# sub panel wiring size?



## smkie (Feb 11, 2010)

So a guy i know and I were debating back and forth of on the size wire for a 100 A sp i told him you have to you use the 75 celsius colum on 310.16 which would be 3 AWG copper or a 1 AWG, he said " i could use 310.15(B)(6) which is would be 2 AWG alum. or 4 AWG copper. Who is right?


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## BEAMEUP (Sep 19, 2008)

smkie said:


> So a guy i know and I were debating back and forth of on the size wire for a 100 A sp i told him you have to you use the 75 celsius colum on 310.16 which would be 3 AWG copper or a 1 AWG, he said " i could use 310.15(B)(6) which is would be 2 AWG alum. or 4 AWG copper. Who is right?


Your both right, If it was for anything other than a dwelling , you are right, If it is for a dwelling he is right.


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## electricmanscott (Feb 11, 2010)

This is not correct....


BEAMEUP said:


> Your both right, If it was for anything other than a dwelling , you are right, If it is for a dwelling he is right.



310.15 B 6 Applies ONLY IF the feeder is supplying the load to the entire dwelling. Otherwise there are other factors that come into play.

I don't quite understand why this one is so difficult but it sure seems that it is. Probably a top 10 violation I see on a regular basis. In fact on job I am working on now the last guy in, just a few months ago, incorrectly used 310.15 B 6 to size a panel feeder. I will be pointing this out when I have the inspector in for my work.


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## BEAMEUP (Sep 19, 2008)

electricmanscott said:


> This is not correct....
> 
> 
> 
> 310.15 B 6 Applies ONLY IF the feeder is supplying the load to the _*entire*_ dwelling. Otherwise there are other factors that come into play.


Show me in the code book the word ENTIRE.


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## electricmanscott (Feb 11, 2010)

BEAMEUP said:


> Show me in the code book the word ENTIRE.


Since I did not quote the section the actual word entire may not be there. I suggest you read 310.15 B 6. You'll see it says "all loads". That IS a direct quote. You can not use that table to size a "sub panel" No sub panel isn't in their either.


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## John Valdes (May 17, 2007)

310.15 does say feeders and services. But if I used 310.15 to size wire for a sub panel I would be re-pulling the feeder.
Great question, and I look forward to hearing from the others, as I always use 310.16 for subs.


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## electricmanscott (Feb 11, 2010)

John Valdes said:


> 310.15 does say feeders and services. But if I used 310.15 to size wire for a sub panel I would be re-pulling the feeder.
> Great question, and I look forward to hearing from the others, as I always use 310.16 for subs.


Did you read what it says? Does anybody read what it says?


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## Dennis Alwon (May 9, 2009)

BEAMEUP said:


> Show me in the code book the word ENTIRE.


You are correct in that the word "entire" is not there, however Scott is saying that the feeder must be the main power feeder in order to use 310.15(B)(6).

It goes on to state...


> 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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## BEAMEUP (Sep 19, 2008)

electricmanscott said:


> Since I did not quote the section the actual word entire may not be there. I suggest you read 310.15 B 6. You'll see it says "all loads". That IS a direct quote. You can not use that table to size a "sub panel" No sub panel isn't in their either.


After re-reading that section I can see both sides of the argument. Let me give an example of my thinking. Lets say you have a 400 amp service for a single family home, the service is on the side of the house by the garage. I have one run out of the meter to a 200 amp MB panel in the garage. The other run out of the meter goes into a 200amp disconnect next to the MB panel. Out of the disconnet I run 4/0 SER AL to a 200 amp sub panel on the 2nd floor.

In this case I can use 310.15 (b)6 to size the feeder to the sub panel on the 2nd floor. It does not serve the entire load of the house. There is a new sentence in this section that states "that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit."

Now lets go one step futher, I run a 100amp sub panel off the 200 amp sub panel on the 2nd floor, I can still use 310.15 (b)6 to size that run of SER as well.

