4/0 AL SEU Question

[Buck Parrish]

In NC are y'all still useing seu 4/0 AL for a back to back meter - panel , 200 amp servoce on a SFD?

I haven't ever used it much and didn't know if it was still allowed after all the lobbyist got passed on the 08 book.

Also does any one know if or when the NEC 2011 has or when it will be adopted by the NC General Assembly?

Thannks in advance, for any input would be appreciated.

 

[Hv&Lv]

Yes, installed one last thursday using that cable.

 

[Buck Parrish]

thanks, your in NC ?

 

[Dennis Alwon]

For 200 amps it is fine to use 4/0 alum as a service conductor, assuming this is a residence. The problem is with ser used as a feeder.

 

[busman]

For 200 amps it is fine to use 4/0 alum as a service conductor, assuming this is a residence. The problem is with ser used as a feeder.

Just curious. What's the issue with 4/0 SER as a feeder?

Thanks

Mark

 

[Buck Parrish]

Just curious. What's the issue with 4/0 SER as a feeder?

Thanks

Mark

The Load it can carry has been reduced 310.15(b) 6. If it is not carrying the entire load of the residence.

So you can use 4/0 seu to feed your meterbase combo 200 amp feed through panel. If you put the AC on the meter base combo. You would have to go to 250 al ser to feed the inside 200 amp panel.

 

[infinity]

The Load it can carry has been reduced 310.15(b) 6. If it is not carrying the entire load of the residence.

So you can use 4/0 seu to feed your meterbase combo 200 amp feed through panel. If you put the AC on the meter base combo. You would have to go to 250 al ser to feed the inside 200 amp panel.

Why would the feeder conductors need to be larger than the service entrance conductors?

 

[Dennis Alwon]

Just curious. What's the issue with 4/0 SER as a feeder?

Thanks

Mark

Article 338.10(B)(4)(a) seems to make us use 60C in this situation-- 2008 NEC but 310.15(B)(6) allows us to use 4/0 if the entire load of the service is on the feeder. Many areas interpret 338.10(B)(4)(a) as overriding 310.15. In a 400 amp service with 2- 200 amp disconnects feeding 2- 200 amp sub panels then 4/0 would not be allowed.

 

[Dennis Alwon]

Why would the feeder conductors need to be larger than the service entrance conductors?

Our state inspector says so in spite of 215.2(A)(3)

 

[Buck Parrish]

Article 338.10(B)(4)(a) seems to make us use 60C in this situation-- 2008 NEC but 310.15(B)(6) allows us to use 4/0 if the entire load of the service is on the feeder. Many areas interpret 338.10(B)(4)(a) as overriding 310.15. In a 400 amp service with 2- 200 amp disconnects feeding 2- 200 amp sub panels then 4/0 would not be allowed.

Is that changing in 2011 ( is it going back to the normal way)?

Is NC going to adopt the NEC 2011 ?

 

[augie47]

I hesitate to take this step and I know Dennis is grinning as he knows we have fought this in TN and on the Forum numerous times.
AS Chief Inspector told me once that if you think the Code contradicts itself then you don't know the Code, therefore I don't know the Code
For those who have not been there, the problem arose when 338.10)(B)(4) deemed SE (SEU) ampacity was 60? for interior installations which essentially made 4/0 AL SE a 150 amp cable.
On the other side of the coin, 310.15(B)(6) allows 4/0 AL for a 200 amp service or MAIN feeder.
(In addition 215.2(B) can be thrown into the mix)
TN State inspectors have asked for a "ruling" on how to handle this perceived discrepancy for years with no answer. I'm not sure how it is handles elsewhere, but in TN you will find some inspectors who will allow a 4/0 AL to feed the service, but then require a 300 kcmil AL feeder, especially if a portion of the load is shed at an outside feed-thru panel.
Whether this is "Code" can and has been argued here numerous times. in the end it has become a AHJ call locally.
(all references are '08 Code)

 

[Dennis Alwon]

I don't know when or if the 2011 will be accepted. I assume it will be but the time keeps changing. There are some changes in 2011-- se is 75C if it is not in insulation and there is a chance by 2014 it will be changed to 75C regardless.

Gus How do you install a 300kcm in a lug that generally will only accept 250 kcm. This is why I pipe all my 200 amp panels-- then I can use 4/0 even for 400 amps as long as each panel isn't loaded more than 180 amps- calculated load.

 

[infinity]

TN State inspectors have asked for a "ruling" on how to handle this perceived discrepancy for years with no answer. I'm not sure how it is handles elsewhere, but in TN you will find some inspectors who will allow a 4/0 AL to feed the service, but then require a 300 kcmil AL feeder, especially if a portion of the load is shed at an outside feed-thru panel.

Am I the only one sitting here laughing at this? :lol:

 

[augie47]

Am I the only one sitting here laughing at this? :lol:

Definitely not, and I am not supporting that interpretation, but I think the CMPs have not done an adequate job of clarfying the discrepency.
In general, I find most inspectors in this area allow 4/0 AL at 200 amp for service and feeders based on 310.15(B)(6) and 215.2, but, apply 338.10 to branch circuits and smaller sub-panels (other than a "service" sub-panel)

 

[Dennis Alwon]

Am I the only one sitting here laughing at this? :lol:

Rob, if the ser went thru a space that was derated because of temp and other variables would you still think that a larger conductor was not needed. To me it makes sense except I don't agree with the 60C rule, esp since time has proven it is not an issue.

 

[infinity]

Rob, if the ser went thru a space that was derated because of temp and other variables would you still think that a larger conductor was not needed. To me it makes sense except I don't agree with the 60C rule, esp since time has proven it is not an issue.

My comment had nothing to do with derating or other factors. I was merely saying that to applying a basic rule of having #4/0 SEC's and then 300 kcmil feeder conductors after that is silly.

 

[Dennis Alwon]

My comment had nothing to do with derating or other factors. I was merely saying that to applying a basic rule of having #4/0 SEC's and then 300 kcmil feeder conductors after that is silly.

But it does have to do with derating. If the temp. of ser is rated 60C in the house then a larger conductor would be need to compensate for the de-rate cable.

 

[augie47]

great analogy, Dennis.
If your service conductors were outside and the associated feeder was routed thru an extremely high temperature area, we would be required to derate the feeder due to the ambient. Changing from a 75? or 90? conductor to a 60? one could also necessitate a change.

 

[Dennis Alwon]

great analogy, Dennis.
If your service conductors were outside and the associated feeder was routed thru an extremely high temperature area, we would be required to derate the feeder due to the ambient. Changing from a 75? or 90? conductor to a 60? one could also necessitate a change.

Thanks Gus, but I want to be clear that I don't think the code is clear about this. Another issue is why does SE cable as a feeder that may go thru a hole that has fire caulk get derated to 60C yet when the SE cable is back to back from a meter and may run thru one or 2 feet of insulation it is 75C.