Feeder size changes in NEC 2008?

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Old 03-28-08, 11:54 AM
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Feeder size changes in NEC 2008?

Hi guys:

Did the NEC 2008 change feeder sizes for "most" ampacities or only for 100A?

I don't have ready access to the 2008 code, so am asking the experts.

Per the NEC 2008, what is the correct feeder sizes for MLOs of 125A and 200A.

I know the old code said 4/0 AL was OK for 200A, but not sure about the new code.
 
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Old 03-28-08, 12:21 PM
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Originally Posted by billybard View Post
Did the NEC 2008 change feeder sizes for "most" ampacities or only for 100A?
The '08 code didn't change the ampacities; it narrowed the scope of the rule (310.15b6) that would allow one to use reduced size wires for panel feeders. In the '08 code reduced wire sizes may only be used for the primary feeder to a residential dwelling which carries the full load of the dwelling, not to subpanels which carry only a portion of the load. Those panels do not qualify for the 310.15b6 table ampacities and instead must use the 310.16 table ampacities.

I don't have ready access to the 2008 code, so am asking the experts.
If you have a previous version, tables 310.15b6 and 310.16 are the same; the only difference is the wording as to when 310.15b6 may be used.

Per the NEC 2008, what is the correct feeder sizes for MLOs of 125A and 200A.
The feeders must be four wire (hot, hot, neutral, ground) and

AL: 125A = #1/0, 200A = 250 kcmil
CU: 125A = #1, 200A = #3/0

Now if these subpanel(s) carry the full load of the dwelling, they still qualify for 310.15b6 which is:

AL: 125A = #1/0, 200A = #4/0
CU: 125A = #2, 200A = #2/0
 
 

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