That sentence I quoted in this post says circuits or feeders, not a single circuit or a single feeder, it plurl as in mutible as long as it is associated with that home I'm code compliant.


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## NolaTigaBait (Oct 19, 2008)

THis is such a stupid rule. #4 is ok if its the main power feeder, but if you run a 2nd panel off that main feed, I need to use #3....Doesn't make much sense to me.


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## Dennis Alwon (May 9, 2009)

BEAMEUP said:


> In this case I can use 310.15 (b)6 to size the feeder to the sub panel on the 2nd floor. It does not serve the entire load of the house.] I agree but only because the garage is not part of the dwelling.
> 
> 
> 
> ...


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## Speedy Petey (Jan 10, 2007)

NolaTigaBait said:


> THis is such a stupid rule. #4 is ok if its the main power feeder, but if you run a 2nd panel off that main feed, I need to use #3....Doesn't make much sense to me.


I 100% agree, and have YET to hear ANY valid argument against it.


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## Speedy Petey (Jan 10, 2007)

electricmanscott said:


> In fact on job I am working on now the last guy in, just a few months ago, incorrectly used 310.15 B 6 to size a panel feeder. I will be pointing this out when I have the inspector in for my work.


Now WHY would you do this??? Will you feel better after reporting this "serious" violation? 

IMO is it NOT a violation as this section is not as cut and dry as you make it out to be. This is QUITE open to interpretation, as many of the posts here show.

I have always used 310.15(B)(6) for sub feeders in a dwelling and will continue to do so.


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## NolaTigaBait (Oct 19, 2008)

> I have always used 310.15(B)(6) for sub feeders in a dwelling and will continue to do so.


Me too. Glad to hear I'm not alone on this!


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## BEAMEUP (Sep 19, 2008)

Well weather I'm right or wrong, I have never been called on this in the state of Washington and have had this very example go thru plan review and get signed off. Now it can be likely that the inspectors in the state of Washington and all of the places I have done this are miss understanding the code, but the inspectors are passing it this way. So who knows. I have been wrong before & I guarantee that I'll be wrong again, but it's passing inspections


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## BuzzKill (Oct 27, 2008)

NolaTigaBait said:


> Me too. Glad to hear I'm not alone on this!


 yeah thast would be the wis thing to do I think


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## B4T (Feb 10, 2009)

These CMP guys need to slow down making code changes and try using it in the real world like the rest of us. :no:


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## jwjrw (Jan 14, 2010)

BEAMEUP said:


> After re-reading that section I can see both sides of the argument. Let me give an example of my thinking. Lets say you have a 400 amp service for a single family home, the service is on the side of the house by the garage. I have one run out of the meter to a 200 amp MB panel in the garage. The other run out of the meter goes into a 200amp disconnect next to the MB panel. Out of the disconnet I run 4/0 SER AL to a 200 amp sub panel on the 2nd floor.
> 
> In this case I can use 310.15 (b)6 to size the feeder to the sub panel on the 2nd floor. It does not serve the entire load of the house. There is a new sentence in this section that states "that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit."
> 
> ...


 

In 2008 you now have to use the 60 column with SER cable here so you couldn't use 4/0.


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## Dennis Alwon (May 9, 2009)

Speedy Petey said:


> I 100% agree, and have YET to hear ANY valid argument against it.


Pete the argument is this. The reason we are allowed to use T.310.15(B)(6) for dwellings is because of the diversity of the loads in a residence. When you add sub panels you are changing the diversity of the load. For instance, if the sub panel only had loads for heating, a/c, etc then the diversity that exists for dwellings is no longer there. 

In reality, I agree with you that problems will probably never arise from this and perhaps it should be re written. I am not arguing that at all but I agree with Scotts interpretation of the rule as written. 

There now you have the reason for the rule- it will not change anything for you but at least you know why. For me, I prefer to wire it by the code to keep my ass out of potential problems.


