Still trying to make sense of SER wire size.

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I so do not understand what is being argued here. I haven't been able to devote much time here for the past couple weeks, but I've skimmed through here and not gotten it.

Could everybody clarify what their position is, on whatever's being argued, in two paragraphs or less? I want to participate. :D


(If this provides something to point out in describing, please feel free to use it.) :)
 
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215 and 225 apply but I don't see wording in 215.2(A)(3) that limits the application of 310.15(B)(6) to only certain feeders. . 310.15(B)(6) has limitations in its wording, but I don't see limitation in 215.2.
"Paragraph 310.15(B)(6) shall be permited to be used ....." is commenting about what it's commenting about. . Or in other words, it applies to the situation it's talking about and makes no comment or restriction on other scenerios.

215 and 225 clearly can restrict feeders. . But does it restrict the application of 310.15(B)(6) further than 310.15(B)(6) restricts itself ? . If it does, I don't see the wording in what I'm reading.

I agree with Mark

suemarkp said:
What matters is what the code says, not what it doesn't say. 215.2(A)(3) says feeders for individual dwelling units can use 310.15(B)(6) for conductor size. It is not clear if that last sentence is modifying the previous sentence (which would be redundant since service conductors we know can be sized by 310.15(B)(6)), or it if it is a separate statement.

It is not clear what feeder is being referenced -- one as big as the service or any dwelling unit feeder. All it does is send us back to the confusing wording of 310.15(B)(6) which does limit the use to main power feeders and the specific definition of that feeder type defined in that section.
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David
 
David

Let?s look at this a different way and maybe we can see it a little different.

Using section 220.82 a calculation for a service comes to exactly 48,000 VA.
Using Table 310.15(B)(6) would a 2/0 copper conductor be allowed to be installed for the Service Entrance? Yes.
If there was a meter main combo installed on the outside of the dwelling and feeders installed to the inside panel could 2/0 copper conductors be installed? Yes

Using 215.2(A) I have a load of 24,000VA noncontinuous and a 19,200VA continuous (total of 48,000) what size conductor would be required? 3/0 copper

An apartment building each individual dwelling unit has a calculated load of 48,000VA load. Using 215.2(A)(3) each individual dwelling unit would be allowed to be fed using a 2/0 copper feeder conductors.

This apartment job has a house panel that will be carrying the hall and parking lot lights as well as a pool and various other loads have a calculated load of 48,000VA. What size feeders will be required for this panel? 3/0 this panel is not supplying a dwelling unit

A single family dwelling unit has a 200 amp service installed with a 100 amp subpanel installed on the second floor. These feeders to the 100 amp panel are not supplying an individual dwelling unit nor are they the main power feeder and will require #3 copper conductors.

What controls the size of the feeders are 215.2(A)(3) which states that the feeders that supply individual dwelling units meaning they must be supplying one dwelling unit and 310.15(B)(6) which states that they must be the main power feeder.
A subpanel installed downstream of the main panel such as a panel on the second floor or a panel installed for air conditioning units would not fit the description of a individual dwelling unit nor the main power feeders for an individual dwelling unit therefore Table 310.15(B)(6) cannot be used to size these feeders.
 
I agree with everything you said except the last sentence

jwelectric said:
What controls the size of the feeders are 215.2(A)(3) which states that the feeders that supply individual dwelling units meaning they must be supplying one dwelling unit and 310.15(B)(6) which states that they must be the main power feeder.
A subpanel installed downstream of the main panel such as a panel on the second floor or a panel installed for air conditioning units would not fit the description of a individual dwelling unit nor the main power feeders for an individual dwelling unit therefore Table 310.15(B)(6) cannot be used to size these feeders.
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What controls the size of the feeders are 215.2(A)(3) which states that the feeders that supply individual dwelling units meaning they must be supplying one dwelling unit and 310.15(B)(6) which states that they must be the main power feeder.
A subpanel installed downstream of the main panel such as a panel on the second floor or a panel installed for air conditioning units would not fit the description of a individual dwelling unit nor the main power feeders for an individual dwelling unit therefore the information in 215.2(A)(3) doesn't apply.

David
 
Mike, I see what you are saying and it does make sense , more sense than how it is written. It gets alittle sticky for me around the use of the word "for"
these feeders are for an individual dwelling , not all of it I grant you but they serve it and they are feeders. I think for the sake of erring on the side of safety I'll be putting # 2 ser Al on 90 amp breakers. It is very common to use a 100 amp,.. most inspectors and electricians just kind of got in the habit I guess . I'm not sure what the danger is ,..in most applications in individual dwellings there is a $#!+ load of diversity
215.2 Minimum Rating and size


215.2(A)(3) Individual Dwelling Unit or Mobiloe Home Conductors .Feeder conductors for individual dwelling units or mobile homes need not be larger than service conductors. Paragraph 310.15(B)(6) shall be permitted to be used for conductor size.
 
georgestolz said:
I so do not understand what is being argued here. I haven't been able to devote much time here for the past couple weeks, but I've skimmed through here and not gotten it.

Could everybody clarify what their position is, on whatever's being argued, in two paragraphs or less? I want to participate.
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We weren't arguing this, but can't #1 be sized per 310.15(B)(6) since it is a service conductor for a dwelling? I think we take that as a given.

Some issues under debate:
If feeders 2 and 3 were for the same dwelling, are they "between the main disconnect and the lighting and appliance panelboard(s)"? Can they both be sized to 310.15(B)(6) if they both serve the same dwelling?

