# 310.15 (b) 7



## Chris1971 (Dec 27, 2010)

Installing a 100 amp aluminum feeder for a sub panel in a single family home, 2-2-2-4 al cable would be acceptable?


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## user4818 (Jan 15, 2009)

No, must be 1/0 AL.


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## Chris1971 (Dec 27, 2010)

Peter D said:


> No, must be 1/0 AL.



Why?


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## Theriot (Aug 27, 2011)

Now this shouldn't be boring at all. Can't wait to see who wins.


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## user4818 (Jan 15, 2009)

Chris1971 said:


> Why?


SER has to follow the derating rules for NM cable.

Is this cable the primary feeder between the main disconnect and this panel?


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## erics37 (May 7, 2009)

Peter D said:


> SER has to follow the derating rules for NM cable.
> 
> Is this cable the primary feeder between the main disconnect and this panel?


Table 310.15(B)(7) 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

Maybe this makes or breaks it?


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## HARRY304E (Sep 15, 2010)

Peter D said:


> No, must be 1/0 AL.


Wrong....:laughing:

Table 310.15(B)(7)
310.15(B)(7)
(7) 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)(7), 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 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.


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## user4818 (Jan 15, 2009)

Harry, we don't know if this is the primary feeder or not.


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## electricmanscott (Feb 11, 2010)

Who doesn't love selective highlighting!! :laughing:


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## Chris1971 (Dec 27, 2010)

So, 2-2-2-4?


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## Theriot (Aug 27, 2011)

Couldn't he get his answer by posting this as a poll?


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## Chris1971 (Dec 27, 2010)

Feeder from main panel to a sub panel in a single family home.


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## HARRY304E (Sep 15, 2010)

electricmanscott said:


> Who doesn't love selective highlighting!! :laughing:


:laughing::laughing::thumbup:


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## HARRY304E (Sep 15, 2010)

Chris1971 said:


> So, 2-2-2-4?


:yes::yes::yes::thumbup:


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## HARRY304E (Sep 15, 2010)

Peter D said:


> Harry, we don't know if this is the primary feeder or not.


It is a feeder to a sub panel and it will never come close to 80% loaded never mind 100%


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## user4818 (Jan 15, 2009)

Chris1971 said:


> Feeder from main panel to a sub panel in a single family home.



Then it has to be 1/0 AL.


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## user4818 (Jan 15, 2009)

HARRY304E said:


> It is a feeder to a sub panel and it will never come close to 80% loaded never mind 100%


Doesn't matter.


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## Chris1971 (Dec 27, 2010)

Peter D said:


> Then it has to be 1/0 AL.


Why? Please explain.


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## HARRY304E (Sep 15, 2010)

Peter D said:


> Doesn't matter.


Prove why with the proper code article..


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## HARRY304E (Sep 15, 2010)

Peter D said:


> Then it has to be 1/0 AL.


No it doesn't:laughing:


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## erics37 (May 7, 2009)

Peter D said:


> Then it has to be 1/0 AL.


Don't be ambiguous, 480sparky, just state yer s**t clear and simple.

Table 310.15(B)(7) pretty clearly indicates that dwelling feeders are allowed to be sized from there.

EDIT: Nevermind, I see it now. Sorry, I missed it.



> For application of this section,
> the *main power feeder shall be the feeder between the
> main disconnect and the panelboard that supplies, either by
> branch circuits or by feeders, or both, all loads that are part
> or associated with the dwelling unit.*


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## user4818 (Jan 15, 2009)

Chris1971 said:


> Why? Please explain.


The quoted code section only applies if the cable is feeding a panel from the main service disconnect. If it's coming from a main panel and is not the primary dwelling feeder then the cable needs to follow the NM derating rules.


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## user4818 (Jan 15, 2009)

HARRY304E said:


> No it doesn't:laughing:


Are you going to admit you're wrong now?


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## HARRY304E (Sep 15, 2010)

Peter D said:


> The quoted code section only applies if the cable is feeding a panel from the main service disconnect. If it's coming from a main panel and is not the primary dwelling feeder then the cable needs to follow the NM derating rules.