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## waco (Dec 10, 2007)

I fail to see the issue. Paragraph 310.15 (B) (6) isn't very well written, but the part that says, "...that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit" only serves to confirm the applicability of Table 310(B)(6) which would appear to be "dwellings" without reservation or exception.


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## Dennis Alwon (May 9, 2009)

jwjrw said:


> In 2008 you now have to use the 60 column with SER cable here so you couldn't use 4/0.


IMO, the use of SER does not enter into the equation if T. 310.15(B)(6) is applicable.


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## electricmanscott (Feb 11, 2010)

Speedy Petey said:


> Now WHY would you do this??? Will you feel better after reporting this "serious" violation?
> 
> IMO is it NOT a violation as this section is not as cut and dry as you make it out to be. This is QUITE open to interpretation, as many of the posts here show.
> 
> I have always used 310.15(B)(6) for sub feeders in a dwelling and will continue to do so.


Just because you are wrong, and without question you are wrong, and don't give a crap I should look the other way? I have to bid against guys like you. I bid a code compliant job for what it should cost and you bid a corner cutting illegal job for cheap. You bet your ass I am going to drop a dime. This may not be a _serious_ viloation but make no mistake, it is a violation. If it were something like receptacles spaced over 12 feet or something like that I'd ignore it but it isn't. 310.15 B 6 is not allowable in this case and further more it is se cable installed in insulation. (another cable size violation for those not up on the NEC)

To add to this I am paying for inspections that should keep everybody on a level playing field. I am going to call out the contractor, I know who it is, and if it was inspected I am going to call out the inspector.


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## NolaTigaBait (Oct 19, 2008)

:sleep1:


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## electricmanscott (Feb 11, 2010)

NolaTigaBait said:


> :sleep1:


I don't get it. Is that you sleeping in front of your code book instead of reading it?


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## B4T (Feb 10, 2009)

electricmanscott said:


> I don't get it. Is that you sleeping in front of your code book instead of reading it?


I think Nola is saying he doesn't agree with your rant and I don't either.

IMO dropping a dime on another EC over a petty thing like this only makes YOU look bad.

Saying you would turn in the inspector is really going off the deep end IMO. 

I would call up the other EC and ask him how he came up with that wire size if it bothered me that much.

I lose jobs all the time to unlicensed firemen who moonlight as electricians because they have "buddies" who need work done.

So goes the EC business and about it only makes you bitter IMO.


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## jwjrw (Jan 14, 2010)

Dennis Alwon said:


> IMO, the use of SER does not enter into the equation if T. 310.15(B)(6) is applicable.


 
The op stated he left the disconnect with 4/0 ser. So in my mind he cant use the 75deg column. If he was going to the disconnect then I say he would be ok. Just my opinion.


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## Speedy Petey (Jan 10, 2007)

electricmanscott said:


> Just because you are wrong, and without question you are wrong, and don't give a crap I should look the other way? I have to bid against guys like you. ..........


Guys like me??? Don't pull this holier than thou bull sh*t with me. 
I do wire to the code, and without question I am NOT "wrong" in this, and I do happen to give a crap. I am using an interpretation of the code that ALL my local fellow electricians and inspectors agree with, so I am on a completely level playing field with my peers.


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## electricmanscott (Feb 11, 2010)

Speedy Petey said:


> Guys like me??? Don't pull this holier than thou bull sh*t with me.
> I do wire to the code, and without question I am NOT "wrong" in this, and I do happen to give a crap. I am using an interpretation of the code that ALL my local fellow electricians and inspectors agree with, so I am on a completely level playing filed with my peers.


I stand behind everything I said 100 percent. You are wrong.


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## electricmanscott (Feb 11, 2010)

Black4Truck said:


> I think Nola is saying he doesn't agree with your rant and I don't either.
> 
> IMO dropping a dime on another EC over a petty thing like this only makes YOU look bad.
> 
> ...


