310.15(B)(6) Main Power Feeder.

Status
Not open for further replies.
Re: 310.15(B)(6) Main Power Feeder.

Mike, here is an old post in agreement with you.

posted December 20, 2002 10:38 PM
--------------------------------------------------------------------------------
OK let's do this.
There is no reduction
allowed after the lighting appliance branch-circuit panel(s).

This article specifically allows reduction to the first lighting appliance branch-circuit panel(s) down line of the service equipment.

We will use a lateral in this example

400A service
2-200 amp lighting appliance branch-circuit panels.

Service lateral --400KCM copper per article 310.15(b)(6) to 400A OCPD.

We still have not made it to our lighting appliance branch-circuit panels yet.

For sake of coversation we install 2-200 amp enclosed breakers adjacent to this 400 amp OCPD and feed these from parallel lugs.

We use 2/0 copper per 310.15(b)(6).

We still have not made it to our lighting appliance branch-circuit panels yet.

We feed 2-200 amp lighting appliance branch-circuit panels with 2/0 copper per 310.15(b)(6)and make all terminations.

We have finally made it to our lighting appliance branch-circuit panels.

Now 310.15(b)(6) has seen it's end and if we feed any sub panel, say a 100 amp, from one of these aforementioned lighting appliance branch-circuit panels, this 100 amp sub panel can not use 310.15(b)(6)

Roger
Click to expand...
Roger
 
Re: 310.15(B)(6) Main Power Feeder.

Sorry, Mike, I wasn't clear in my post, or perhaps I just didn't correctly interpret your comment. For any given, single, dwelling unit (including cases where one service provides power to several dwelling units), the conductors from the main disconnect to the first panelboard in that dwelling unit can use 310.15(B)(6). In your example, from the service disconnect (consisting of two breakers) you have two sets of conductors going to two L&A panelboards. I agree that the two feeders collectively comprise the "main power feeder" to that one dwelling unit, and you can use 310.15(B)(6) for both feeders.

My comment was focused on panels that are not fed directly from the main disconnect. If you have one panel sub-fed from the first panel, regardless of whether via feed-through lugs or via a breaker in the first panel, then the feeder from the first panel to the second cannot use 310.15(B)(6).
 
Re: 310.15(B)(6) Main Power Feeder.

Georgestloz, I was referring to the original question, if you install a panel on the outside of a structure with a main and additional breaker spaces (for what ever the use), if this panel has what I call, feed thru lugs and from these lugs there are conductors to a panel on the interior of the structure, the conductors from the main panel to what I call a sub-panel ( these conductors would be called Main power feeders not feeders) If you turn off the main , there would be no power downstream from it.
I think David said the very same thing in his statement.
 
Re: 310.15(B)(6) Main Power Feeder.

Just to throw a kinck in this tread how doses 215.2(a)(3) play on this. As I see it If you had a feeder the same amp as the service. why would you have planed for more load at meter/panel? You should down size feeder or up size service. in the case of this thread I would say it is not a main feeder. it would need to come off of the main disconect. Not a panel bus between.
 
Re: 310.15(B)(6) Main Power Feeder.

Donnie, There is no code justification for allowing a feed-through-lug-fed feeder to use the table, and disallowing a feeder supplied from a breaker in the same location.

How the feeder is terminated is not one of the discriminating characteristics, of which we already have many. The termination method is irrelevant, IMO.
 
Re: 310.15(B)(6) Main Power Feeder.

Originally posted by charlie b (w/ Roger & Mike concurring):
I agree that the two feeders collectively comprise the "main power feeder" to that one dwelling unit, and you can use 310.15(B)(6) for both feeders.
Click to expand...
I don't agree. "...feeder conductors that serve as the main power feeder to each dwelling unit..." describes multiple conductors inside each feeder. A feeder must consist of multiple conductors (due to physics).

Two panels sharing half the load of a dwelling unit are not one feeder, they're two. If one is larger than the other, or carries more of the load, then it is the main power feeder, and the other is not. I don't see how you could have two main power feeders for the same location. They're individuals.

