Conductor size 310.15 b 6

[amary]

Understanding that I can size a single phase residential service to this table I am looking for a little help. I believe that this applies to one set of service entrance conductors, or feeders. My questions is as follows: I have a 400 amp meter main with 2 200 amp breakers feeding 2 30 circuit 200 amp panels. Should the conductors feeding these panels be sized using 310.15(b) (6) or should these conductors be size by 310.16?
In the 2005 NEC handbook terms like single set of conductors and the entire load are used. Therefore I am using 310-16

 

[charlie b]

Is either, or are both, of the 200 amp panels the main power source for a residence? For example, is one the main power panel in one half of a duplex, with the other being the main power panel for the other half?

Or are both in the same residence? And if so, what loads does each of them serve?

 

[augie47]

conductors

conductors

you, of course, can't go wrong using 310.16.
That said, the arrangement you deccribe is very commonplace in this area and sizing conductors by 310.15 (b) (6) is usually accepted.
If I'm not mistaken, the situation becomes more interestinh when you take into account conductor type (Cu vs AL).
As charlieb states: calculate your load.
But lets assume a load of less than 180 amps...then 4/0 AL is good in either case..allowed by table, or allowed by "next size overcurrent protection rule" 240.4. Now change it to 2/0 Cu.....acceptable by table but not by 240.4 since 165 is a standard OCO. Which would you rather have? a 2/0 Cu based on Table 210.15, or a 4/0 AL based on 240.4.....

 

[suemarkp]

This should be one of the easier parts of 310.15(B)(6). The conductors are service entrance conductors unless you have a 400A disconnect upstream of those two panels. There are no limititations (in print) as to number of sets of service entrance conductors, and the "main power feeder" clause should only apply to feeders, which these aren't. So the table should be allowed to apply.

That being said, I used 3/0 copper to each 200A panel on my 400A service...

 

[eprice]

From the original post:

... I have a 400 amp meter main with 2 200 amp breakers feeding 2 30 circuit 200 amp panels. Should the conductors feeding these panels be sized ...

Sounds to me like the conductors in question are between the (2) 200 amp breakers and the panels. They are feeders, not service entrance conductors.

 

[Bob NH]

NEC 310.15(B)(6) " . . . the main power feeder shall be the feeder(s) between the main disconnect and the lighting and appliance branch-circuit panelboard(s)."

The code recognizes multiple feeders and multiple panelboards.

I believe 310.15(B)(6) applies until you hit the "lighting and appliance branch-circuit panelboard(s)."

 

[suemarkp]

From the original post:

...

Sounds to me like the conductors in question are between the (2) 200 amp breakers and the panels. They are feeders, not service entrance conductors.

Sorry, you're right. I guess I can't read.