You are entitled to your opinion and you can do things how you see fit. But your way is not the only way.


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## electricmanscott (Feb 11, 2010)

I don't see what you guys are using to validate your arguments. Actually none of you have offered ANYTHING other than "we always do it this way" and "it passes inspection" and "look at my goofy smiley face". All mean nothing.


I offer the actual wording of 310.15 B 6 as my argument.


To add to that I'll throw in the handbook commentary.

_Section 310.15(B)(6) permits the main feeder to a dwelling unit to be sized according to table 310.15(B)(6). For the 2008 code the panel clarified that this permission to use this table applies only to conductors carrying 100 percent of the dwelling units diversified load_.


Counter point?


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## Dennis Alwon (May 9, 2009)

jwjrw said:


> The op stated he left the disconnect with 4/0 ser. So in my mind he cant use the 75deg column. If he was going to the disconnect then I say he would be ok. Just my opinion.


Here is where interpretation gets sticky and I cannot say that you are wrong or that I am right. I would like to explain further.

T. 310.15(B)(6) has a list of conductors and cables that satisfy its use. For instance in no way may you use romex to any panel and be able to use this table. SE cable , however, is listed in the header.

Now If you carry the total load of the dwelling, ie, you leave a meter and go to a main disco and then feed an interior panel with ser cable, then I contend that 4/0 is okay based on T. 310.15(B)(6). Nowhere in this table does it refer to ser being used as a feeder. I realize article 338 does mention ser as a feeder but in this situation I believe t.310.15(B)(6) trumps article 338. 

I do believe that the CMP (code making panel) may have overlooked this section and I would bet it is being worked on in 2011 code. But as I read it today-- 4/0 is okay if it carries the entire load of the panel.


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## Dennis Alwon (May 9, 2009)

I totally agree with Scott's interpretation of this article and if you use the 2008 NEC I think it is pretty clear.


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## Speedy Petey (Jan 10, 2007)

electricmanscott said:


> I stand behind everything I said 100 percent.


So do I.



electricmanscott said:


> You are wrong.


And with this statement you prove your arrogance.


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## Speedy Petey (Jan 10, 2007)

Dennis Alwon said:


> ......and if you use the 2008 NEC I think it is pretty clear.


Here is one key factor. We do not use the 2008 NEC. Not everyone does.


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## Dennis Alwon (May 9, 2009)

Speedy Petey said:


> Here is one key factor. We do not use the 2008 NEC. Not everyone does.


I know, that is why I wrote that.  Nobody seemed to have mentioned it so I thought I would. Even with the older NEC I believe the intent was there but it was not as clear.


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## NolaTigaBait (Oct 19, 2008)

electricmanscott said:


> I don't get it. Is that you sleeping in front of your code book instead of reading it?


:laughing:That was good. But seriously, I don't get it. Can you make a compelling reason not to do it, other than it "2008" code? I know Dennis mentioned something about diversity, but in reality how often does this happen? If I have a 200 amp main lug meter/panel combo. I feed the line side with 2/0. Then I run all electric appliance out of that panel, everything is ok. But, If I want to add a 100 amp mlo panel in the house, I have to use #2 copper(NM) IF the load doesn;t exceed 95 amps! And 1/0 if I want to use aluminum...I'm just talking about practicality....I think it;s dumb and I understand how it is written. This has been around here for years and I've never seen a problem from using the 310.15b6 for feeders.


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## Dennis Alwon (May 9, 2009)

NolaTigaBait said:


> I think it;s dumb and I understand how it is written. This has been around here for years and I've never seen a problem from using the 310.15b6 for feeders.


That is because the code is the minimum but even at that there is room for error. I guess the CMP knows they are working with people who will try and get by with anything.

Many things in the code are "dumb" in some respects, but it is what it is. I don't agree with all of it but I do try and keep things legit. Am I perfect? By no means but I do try.