> primary dwelling feeder


And wear are those words in the NEC?:blink:


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## BBQ (Nov 16, 2010)

Chris1971 said:


> Feeder from main panel to a sub panel in a single family home.


Sub panel rules out using the special table, sorry no selective highlighting :laughing:


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## BBQ (Nov 16, 2010)

HARRY304E said:


> And wear are those words in the NEC?:blink:


See post 21


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## Chris1971 (Dec 27, 2010)

BBQ said:


> Sub panel rules out using the special table, sorry no selective highlighting :laughing:


So, 1/0 it is. Sorry everyone as my brain shut down.

No I'm not drinking.:laughing::laughing:


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## user4818 (Jan 15, 2009)

Chris1971 said:


> So, 1/0 it is. Sorry everyone as my brain shut down.
> 
> No I'm not drinking.:laughing::laughing:


You may get this look {:blink:} if you ask for 1/0 AL SER cable at your friendly, local supply counter.


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## erics37 (May 7, 2009)

Peter D said:


> You may get this look {:blink:} if you ask for 1/0 AL SER cable at your friendly, local supply counter.


That's okay, I'd probably say f**k it and just run the #2 cable anyway.


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## user4818 (Jan 15, 2009)

erics37 said:


> That's okay, I'd probably say f**k it and just run the #2 cable anyway.


I'd run the #2 without even a second thought. A dwelling sub panel will never see a full load, and there's a bajillion 100 amp sub panels on #2 Al out there.


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## Chris1971 (Dec 27, 2010)

Peter D said:


> You may get this look {:blink:} if you ask for 1/0 AL SER cable at your friendly, local supply counter.



They stock it. 1200' in stock.:thumbsup:


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## mbednarik (Oct 10, 2011)

or use a 90 amp breaker. Supply houses here stock 1/0 cable.


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## HARRY304E (Sep 15, 2010)

erics37 said:


> Don't be ambiguous, 480sparky, just state yer s**t clear and simple.
> 
> Table 310.15(B)(7) pretty clearly indicates that dwelling feeders are allowed to be sized from there.
> 
> EDIT: Nevermind, I see it now. Sorry, I missed it.


eric where is this located?:blink:

Quote:
For application of this section,
the *main power feeder shall be the feeder between the
main disconnect and the panelboard that supplies, either by
branch circuits or by feeders, or both, all loads that are part
or associated with the dwelling unit.*


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## Chris1971 (Dec 27, 2010)

Peter D said:


> I'd run the #2 without even a second thought. A dwelling sub panel will never see a full load, and there's a bajillion 100 amp sub panels on #2 Al out there.


That's probably fine but, I don't want to get dinged from the inspector.


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## erics37 (May 7, 2009)

HARRY304E said:


> eric where is this located?:blink:


Read Post #7 :laughing:


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## BBQ (Nov 16, 2010)

erics37 said:


> That's okay, I'd probably say f**k it and just run the #2 cable anyway.


The cable will burn ....... Fire and brimstone coming down from the skies! Rivers and seas boiling! Forty years of darkness! Earthquakes, volcanoes... 
Human sacrifice, dogs and cats living together... mass hysteria!


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## erics37 (May 7, 2009)

BBQ said:


> The cable will burn ....... Fire and brimstone coming down from the skies! Rivers and seas boiling! Forty years of darkness! Earthquakes, volcanoes...
> Human sacrifice, dogs and cats living together... mass hysteria!


Pfft, that's only if you believe in god. :laughing:


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## user4818 (Jan 15, 2009)

BBQ said:


> The cable will burn ....... Fire and brimstone coming down from the skies! Rivers and seas boiling! Forty years of darkness! Earthquakes, volcanoes...
> Human sacrifice, dogs and cats living together... mass hysteria!


The same things happen when you run #14 wire in a commercial building.


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## BBQ (Nov 16, 2010)

HARRY304E said:


> eric where is this located?:blink:





erics37 said:


> Read Post #7 :laughing:


:lol::lol::lol:


You can't fake that kind of clueless. :whistling2:


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## Chris1971 (Dec 27, 2010)

Good point. I'll run #2 and put it on a 90 amp circuit.


