# 2/3 romex



## Magnettica (Jan 23, 2007)

Any idea how much per foot 2/3 romex is going for these days? Guy wants a price on a 2 family service with remote MLO panels in copper. I can't use 4/3 for 100 amp mains can I?


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## MDShunk (Jan 7, 2007)

It's been a long time since I've used romex in a gauge that large. It's even been a good while since I've used copper SER. Sorry, guess I'm no help.


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## Magnettica (Jan 23, 2007)

MDShunk said:


> It's been a long time since I've used romex in a gauge that large. It's even been a good while since I've used copper SER. Sorry, guess I'm no help.


Your PM box is full too. :laughing:


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## r_merc (Jul 5, 2008)

Last time I used 2/3 it was $5.34 a foot


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## Mike Guile (Jan 14, 2010)

*Cu*

Yeah, it's about 5.75 ft here. I think it's good for a 100 amp residental service by chart I just looked at. It's close either way.


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## oldman (Mar 30, 2007)

$650/125' at cooper


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## Dennis Alwon (May 9, 2009)

Magnettica said:


> Any idea how much per foot 2/3 romex is going for these days? Guy wants a price on a 2 family service with remote MLO panels in copper. I can't use 4/3 for 100 amp mains can I?


Can you install a 90 amp breaker and use 4/3 NM? That would save some cost. You can use a 90 amp breaker as long as the calculated load is 85 amps or less.


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## MDShunk (Jan 7, 2007)

Dennis Alwon said:


> Can you install a 90 amp breaker and use 4/3 NM? That would save some cost. You can use a 90 amp breaker as long as the calculated load is 85 amps or less.


I usually do my MLO panels, with outdoor disconnects, by robbing the 100 or 200 amp breaker out of a MB panel to put in the empty outdoor disco can and putting lugs in the MB panel to make it an MLO panel. That saves a ton of money over buying a MLO panel and a seperate 90 or 100 amp breaker for the outdoor disconnect. Perhaps enough to offset the cost of going from #4 to #2 or 3


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## oldman (Mar 30, 2007)

4/3 is $3.50/ft


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## Magnettica (Jan 23, 2007)

I have two main disconnects on the exterior so the 2/3 is for the feeders to the MLO panels. This is commonly referred to as the grey area for table 310.15(B)(6).


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## MDShunk (Jan 7, 2007)

Magnettica said:


> I have two main disconnects on the exterior so the 2/3 is for the feeders to the MLO panels. This is commonly referred to as the grey area for table 310.15(B)(6).


If it's after a breaker, it's a branch circuit. I really don't see a grey area.


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## Magnettica (Jan 23, 2007)

Dennis Alwon said:


> Can you install a 90 amp breaker and use 4/3 NM? That would save some cost. You can use a 90 amp breaker as long as the calculated load is 85 amps or less.


That's what I wanted to do then the guy wanted to make sure it was good for an A/C condenser later on. I have no idea how many tons the A/C might be so I would like to install a true 100 amps.


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## Magnettica (Jan 23, 2007)

MDShunk said:


> If it's after a breaker, it's a branch circuit. I really don't see a grey area.


It's after the main disconnect.


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## Mike Guile (Jan 14, 2010)

*try this*

http://www.cerrowire.com/default.aspx?id=3046

and this I found. Wrong size but ...

IMO he could use table 310.15(B)(6) if he uses SER. That would mean he could use #2 copper ser cable. Article 338 for SE (service entrance) cable refers you to 334 which is the article for nm-b. However it refers you there for interior installation when the SE cable is not being used as a main power feeder. If it is used other than a main power feeder then its ampacity would be restricted to that of nm-b and the 60C column of table 310.16. However unlike nm-b the conductors in SER are identified as thhn or thwn or thwn-2 which allows it to use 310.15 (B)(6) for main power feeders. So a #2 copper SER cable is good for 125 amps when installed as a main power feeder.


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## Dennis Alwon (May 9, 2009)

MDShunk said:


> If it's after a breaker, it's a branch circuit. I really don't see a grey area.


I don't see a gray area either but I don't agree with your statement. If I run a cable from a main panel to a sub panel that cable is after a breaker and it is still a feeder. A branch circuit is the feed after the last OCPD in the circuit.

Maybe I am missing something because I am sure you know this fact.