Here's my opinion:

:D

[ February 28, 2006, 10:45 PM: Message edited by: georgestolz ]
 
Re: 310.15(B)(6) Main Power Feeder.

__________________________________________________
________________________________________
Originally posted by david: This section is only addressing the main power feeders to a dwelling unit.
________________________________________
You have a slight mis-quote. Instead of saying "a dwelling unit," you should say "each dwelling unit." The rule applies to two-family dwelling units and to multi-family dwelling units.
__________________________________________________

Just for clarification you are correct I should have said:

This section is only addressing the main power feeder to a dwelling unit or
This section is only addressing the main power feeder conductors to a dwelling unit.
The dwelling unit is singular and the feeder is singular in the first sentence.

We get into the Feeder(s) dwelling unit(s) in the second sentence. I would agree for a building with one service supplying multiple dwelling(s) you now need feeder(s)
 
Re: 310.15(B)(6) Main Power Feeder.

As far as applying this section to an individual dwelling unit in a single family dwelling we still have to look at:

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 panelboard(s).

We have the main disconnect singular (the main disconnect for a dwelling)
The main power feeder singular to the lighting and appliance branch circuit panelboard. So we have a main disconnect feeding a feeder to the lighting and appliance branch circuit panelboard

But we also have a main disconnect by a feeder or feeder(s) to the lighting and appliance branch circuit panelboard or panelboard(s)

Since this section allows for a main disconnect for a dwelling to supply feeders to panel boards there is no way to make this section exclusive.

The main power feeder singular from a main disconnect for the dwelling can include feeders plural to panelbords plural.

This is my opinion

[ March 01, 2006, 06:07 AM: Message edited by: david ]
 
Re: 310.15(B)(6) Main Power Feeder.

George I have said many times before that I have a hard time understanding some things so I need help understanding just what is happening here

I think that what I am seeing is:
(1) These conductors are the service entrance conductors that is supplying a eight circuit panel
(2) These conductors are coming off the lugs at the bottom of the panel to feed unit 1 and are protected by, What?
(3) These conductors are coming off breaker 6 & 8 to feed a panel in unit 2 which has another panel feed from it with conductors (4)
(5) These conductors are protected from breakers 2 & 4 that supply the pool.

Am I correct about your drawing? :)
 
Re: 310.15(B)(6) Main Power Feeder.

I think that what I am seeing is:
(1) These conductors are the service entrance conductors that is supplying a eight circuit panel
Yes, an 8 space metermain with feedthrough lugs.

(2) These conductors are coming off the lugs at the bottom of the panel to feed unit 1 and are protected by, What?
The main breaker. I included that to include Donnie's description.

(3) These conductors are coming off breaker 6 & 8 to feed a panel in unit 2 which has another panel fed from it with conductors (4)
Yes.

(5) These conductors are protected from breakers 2 & 4 that supply the pool.
Yes.

If I am correct then your service has failed big time.
Please, elaborate.

1. If it's easier to envision with meters between the three feeders at the main disconnect, let you imagination run wild. But I don't believe there is any such requirement, technically. :)

3. So what are you failing it on? :D
Click to expand...
 
Re: 310.15(B)(6) Main Power Feeder.

George, in your drawing, there is no way that the feeder going to panel 3,4 or 5 can be considered a main power feeder.
 
Re: 310.15(B)(6) Main Power Feeder.

Originally posted by georgestolz:
I think that what I am seeing is:
(1) These conductors are the service entrance conductors that is supplying a eight circuit panel

Yes, an 8 space metermain with feedthrough lugs.

2. The feeder to unit 1 can be huge, there's nothing saying it's not. :)

3. So what are you failing it on? :)
Click to expand...
Click to expand...
 
Re: 310.15(B)(6) Main Power Feeder.

George: I agree with your "can" and "cannot" statements for 1 through 5, but not 6. I agree with your reasons for 2 through 5, but not 1.