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## user4818 (Jan 15, 2009)

erics37 said:


> Don't be ambiguous, 480sparky, just state yer s**t clear and simple.
> 
> Table 310.15(B)(7) pretty clearly indicates that dwelling feeders are allowed to be sized from there.
> 
> EDIT: Nevermind, I see it now. Sorry, I missed it.


Never, EVER question my code knowledge ever again! :furious::furious:


































:jester:


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## Chris1971 (Dec 27, 2010)

Peter D said:


> Never, EVER question my code knowledge ever again! :furious::furious:
> 
> 
> 
> ...


I no longer believe your a troll.:laughing::laughing:


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## erics37 (May 7, 2009)

Peter D said:


> Never, EVER question my code knowledge ever again! :furious::furious:
> 
> :jester:


:laughing:

I was wondering when you'd respond to that one! I'm just glad I caught myself before I got all Harry on you.


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## Theriot (Aug 27, 2011)

BBQ said:


> The cable will burn ....... Fire and brimstone coming down from the skies! Rivers and seas boiling! Forty years of darkness! Earthquakes, volcanoes...
> Human sacrifice, dogs and cats living together... mass hysteria!


Is this the prediction of the return of the second coming of Cletis?


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## user4818 (Jan 15, 2009)

erics37 said:


> :laughing:
> 
> I was wondering when you'd respond to that one! I'm just glad I caught myself before I got all Harry on you.


There are two things that one must always avoid when posting - going Harry or going 480sparky in your replies.


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## HARRY304E (Sep 15, 2010)

erics37 said:


> Read Post #7 :laughing:


:laughing:

Duh!..:blink::laughing:

Table 310.15(B)(7)
310.15(B)(7)
(7) 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)(7), 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 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. 


In the blue it does not make it clear that the feeder between the main panel and the sub panel should not be sized by table Table 310.15(B)(7)


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## HARRY304E (Sep 15, 2010)

Peter D said:


> There are two things that one must always avoid when posting - going Harry or going 480sparky in your replies.


:sleep1:


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## user4818 (Jan 15, 2009)

HARRY304E said:


> :sleep1:


I'm going to trademark that and start collecting a fee anytime someone uses it.


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## HARRY304E (Sep 15, 2010)

BBQ said:


> :lol::lol::lol:
> 
> 
> You can't fake that kind of clueless. :whistling2:


Yes when it comes to politics you are clueless.


On another note...:laughing::sleep1:


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## user4818 (Jan 15, 2009)

HARRY304E said:


> Yes when it comes to politics you are clueless.
> 
> 
> On another note....


BBQ is quite a bit liberal in his politics but it's totally wrong to say he's clueless. I think he's very astute even though I mostly disagree with him.


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## erics37 (May 7, 2009)

HARRY304E said:


> In the blue it does not make it clear that the feeder between the main panel and the sub panel should not be sized by table Table 310.15(B)(7)


Well the standard procedure for sizing any feeder would be to use the normal ampacity table 310.15(B)(16)

310.15(B)(7) is an exception for certain dwelling unit service and/or main feeder conductor sizing.

It seems pretty clear to me if you read the whole code section, that it only allows the reduced conductor size for dwelling main power feeders and/or services. When I first looked at it tonight I skimmed over it and missed that important sentence. It's easy to skip stuff in a big block of text like that.


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## BBQ (Nov 16, 2010)

Peter D said:


> BBQ is quite a bit liberal in his politics but it's totally wrong to say he's clueless. I think he's very astute even though I mostly disagree with him.


Well thanks, but no worries we know it's Friday night and that old dog has put a few down. :drink::drink::drink::drink:


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## user4818 (Jan 15, 2009)

BBQ said:


> Well thanks, but no worries we know it's Friday night and that old dog has put a few down. :drink::drink::drink::drink:


True, I keep forgetting that we're well into PWI hours of the night by now. :blink:


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## HARRY304E (Sep 15, 2010)

Peter D said:


> BBQ is quite a bit liberal in his politics but it's totally wrong to say he's clueless. I think he's very astute even though I mostly disagree with him.


He is clueless and will report political posts because he is UN-informed on current events and thinks that politics have no effect on his employment when in fact it does and we are on the very edge of economic collapse 


He is fully Employed there is no problem with the left ruining the economy because after all he is making money at what he is doing for him self and his boss.