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## waco (Dec 10, 2007)

I use 2-2-2-4 AL SER "donkey d**k" for feeders to subs or four #4 CU THHN in conduit. Bet I'm wrong, but then again, I'm getting old....

I thought NM (isn't that what Romex is) couldn't be used for services and feeders....


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## Magnettica (Jan 23, 2007)

Didn't you guys used to go back and forth on the Mike Holt forum for years on wether or not table 310.15 (B)(6) could be used for this scenario? Maybe it was for detached garage feeders.


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## Dennis Alwon (May 9, 2009)

Mike Guile said:


> http://www.cerrowire.com/default.aspx?id=3046
> 
> and this I found. Wrong size but ...
> 
> IMO he could use table 310.15(B)(6) if he uses SER. That would mean he could use #2 copper ser cable. Article 338 for SE (service entrance) cable refers you to 334 which is the article for nm-b. However it refers you there for interior installation when the SE cable is not being used as a main power feeder. If it is used other than a main power feeder then its ampacity would be restricted to that of nm-b and the 60C column of table 310.16. However unlike nm-b the conductors in SER are identified as thhn or thwn or thwn-2 which allows it to use 310.15 (B)(6) for main power feeders. So a #2 copper SER cable is good for 125 amps when installed as a main power feeder.


Even if it isn't the main power feed he could use #2 with a 100 amp breaker by using T. 310.16 as long as the calculated load is 95 amps or less.

The fact that SE cable marks the conductors or not has no play in the equation. T. 310.15.(B)(6) is allowed for SE cable as long as that feeder carries the entire load of the dwelling. I don't see where the conductor label has anything to do with it.


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## user4818 (Jan 15, 2009)

MDShunk said:


> I usually do my MLO panels, with outdoor disconnects, by robbing the 100 or 200 amp breaker out of a MB panel to put in the empty outdoor disco can and putting lugs in the MB panel to make it an MLO panel. That saves a ton of money over buying a MLO panel and a seperate 90 or 100 amp breaker for the outdoor disconnect. Perhaps enough to offset the cost of going from #4 to #2 or 3


What brand do you typically do this with?


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## B4T (Feb 10, 2009)

*I see this as saying #4 cu. is all he needs..


Table 310.15(B)(6) 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
Conductor (AWG or kcmil)
Service or Feeder
Rating (Amperes) Copper
Aluminum or
Copper-Clad
Aluminum​*100 4 2
110 3 1
125 2 1/0
150 1 2/0
175 1/0 3/0
200 2/0 4/0
225 3/0 250
250 4/0 300
300 250 350
350 350 500​400 400 600


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## waco (Dec 10, 2007)

Interesting bit of wit here....

http://dbs.idaho.gov/electrical/Newsbriefs/1.13_SerCable.pdf


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## Magnettica (Jan 23, 2007)

waco said:


> Interesting bit of wit here....
> 
> http://dbs.idaho.gov/electrical/Newsbriefs/1.13_SerCable.pdf


Yup, that's it. That's the controversy.


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## mikeg_05 (Jan 1, 2009)

I would agree that you can use table 310.15(B)(6) since it is going from the main disconnect to the the panelboard. So if you used 2/3 you could bump it up to 125 amps, but 4/3 would work for 100.
Now if you have main panel in a garage and you put a sub panel down stairs lets say, could you use table 310.15(B)(6)?


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## Bob Badger (Apr 19, 2009)

mikeg_05 said:


> Now if you have main panel in a garage and you put a sub panel down stairs lets say, could you use table 310.15(B)(6)?


No you could not.


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## Magnettica (Jan 23, 2007)

mikeg_05 said:


> Now if you have main panel in a garage and you put a sub panel down stairs lets say, could you use table 310.15(B)(6)?



I would say no.... and I'm also not certain that 4/3 will be acceptable either because all of my bonding gets done at the main disconnect which will be outside so a 4-wire feeder is used to the panels. 


*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 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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## Bob Badger (Apr 19, 2009)

Magnettica said:


> I would say no.... and I'm also not certain that 4/3 will be acceptable either because all of my bonding gets done at the main disconnect which will be outside so a 4-wire feeder is used to the panels.
> 
> 
> *310.15(B)(6)*
> ...


