thats usually my problem with typing..I say it better than I type it...

 

[gndrod]

I agree with the 'split' service conductor also, but is the meter connections designed for double lugging to quailfy the terminal rating? Just curious. rbj