I have no doubt in my mind that he is a top dog in the company he is working for.

He wants to ignore the fact that the train is about to hit the brick wall because the Boston Globe says every thing is just fine.

Well I know many Electricians that have not worked full-time in their trade for almost five years because of liberalism..


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## HARRY304E (Sep 15, 2010)

BBQ said:


> Well thanks, but no worries we know it's Friday night and that old dog has put a few down. :drink::drink::drink::drink:


I'm still waiting for peters recommendation...


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## user4818 (Jan 15, 2009)

HARRY304E said:


> I'm still waiting for peters recommendation...


Can't help you there, I don't drink. 

Unless you're talking CocaCola or Powerade. Those are my favorites :laughing:


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## Dennis Alwon (May 9, 2009)

This is quite simple but their are a few things that are being overlooked.

1) Is this the main feeder-- in other words, does this feeder carry the entire load of the dwelling? If not then it cannot use 310.15(B)(7).

2) Since this is the 2011 NEC being quoted then SE cable can be used at 75C if the se cable is not installed in thermal insulation. If no insulation then it can be protected at 90 amps since that is the 75C rating of the #2 aluminum. 

3) #1 aluminum can be used for 100 amps again if it is not installed in thermal insulation.


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## user4818 (Jan 15, 2009)

HARRY304E said:


> He is clueless and will report political posts because he is UN-informed on current events and thinks that politics have no effect on his employment when in fact it does and we are on the very edge of economic collapse
> 
> 
> He is fully Employed there is no problem with the left ruining the economy because after all he is making money at what he is doing for him self and his boss.
> ...


I don't know his views on that, but I agree that the economy is poised for a major collapse. If that happens we'll all be in the same boat, unfortunately.


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## HARRY304E (Sep 15, 2010)

erics37 said:


> Well the standard procedure for sizing any feeder would be to use the normal ampacity table 310.15(B)(16)
> 
> 310.15(B)(7) is an exception for certain dwelling unit service and/or main feeder conductor sizing.
> 
> It seems pretty clear to me if you read the whole code section, that it only allows the reduced conductor size for dwelling main power feeders and/or services. When I first looked at it tonight I skimmed over it and missed that important sentence. It's easy to skip stuff in a big block of text like that.


I agree that ,That section is poorly written


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## HARRY304E (Sep 15, 2010)

Peter D said:


> Can't help you there, I don't drink.
> 
> Unless you're talking CocaCola or Powerade. Those are my favorites :laughing:



I respect that.....:thumbup::laughing:


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## Dennis Alwon (May 9, 2009)

This article is one of the most misunderstood articles in the NEC. IMO, it is pretty clear in most cases.


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## HARRY304E (Sep 15, 2010)

Peter D said:


> BBQ is quite a bit liberal in his politics but it's totally wrong to say he's clueless. I think he's very astute even though I mostly disagree with him.


Well I will leave the politics for another day.

We should join the Plumbing Zone politics are allowed there.

http://www.plumbingzone.com/f13/random-political-thoughts-thread-15949/


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## HARRY304E (Sep 15, 2010)

Dennis Alwon said:


> This article is one of the most misunderstood articles in the NEC. IMO, it is pretty clear in most cases.


I do not see a good reason to have Table 310.15(B)(7) If you cannot use it to feed a sub panel in almost all cases it will not be loaded even at 80% full load current.


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## Dennis Alwon (May 9, 2009)

HARRY304E said:


> I do not see a good reason to have Table 310.15(B)(7) If you cannot use it to feed a sub panel in almost all cases it will not be loaded even at 80% full load current.



There have been proposals to do away with it. If the panel will not be filled to 80% then just use a smaller breaker. What's the big deal. The residential loads are based on the diversity of the loads in a dwelling. When you do not have the entire load of the dwelling on the feeder then the diversity can get messed up.

Suppose I have a sub panel and put all my heat pumps and heat strips in it. That is a very different diversity then the way a home would be diversified under normal conditions. The sub panel in that case is not diversified at all. So how can you control what loads go where. That is why the rule is the way it is.