It is not the 3 wire wording that is a problem, that only requires the service be a 3 wire service.

The problem is that a feeder to a sub panel is not a main power feeder as a main power feeder has to carry 100% of the dwelling unit load.


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## Magnettica (Jan 23, 2007)

Bob Badger said:


> It is not the 3 wire wording that is a problem, that only requires the service be a 3 wire service.
> 
> The problem is that a feeder to a sub panel is not a main power feeder as a main power feeder has to carry 100% of the dwelling unit load.


Ah, so if it was 1 MLO panel it would carry 100% of the load, but because I have 2 MLO panels the feeders do not carry 100% of the load.


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## mikeg_05 (Jan 1, 2009)

Magnettica said:


> I would say no.... and I'm also not certain that 4/3 will be acceptable either because all of my bonding gets done at the main disconnect which will be outside so a 4-wire feeder is used to the panels.
> 
> 
> *310.15(B)(6)*
> ...


I thought so. Well it says with or w/o the equipment grounding conductor. Id say its ok, maybe call the ahj see what they think


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## Dennis Alwon (May 9, 2009)

Magnettica said:


> Ah, so if it was 1 MLO panel it would carry 100% of the load, but because I have 2 MLO panels the feeders do not carry 100% of the load.


If I had an exterior 4 cir panel with one DP breaker feeding the a/c unit and the other DP breaker feeding the interior panel then I can no longer use T. 310.15(B)(6) to feed that interior panel. Odd huh-- take the load off the interior panel then I must use a larger wire for the same load (t.310.16). Strange, but it is how that section reads.


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## Mike Guile (Jan 14, 2010)

*weird*

That would be like running a 3" PVC main water line to house..then branch off with 4" PVC runs ??? sort of


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## Bob Badger (Apr 19, 2009)

Dennis Alwon said:


> If I had an exterior 4 cir panel with one DP breaker feeding the a/c unit and the other DP breaker feeding the interior panel then I can no longer use T. 310.15(B)(6) to feed that interior panel. Odd huh-- take the load off the interior panel then I must use a larger wire for the same load (t.310.16). Strange, but it is how that section reads.


I disagree, in my opinion the feeder never has to be larger than the service conductors due to 215.2(A)(3)


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## Dennis Alwon (May 9, 2009)

Bob Badger said:


> I disagree, in my opinion the feeder never has to be larger than the service conductors due to 215.2(A)(3)


 Yeah we've been thru this but NC state inspector (AHJ) disagrees with you. I tried to show him 215.2(A)(3) but he has a different take on that. :no:


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## Dennis Alwon (May 9, 2009)

215.2(A)(3) brings us back to 310.15(B)(6) which does not allow NM. SO.......


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## Bob Badger (Apr 19, 2009)

Dennis Alwon said:


> Yeah we've been thru this but NC state inspector (AHJ) disagrees with you.


I can't help it if they are listening to the electrical Guru and not the CMP.


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## Dennis Alwon (May 9, 2009)

Bob Badger said:


> I can't help it if they are listening to the electrical Guru and not the CMP.


IMO, the use of the term larger makes no sense and that article needs help. Technically, if we use #4 copper for the service entrance of a 100 amp service. Then, by the wording of 215.2 I could use #4 aluminum to the interior panel 100 amps since #2 aluminum would be larger than #4 and is not necessary. 

It makes no sense and contradicts 310.15(B)(6)


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## Bob Badger (Apr 19, 2009)

Dennis Alwon said:


> IMO, the use of the term larger makes no sense and that article needs help.


I agree.



> Technically, if we use #4 copper for the service entrance of a 100 amp service. Then, by the wording of 215.2 I could use #4 aluminum to the interior panel 100 amps since #2 aluminum would be larger than #4 and is not necessary.


I agree.



> contradicts 310.15(B)(6)


I see no contradiction.


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## Dennis Alwon (May 9, 2009)

Does 215.2 make exceptions for a sub panel that does not carry the entire load? No except that it does tell us to use paragraph 310.15(B)(6) which tells us it must carry the entire load and if it doesn't then we presumably must use T. 310.16 which would a conductor larger than the service conductor. See into the circle we go.