The reason #1 cannot use 310.15(B)(6) is not that it serves more than one dwelling unit. The rule is that the main feeder starts at the disconnect, and goes to one dwelling unit. Your #1 cable comes from the utility and ends at the disconnect, so it is not covered by the NEC.

There seems to be some confusion with regard to the singulars and plurals. I believe the plurals were originally intended to address a disconnect that serves two or more dwelling units. Conductors that begin at the disconnect and that end at the first panelboard in each dwelling unit can be sized per 310.15(B)(6). However, as I read the words, and as Mike appears to have read the words, if a single dwelling unit is served via two feeders to two separate panels, the words do not prohibit applying 310.15(B)(6) to both feeders. I don't believe that was the intent of the authors, but I do believe that that is what the words say.

So Mike, I believe this aspect of your posted opinion is correct, but I wish it weren't. I would like to see a revision to this section, but I don't know if it will happen in 2008.
 
Re: 310.15(B)(6) Main Power Feeder.

Originally posted by charlie b: The reason #1 cannot use 310.15(B)(6) is not that it serves more than one dwelling unit. The rule is that the main feeder starts at the disconnect, and goes to one dwelling unit. Your #1 cable comes from the utility and ends at the disconnect, so it is not covered by the NEC.
Click to expand...
(For ease of reference, here's the picture by itself).

Charlie, this rule applies to service laterals and service entrance conductors. They are not included in the "main power feeder" portion of the text, but they are still named.

Charlie (On the two-feeders for one unit issue):
I don't believe that was the intent of the authors, but I do believe that that is what the words say.
Click to expand...
I completely agree with your analysis. I would change my answer to #6 to yes, both feeders could use this table.

Originally posted by jwelectric:
Those conductors coming off the main lugs at the bottom of the panel supplying unit 1 can be no smaller than the overcurrent device that is protecting the panel.
Click to expand...
I never said they weren't. Say it's a 200 amp service, with a 100 amp feeder for Unit 2, and a 200 amp feeder for Unit 1. Calculated load on each unit is 54 amps.
Done. :D

Originally posted by Donnie:
George, in your drawing, there is no way that the feeder going to panel 3,4 or 5 can be considered a main power feeder.
Click to expand...
Please substantiate your opinion with some code text. How on earth could a multifamily dwelling hope to make use of this table if a breaker broke the deal? Think about a 16-plex. Each Main Power Feeder can use 310.15(B)(6). By Article 230, we can only have six throws of the hand. Therefore, a main disconnect is required. Therefore, unless each unit is getting a feeder worth over a 1000 amps, there has to be a circuit breaker present.

I'm not picking on you, it just seems as though you might be using your gut more than your reason in your opinion.
 
Re: 310.15(B)(6) Main Power Feeder.

I think that we need to look at what this section says and not what we wish it said. The plurals were included for a reason. Charlie thinks it was for multiple dwelling units and others think it includes multiple panels within a single dwelling unit. The fact that the plurals are included without comment referring to either multiple dwellings or multiple panels within a single dwelling means that the section can be used for both in my opinion.

And I think we also need to take a look at what we're doing here. Why would it be okay to run reduced sized (or increased ampacity--however you want to look at it) service entrance conductors to serve the entire load for a dwelling unit, but not do the same for another panel, within the same dwelling unit, which only serves a small portion of the load? As long as that panel meets the definition of main power feeder in 310.15(B)(6), meaning it's located between the main disconnect and a lighting and appliance panelboard, I'd say you can. Even if the main disconnect is located on a lighting and appliance panelboard. Now, feeders run to outbuildings or other structures that are not dwelling units are another story.

That having been said, what I prefer to see is all service entrance and feeder conductors run full size per Table 310.16. But the Code allows them to be sized to 310.15(B)(6), so that's what I approve.
 
Re: 310.15(B)(6) Main Power Feeder.

Originally posted by georgestolz: Charlie, this rule applies to service laterals and service entrance conductors. They are not included in the "main power feeder" portion of the text, but they are still named.
Click to expand...
Yep. You're right. I withdraw my earlier (erroneous) comment concerning your drawing's item #1.
 
Status
Not open for further replies.
Top