4/0 AL feeder between service disc and remote panel?

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richwaskowitz

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Shelby Twp. MI, near Detroit
I have read through all the past posts I could find and am still not absolutely clear on this, and I need to be. Does table 310.15(B)(7) in 2011, apply to SER feeder conductors when installed between the service disconnect (an outdoor panel with only a 200 amp breaker) and the load center (the distribution panel for the entire home) ? My understanding is that as long as these feeders supply a panel which then supplies all of the loads in the dwelling, that 4/0 AL conductors would have a rating of 200 Amps. I have not received my 2014 Code yet so I do not know of the table number or the provisions have changed.
 
4/0 aluminum in an ser cable is good for 200 amp between the meter and the main disconnect and also between the main disconnect and the house panel as long as the house panel has the entire load of the dwelling fed from it. Take one load from the main disconnect that goes somewhere else than the feeder to the sub panel must follow 310.15(B)(16)
 
Dennis Alwon said:
4/0 aluminum in an ser cable is good for 200 amp between the meter and the main disconnect and also between the main disconnect and the house panel as long as the house panel has the entire load of the dwelling fed from it. Take one load from the main disconnect that goes somewhere else than the feeder to the sub panel must follow 310.15(B)(16)
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This confuses me also and I think its because I don't use much SE Cable.
For example if I have a 200 amp meter main on the outside of a house and the 2p 200 in the combo feeds the house panel and a breaker in the house panel feeds a detached garage I'm fine with using the SE to feed that panel, but , If the detached garage is fed by a 2p breaker in the outdoor panel, which would actually decrease the load on the house Panel, the Se cable is now not sufficient ? why ?


JAP>
 
jap said:
This confuses me also and I think its because I don't use much SE Cable.
For example if I have a 200 amp meter main on the outside of a house and the 2p 200 in the combo feeds the house panel and a breaker in the house panel feeds a detached garage I'm fine with using the SE to feed that panel, but , If the detached garage is fed by a 2p breaker in the outdoor panel, which would actually decrease the load on the house Panel, the Se cable is now not sufficient ? why ?


JAP>
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Correct --- Why? it has to do with diversity of the load. In some cases, like yours it makes no sense at all. In general a dwelling the load is based on the diversity of the loads so if you start taking away some of the loads then the diversity concept gets shot. Personally I cannot imagine this would ever be an issue but in some unusual cases.

Look at a 400 amp service with 2- 200 amp outdoor main panels. Suppose the electrician puts all the heating loads in one panel along with some other large loads and does all the smaller lighting and branch circuit loads in the other. The diversity concept gets a bit out of whack and one cannot guarantee the wire would be of sufficient size anymore
 
Dennis Alwon said:
Correct --- Why? it has to do with diversity of the load. In some cases, like yours it makes no sense at all. In general a dwelling the load is based on the diversity of the loads so if you start taking away some of the loads then the diversity concept gets shot. Personally I cannot imagine this would ever be an issue but in some unusual cases.

Look at a 400 amp service with 2- 200 amp outdoor main panels. Suppose the electrician puts all the heating loads in one panel along with some other large loads and does all the smaller lighting and branch circuit loads in the other. The diversity concept gets a bit out of whack and one cannot guarantee the wire would be of sufficient size anymore
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But although a possibility of a high imbalance, the rule for allowing the next higher standard breaker would still be in affect for a 200 amp breaker protecting a 176-200 amp rated wire would it not?


JAP>
 
I thought the reason was not so much that your taking load away from the main and creating diversity as much as it was that the full load on the house is diversified, meaning that not everything usually runs at one time, but, the individual branch circuits or feeders that may be running at the time may be running at full capacity and therefore those conductors could not be reduced.

JAP>
 
jap said:
But although a possibility of a high imbalance, the rule for allowing the next higher standard breaker would still be in affect for a 200 amp breaker protecting a 176-200 amp rated wire would it not?


JAP>
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Yes but in many cases seu or ser is rated 60C. If you pipe it then 4/0 aluminum is rated 180 amps and a 200 amp breaker is allowed but the load is limited to 180
 
Dennis Alwon said:
Yes but in many cases seu or ser is rated 60C. If you pipe it then 4/0 aluminum is rated 180 amps and a 200 amp breaker is allowed but the load is limited to 180
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That's where I differ from most since Pipe and wire is what I do.

Thanks,

JAP>
 
Dennis Alwon said:
4/0 aluminum in an ser cable is good for 200 amp between the meter and the main disconnect and also between the main disconnect and the house panel as long as the house panel has the entire load of the dwelling fed from it. Take one load from the main disconnect that goes somewhere else than the feeder to the sub panel must follow 310.15(B)(16)
Click to expand...

What about the feeder does not need to be larger than the service entrance conductors. So if the Service entrance is 200 a 4/0 AL and you have the main panel powering a garage with a say a 2 pole 30 and then a well at 2 pole 20 and then the main house sub panel at 200 amps with a 4/0 Al feeder.

In my opinion you are good to go as you are not required to have a wire size greater than the service entrance.
 
Sierrasparky said:
What about the feeder does not need to be larger than the service entrance conductors. So if the Service entrance is 200 a 4/0 AL and you have the main panel powering a garage with a say a 2 pole 30 and then a well at 2 pole 20 and then the main house sub panel at 200 amps with a 4/0 Al feeder.

In my opinion you are good to go as you are not required to have a wire size greater than the service entrance.
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The note actually says "The feeder conductors TO a dwelling unit".
Your scenario is describing a feeder to a subpanel IN the dwelling unit"

The way I read it for example is you could use #4 Thhn Copper for a 100 amp feed to a Panel in a dwelling unit from an outside disconnect , but, if you put a 2p 100 amp breaker in that panel to feed a subpanel #4 would not be large enough because by table 310.15(b)16 it is only good for 85 amps. you'd have to use #3 Thhn Copper.

At least I think that's what its saying.


JAP>
 
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