"Sub Panel" feeder

[electricmanscott]

This is one that came up in a code review class and I think the wrong info was given out. I won't say who gave it out as he will probably read this and there is no reason to throw him under the bus. We talked about it during break time and I think he, another guy, and myself agreed what the real answer should be.

Based on the 2008 NEC what size conductors would be required to feed a 100amp "sub" panel in a dwelling. Fed from a 200 amp servcie, and figure se cable aluminum and or copper.

 

[peter d]

I don't know the whole '08 rule but I'm guessing it would have to be 1/0 AL.

 

[JohnJ0906]

1/0 AL SEU = 100 amps @ 60 deg C

edit to add - #2 CU is 95 amps @ 60 deg C, so if your computed load is under that you are OK, otherwise #1 CU

 

[JohnJ0906]

To be specific, Table 310.15(B)(6) does not apply, and SE cable is restricted to the 60 deg. column. ('08 NEC)

 

[don_resqcapt19]

The issue here is the change in 338.10(A)(4)(a). In the 2005 code you were required to comply with Parts I and II of Article 334 except 334.80 when using SE cable for a feeder or branch circuit. Under the 2008 code you must also comply with 334.80 which limits you to the 60?C ampacity.
Don

 

[celtic]

Based on the 2008 NEC what size conductors would be required to feed a 100amp "sub" panel in a dwelling. Fed from a 200 amp servcie, and figure se cable aluminum and or copper.

Final answer ~ 1/0 AL or #1 CU

You may have missed this post (#10 ) in your previous thread:
Code class this weekend..

 

[bob]

The issue here is the change in 338.10(A)(4)(a). In the 2005 code you were required to comply with Parts I and II of Article 334 except 334.80 when using SE cable for a feeder or branch circuit. Under the 2008 code you must also comply with 334.80 which limits you to the 60?C ampacity.
Don

Don
Do you know why the panel made this change.

 

[JohnJ0906]

Don
Do you know why the panel made this change.

Check out this thread. I think Iwire posted the ROP

http://forums.mikeholt.com/showthread.php?t=94744

 

[electricmanscott]

You guys are sharp and on the ball. I am sure there will still be many installations where #2 al ser will be run and fused at 100 amps per 310.15(B)(6) Which was never allowed in this type of installation (sub panel) imo.

 

[electricmanscott]

John, I didn't mean to steal your thunder, guess I missed your thread.

I am not even clear on this myself. The more I read it the less I unmdrestand it.

Does 310.15B6 Overrule everything?

The way that it is written the requiremnts for interior installation of branch circuits and feeders are to be installed in accordance with the NM rules and that would require se to be used based on the 60c column. So if I have a 200amp service with four meters (typical 3 family) where I feed 100 amp discos on the outside of a dwelling. From the discos I run ser into the apts does that table apply? If it does what allows it?

I am about to install a service in this exact scenario. Sure would like to do it only once. :smile:

 

[ptonsparky]

John, I didn't mean to steal your thunder, guess I missed your thread.

I am not even clear on this myself. The more I read it the less I unmdrestand it.

Does 310.15B6 Overrule everything?

The way that it is written the requiremnts for interior installation of branch circuits and feeders are to be installed in accordance with the NM rules and that would require se to be used based on the 60c column. So if I have a 200amp service with four meters (typical 3 family) where I feed 100 amp discos on the outside of a dwelling. From the discos I run ser into the apts does that table apply? If it does what allows it?

I am about to install a service in this exact scenario. Sure would like to do it only once. :smile:

310.16(6) allows this via the definition of main power feeder: "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 of by feeders, or both, all loads that are part or associated with the dwelling unit."

Feeding another panelboard from the first would require a larger SE cable to the second.

 

[iwire]

Feeding another panelboard from the first would require a larger SE cable to the second.

Tom a feeder never has to be larger then the service conductors supplying them.

2005 NEC 215.2(A)(3)

 

[ptonsparky]

Says the same thing in '08 310.16(6) in the next breath.

 

[ptonsparky]

OK, from 100A to 100A panel,SE cable is same size via table 310.15(B(6) but if I go from a 200 amp panel then to a 100, I can't use the table.

 

[iwire]

OK, from 100A to 100A panel,SE cable is same size via table 310.15(B(6) but if I go from a 200 amp panel then to a 100, I can't use the table.

That is how I see it. :smile:

 

[ptonsparky]

Well, golly gee if we both agree, it must be right.:grin: Might as well close this thread.

 

[electricmanscott]

Well, golly gee if we both agree, it must be right.:grin: Might as well close this thread.

Don't close it yet. My questions have not been answered.

Does table 310.15B6 Overrule the other applicable articles? They seem to contradict each other. I am confused. :-?

 

[iwire]

Don't close it yet. My questions have not been answered.

How about this?

I won't close it if you can find a different signature, :smile:

Does table 310.15B6 Overrule the other applicable articles? They seem to contradict each other. I am confused. :-?

My first impression is yes, but can you be more specific?

Which other Articles?

 

[petersonra]

IMO the feeder can be #14.

 

[electricmanscott]

My first impression is yes, but can you be more specific?

Which other Articles?

The articles we were talking about, 338.10(B)4 (a) where it gives the requirement for Installation methods of se, specifically branch circuits and feeders. This is the part that specifies the methods for "interior installations".

My example was a 200 amp service to 4 gang meter socket. Four 100 amp discos nippled from the meters on the outside of the house. From there ser is run to panels inside the apartments.

I am trying to understand which applies here and why. 310.15B6 Would allow #2 al. But 338.10(B)4 says se cable used as feeders and branch circuits (I am assuming we call these feeders, is this where I run astray?) as interior wiring, this would be interior, shall be installed to comply with part 2 of article 334. 334.80 says to use the 60 degree colum for determing ampacity for nm cable which would also apply to se cable. What's the deal?