I have seen Nm cable used underground to a shed and it was there for 20 years or more without an issue until we dug it up. That does not mean I will use nm cable for underground feeders. In another soil, etc it may not last.

Diversity is based on the type of loads that are in a dwelling. That diversity gets changed every time we add a panel. I will grant it that an outdoor panel feeding an indoor panel and an a/c load should not change the diversity to warrant a larger conductor. In fact, I believe that is one of the proposed changes for this section.


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## John Valdes (May 17, 2007)

Is it possible that the the words "120/240-Volt, 3-Wire" have anything to do with it?
3 Wire?

We run 4 wire feeders now.


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## Dennis Alwon (May 9, 2009)

John Valdes said:


> Is it possible that the the words "120/240-Volt, 3-Wire" have anything to do with it?
> 3 Wire?
> 
> We run 4 wire feeders now.


I believe that is in reference to the service. Thus if you have a dwelling where it is fed from a 3 phase system (there are some) then these rules do not apply even tho it is a dwelling.


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## electricmanscott (Feb 11, 2010)

Speedy Petey said:


> And with this statement you prove your arrogance.


And with your complete lack of anything remotely resembling a legitimate argument in your favor you prove your ignorance. 

I am still waiting for you guys that insist I am wrong to show me even a hint of how that is.

No, saying the code rule is stupid doesn't count.


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## JohnSham (Jan 7, 2010)

*code*

I fully agree with Scott. It seems clear, although, stupid. We follow code to the T here in Montana. 

John


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## Dennis Alwon (May 9, 2009)

electricmanscott said:


> And with your complete lack of anything remotely resembling a legitimate argument in your favor you prove your ignorance.
> 
> I am still waiting for you guys that insist I am wrong to show me even a hint of how that is.
> 
> No, saying the code rule is stupid doesn't count.


Be careful Scott, Marc may banish you back to Mike Holt's playground. :laughing:


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## Speedy Petey (Jan 10, 2007)

JohnSham said:


> We follow code to the T here in Montana.


So do we. :thumbsup:


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## electricmanscott (Feb 11, 2010)

Dennis Alwon said:


> Be careful Scott, Marc may banish you back to Mike Holt's playground. :laughing:


Are you suggesting that's a bad thing? :jester: :sneaky2:


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## jwjrw (Jan 14, 2010)

Dennis Alwon said:


> Here is where interpretation gets sticky and I cannot say that you are wrong or that I am right. I would like to explain further.
> 
> T. 310.15(B)(6) has a list of conductors and cables that satisfy its use. For instance in no way may you use romex to any panel and be able to use this table. SE cable , however, is listed in the header.
> 
> ...


 
I also am not saying Im right and you are not. The issue to me is once you leave a main disconnect which is fed by a 3wire you must run a 4wire to the now Subpanel. Maybe Im wrong and the inside panel is not a subpanel but it is not a service panel because the main is not in it. I read 310.15 b6 to apply to 3wire feeders and not 4wire ser. I guess I better ask my ahj how they see it when I get in that situation.


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## Dennis Alwon (May 9, 2009)

jwjrw said:


> I also am not saying Im right and you are not. The issue to me is once you leave a main disconnect which is fed by a 3wire you must run a 4wire to the now Subpanel. Maybe Im wrong and the inside panel is not a subpanel but it is not a service panel because the main is not in it. I read 310.15 b6 to apply to 3wire feeders and not 4wire ser. I guess I better ask my ahj how they see it when I get in that situation.



Think about this. The main panel is the service panel all other panels are feed either directly or indirectly from the main distribution panel. Now how can you have a 3 wire feeder for a panel.


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## jwjrw (Jan 14, 2010)

Dennis Alwon said:


> Think about this. The main panel is the service panel all other panels are feed either directly or indirectly from the main distribution panel. Now how can you have a 3 wire feeder for a panel.