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## HARRY304E (Sep 15, 2010)

Dennis Alwon said:


> There have been proposals to do away with it. If the panel will not be filled to 80% then just use a smaller breaker. What's the big deal. The residential loads are based on the diversity of the loads in a dwelling. When you do not have the entire load of the dwelling on the feeder then the diversity can get messed up.
> 
> Suppose I have a sub panel and put all my heat pumps and heat strips in it. That is a very different diversity then the way a home would be diversified under normal conditions. The sub panel in that case is not diversified at all. So how can you control what loads go where. That is why the rule is the way it is.


Very good point ,And in that case the load will be high and a load calculation would come in handy for The sub panel.


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## erics37 (May 7, 2009)

HARRY304E said:


> Very good point ,And in that case the load will be high and a load calculation would come in handy for The sub panel.


A load calculation is prudent for any panel.


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## HARRY304E (Sep 15, 2010)

erics37 said:


> A load calculation is prudent for any panel.


That is correct and we can avoid this issue with this section of the code


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## Roger123 (Sep 23, 2007)

HARRY304E said:


> :laughing:
> 
> Duh!..:blink::laughing:
> 
> ...


Here Harry, I fixed it for you, I made all the blue words black again, so it can be easier to understand!


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## HARRY304E (Sep 15, 2010)

Roger123 said:


> Here Harry, I fixed it for you, I made all the blue words black again, so it can be easier to understand!


Table 310.15(B)(7)
310.15(B)(7)
(7) 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)(7), 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 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. 


Okay I'll make it green either way that is a source of confusion.:blink:


For application of this section,
 the main power feeder shall be the feeder between the
 main disconnect and the panelboard that supplies, either by
  branch circuits or by feeders, or both, all loads that are part
 or associated with the dwelling unit.

In blue is the source..:blink:


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## BBQ (Nov 16, 2010)

HARRY304E said:


> I agree that ,That section is poorly written


Actually it was just dumbed down recently so even guys like you could understand it. :thumbsup:


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## Davethewave (Jan 6, 2012)

Dennis Alwon said:


> This is quite simple but their are a few things that are being overlooked.
> 
> 1) Is this the main feeder-- in other words, does this feeder carry the entire load of the dwelling? If not then it cannot use 310.15(B)(7).
> 
> ...


Thank you! Wondering why everything kept jumping from #2 to 1/0. Always use #1 for 100 amp.


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## jp8302 (May 25, 2012)

feeder and sub panel emply that it is not a service conductor therefore not applicable to table 310.15(b)(6) 
so use310.16 75'c column use #1 or 1/0 al with #6 al ground


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## BBQ (Nov 16, 2010)

jp8302 said:


> feeder and sub panel emply that it is not a service conductor therefore not applicable to table 310.15(b)(6)
> so use310.16 75'c column use #1 or 1/0 al with #6 al ground


That table can apply to any feeder that carries the full load of a dwelling unit.

Welcome to the forum but you are going to have a tough ride if you just keep posting your opinion without code facts to back it up. :laughing:



> (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
> ...


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## jp8302 (May 25, 2012)

May have shot myself in the foot there, sorry, proves you cant take ahj's word as gospel if your in a code debate. checking the good book now while eating my crow


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## jp8302 (May 25, 2012)

310.15 (b)7 sizes conductors carrying 100% of load to a dwelling, no other feeder shall be required to be sized over this. If you have a 200amp panel board with an auxilary 100amp down stream the 100 wpould be sized by 310.16, the 200 310.15(b)7 if it was (2) 100 amp panels one would not be required to be sized #1 if the supply is #2al

I apologize if i mis spoke, need to do my book work after inspector man quotes something


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## erics37 (May 7, 2009)

jp8302 said:


> 310.15 (b)7 sizes conductors carrying 100% of load to a dwelling, no other feeder shall be required to be sized over this. If you have a 200amp panel board with an auxilary 100amp down stream the 100 wpould be sized by 310.16, the 200 310.15(b)7 if it was (2) 100 amp panels one would not be required to be sized #1 if the supply is #2al
> 
> I apologize if i mis spoke, need to do my book work after inspector man quotes something


Just going on record reminding ya that the table formerly known as 310.16 is now 310.15(B)(16).

Don't worry, it'll take me 3 or 4 code cycles to remember that too :blink:


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