Similar question for feeder #5 if the pool was inside the house. I'll concede that an outbuilding containing a pool feeder is not a dwelling.

Finally, are your answers different if there is a single main disconnect in the first panel, or a set of 3 separate grouped disconnects (one for each feeder)?

The consensus here is usually that "main power feeder" means all the dwelling load must be on that feeder. I don't see the code words that mandate that.
 
M. D. said:
Mike, I see what you are saying and it does make sense , more sense than how it is written. It gets alittle sticky for me around the use of the word "for"
these feeders are for an individual dwelling , not all of it I grant you but they serve it and they are feeders. I think for the sake of erring on the side of safety I'll be putting # 2 ser Al on 90 amp breakers. It is very common to use a 100 amp,.. most inspectors and electricians just kind of got in the habit I guess . I'm not sure what the danger is ,..in most applications in individual dwellings there is a $#!+ load of diversity
215.2 Minimum Rating and size


215.2(A)(3) Individual Dwelling Unit or Mobiloe Home Conductors .Feeder conductors for individual dwelling units or mobile homes need not be larger than service conductors. Paragraph 310.15(B)(6) shall be permitted to be used for conductor size.
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I agree with this statement. This is such a ridiculous and confusing topic we are dealing with that it is just a safer bet to put the #2 SER on a 90 amp breaker and be done with it, although as I stated earlier, I have been putting them on 100 amp breakers for years. I understand the viewpoints that have been given here and the explanations that go along with them. I would just like to throw a little bit different spin on this topic. It has been an ongoing debate as to what qualifies as a "main feeder" and what set of circumstances need to be in place for table 310-15(B)(6) to apply. Now this is my question. Why is it that we are not asking WHY...........I'll go along with the arguement that the code is stating that 310-15(B)(6) only applies to the main feeders coming into the main disconnect. But again, WHY are we refered to 310.16 for everything else. I just can't get past the scenerio in which if a service on a home is 100 amp and fed with a #2 SE cable into a meter can with the main disconnecting means incorporated in it, that the wire size now needs to be jumped up to a #1 SER to feed into the panel. This is senseless to me and there should be some refining to make things more uniform in the code. With all that has been said here, I see no reason or purpose for 310.15(B)(6). Can anyone elaborate on the WHY?:confused:
 
You don't have to increase to #1 -- you never have to go larger than the service entrance conductors in dwellings.

Your WHY question is a good one. In the past, others have raised this same question and posed solutions that would focus on leaving the ampacity tables alone but applying a further load diversity factor on dwellings loads. The end result is the same, but it would be nice if a wire always has the same amp limitations whether it be a comercial wire or a dwelling wire.

But I could see some challenges in the code if the service and feeder calculations get a diversity factor applied. You could now have 90 amp loads whereas they were 100 amps loads before. But there are code sections that mandate 100A minimum service to dwellings. This would bump you up to the 310.16 larger wire size regardless of the calculated diverse load, so I don't know how they'd fix that.
 
Can someone tell me when the table 310.15(B)(6) was added to the codebook? I found my old 1987 and 1990 codebooks and it was not in there, I've looked for my 1993 and 1996 books and can't find them. Just curious when it was added and why. After looking at the old codebook, I forgot how much I miss the smaller sized book.
 
Dave,
Look at the "notes to Tables 310-16" in the older code books. I think that it was note 3, but am not sure.
Don
 
If you check manufacturer's catalogs (Southwire's anyway) 2-2-2-4 AL cable is shown rated for 60? (75 AMP) 75? (90 AMP) 90? (100 AMP) and residential (100 AMP)

The notes for "dwelling" indicate the rating is acceptable for services and feeders. Granted a manufacturer's catalog isn't a code book but it seems unlikely to me that a manufacturer would list a wire size for a given rating and use without qualifications if any existed.
 
Uncle Bill

It is 100 amps for residential if the residential installation fits the rule of 310.15(B)(6).
If it is outside this rule then the 75 degree rule applies.
 
I'll ask this question yet again..........BUT WHY??? And I don't want to hear "because the Code says so" I want to know what everyone thinks on their own about this discussion and the discrepencies. I know in reality it may seem petty to be dickering back and forth about a measly 10 amps, but I still just cannot understand the reasoning why the same cable can be used for 90 amps in one situation and 100 in another. The FACTS are that it is the same cable, made from the same material, with the same insulation, so what is the justification to provide 2 different values? It just seems much more complicated than it should be!
 
could be...

could be...

racerdave3 said:
I'll ask this question yet again..........BUT WHY??? And I don't want to hear "because the Code says so" I want to know what everyone thinks on their own about this discussion and the discrepancies. I know in reality it may seem petty to be dickering back and forth about a measly 10 amps, but I still just cannot understand the reasoning why the same cable can be used for 90 amps in one situation and 100 in another. The FACTS are that it is the same cable, made from the same material, with the same insulation, so what is the justification to provide 2 different values? It just seems much more complicated than it should be!
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I may be way off base here but here I go: I think the difference comes from the way the load on the conductor is calculated, there is a difference between a Service/Feeder and a branch circuit. :-?
 
stickboy1375 said:
Why are you so worried about it? just change your ways and be done with it...
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Because this is supposed to be a forum to post questions and LEARN, and that is what I am trying to do here is learn, I think we all are. What good does it do anyone to "just change your ways" if you are doing so blindly?
 
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