 
You cant. And that was my point. I agree the wording seems to say both. I hope they clear it up in 2011.


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## Dennis Alwon (May 9, 2009)

jwjrw said:


> You cant. And that was my point. I agree the wording seems to say both. I hope they clear it up in 2011.


I am not saying the wording is poor. In fact, I am saying the fact that the articles speaks of feeders means that a 4 wire may be used as long as it carries the entire load of the service.

Meter to first disconnect or panel is service entrance conductors. First disconnect or panel to the next panel is a feeder even if all the breakers, except the main, for the dwelling are in this panel.

The title of section 6 is service entrance and feeders but only for dwellings that are fed with a 120/240. 3 wire service. Three phase is out even if it is a dwelling.


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## jwjrw (Jan 14, 2010)

Dennis Alwon said:


> I am not saying the wording is poor. In fact, I am saying the fact that the articles speaks of feeders means that a 4 wire may be used as long as it carries the entire load of the service.
> 
> Meter to first disconnect or panel is service entrance conductors. First disconnect or panel to the next panel is a feeder even if all the breakers, except the main, for the dwelling are in this panel.
> 
> The title of section 6 is service entrance and feeders but only for dwellings that are fed with a 120/240. 3 wire service. Three phase is out even if it is a dwelling.


Im saying the wording isnt clear. If you read the first part it says fed with a three wire. That indicates to me they are referring to the line side of the service. Then it goes on to mention feeders which would mean a 4wire. I can see both sides of the coin on this. Its another one of those times when I wish the code was worded for idiots like me in plain simple english!


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## Dennis Alwon (May 9, 2009)

jwjrw said:


> Im saying the wording isnt clear. If you read the first part it says fed with a three wire. That indicates to me they are referring to the line side of the service. Then it goes on to mention feeders which would mean a 4wire. I can see both sides of the coin on this. Its another one of those times when I wish the code was worded for idiots like me in plain simple english!


The reference to 3 wire is that the service conductors must originate from a 3 wire 120/240 single phase service. All the other methods, ie, laterals and feeders must also originate from a 3 wire service that is 120/240. It does not state a 3 wire feeder. You are reading way too much into this.


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## electricmanscott (Feb 11, 2010)

Dennis Alwon said:


> The reference to 3 wire is that the service conductors must originate from a 3 wire 120/240 single phase service. All the other methods, ie, laterals and feeders must also originate from a 3 wire service that is 120/240. It does not state a 3 wire feeder. You are reading way too much into this.


I have no idea what he is getting at. :001_huh:


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## Dennis Alwon (May 9, 2009)

electricmanscott said:


> I have no idea what he is getting at. :001_huh:


I think he thinks the 3 wire reference conflicts with a feeder needing 4 wires. I don't see it that way at all.


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## jwjrw (Jan 14, 2010)

Dennis Alwon said:


> I think he thinks the 3 wire reference conflicts with a feeder needing 4 wires. I don't see it that way at all.


 
It does say 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. It does not say 3 or 4 wire. Im not saying Im right just that thats how I read it.


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## Dennis Alwon (May 9, 2009)

jwjrw said:


> It does say 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. It does not say 3 or 4 wire. Im not saying Im right just that thats how I read it.


The 120/240v 3 wire is in reference to the service. How can you have a 4 wire single phase service? If it read 120/240 Volt 3 or 4 wire, single phase service conductors that would make no sense.


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## jwjrw (Jan 14, 2010)

Dennis Alwon said:


> The 120/240v 3 wire is in reference to the service. How can you have a 4 wire single phase service? If it read 120/240 Volt 3 or 4 wire, single phase service conductors that would make no sense.


And since they are talking about the service I believe they are referring to the line side and not the load. I dont pretend to know or understand the code as well as you so maybe I am not correct. I do learn alot for many of you guys so here you go dennis another thanks!:thumbsup: Oops wrong neighborhood!:laughing:


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