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## Bob Badger (Apr 19, 2009)

Dennis Alwon said:


> Does 215.2 make exceptions for a sub panel that does not carry the entire load? No except that it does tell us to use paragraph 310.15(B)(6) which tells us it must carry the entire load and if it doesn't then we presumably must use T. 310.16 which would a conductor larger than the service conductor. See into the circle we go.



I think you can make group of code sections a circle if do not choose to stop.


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## Magnettica (Jan 23, 2007)

You two have entered the gray area I mentioned previously.


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## bobelectric (Feb 24, 2007)

I keep tripping over my 40 ' leftover cut of 3#2 with # 6 grd,m.c. cable, I bought for $7.00/ft.copper.


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## JohnSham (Jan 7, 2010)

*measuring*

talking about measuring copper. I had to buy about 30 ft of 500MCM copper once to feed a panel ...and talking about taking a bunch of measurements. I think it was $10ft or something. I was off 6 ft. So I stripped and cashed in leftover.


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## kbsparky (Sep 20, 2007)

Magnettica said:


> Any idea how much per foot 2/3 romex is going for these days? Guy wants a price on a 2 family service with remote MLO panels in copper. I can't use 4/3 for 100 amp mains can I?


#4 should be fine here. Since there are 2 dwelling units involved, and each dwelling unit's total load would be supplied by a single feeder to that unit.

310.15(B)(6) does apply in this case, IMO.


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## Dennis Alwon (May 9, 2009)

kbsparky said:


> #4 should be fine here. Since there are 2 dwelling units involved, and each dwelling unit's total load would be supplied by a single feeder to that unit.
> 
> 310.15(B)(6) does apply in this case, IMO.


I believe that many of you guys are missing an important issue. 310.15(B)(6) is not valid for NM cable. If he wanted to use SE cable then that would be a different story.


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## Magnettica (Jan 23, 2007)

Dennis Alwon said:


> I believe that many of you guys are missing an important issue. 310.15(B)(6) is not valid for NM cable. If he wanted to use SE cable then that would be a different story.


Table 310.15(B)(6) 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


What kind of insulation is NM?


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## Dennis Alwon (May 9, 2009)

Magnettica said:


> Table 310.15(B)(6) 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,
> ...


We don't know what kind of insulation is in NM but we do know it is 90C. art.334.80. The point is that the Table specifies SE cable and those individual conductor insulations. It does not state NM cable thus you could not use it. Thhn and all those other conductor insulations are fine in conduit but not if it is inside a cable unless it is SE. Why I don't know. Even MC cannot be used


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## waco (Dec 10, 2007)

334.12(A)(3) states NM cannot be used as service cable. I have always taken that to include "feeders." I suppose it is arguable, although I have used NM as branch circuit/feeders where I have used a sub-panel as a disconnect.


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## Dennis Alwon (May 9, 2009)

waco said:


> 334.12(A)(3) states NM cannot be used as service cable. I have always taken that to include "feeders." I suppose it is arguable, although I have used NM as branch circuit/feeders where I have used a sub-panel as a disconnect.


Service cables are not feeders. Why would you take it to mean feeders. We have an entire section on services and service conductors and another section for feeders.

NM may be used for feeders but it cannot take advantage of T. 310.15(B)(6). It cannot be used for service entrance conductors. This is not really arguable unless you want to argue for argument sake. 

The service entrance conductors stop at the first disconnect.


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## waco (Dec 10, 2007)

Dennis Alwon said:


> Service cables are not feeders. Why would you take it to mean feeders. We have an entire section on services and service conductors and another section for feeders.
> 
> NM may be used for feeders but it cannot take advantage of T. 310.15(B)(6). It cannot be used for service entrance conductors. This is not really arguable unless you want to argue for argument sake.
> 
> The service entrance conductors stop at the first disconnect.


Seems to me, since NM cannot be used for service cable, then why should I use it for feeders when service cable works pretty well for both? I said I have used it (up to 6-3) to serve sub-panels used for disconnects, but notice, I also see that as a situation different from serving a MLO sub-panel serving multiple branch circuits.

I was only expressing a little bit of surprise that the code allows NM for "feeders," but not service cable, but I don't really much care, either. I'm happy with my style.


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## mlnk (May 17, 2011)

There is a section of the Code that says you do not have to use wire larger than the SE wire for any feeder, unless it is being de-rated. I am looking for the ref.


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