Switchboard W/Through Bus Rating

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new_ee

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I had made another post but I think it was too confusing. So let me start over.

I have three meter banks in an apt. building with the following loads (they have already had demand factors in table 220.32 applied):

meterbank 1 = 1069A
meterbank 2 = 1079A
meterbank 3 = 857A
total = 3004A

I want to use a horizontal bus switchboard setup with three main breakers serving the three meterbanks.

1) What would the bus need to be rated?

2) If i have the bus rated at 3000A and the 3 main breakers are rated 1200A, 1200A, and 1000A is that code compliant? My problem is that the breaker total is more than the 3000A bus rating so if the breakers all pulled close to their full ratings the bus would be loaded more than 3000A.

3)Can I take the meterbank load totals (before 220.32 demand factors are applied) and use 220.32 on the total combined load for the whole building(the demand factor would be less because a greater number of dwelling units would be included in the calculation)?
 
maybe i should break this question down even further:

can a switchboard bus be rated less than the main overcurrent devices that are feeding the loads?
 
A switchboard may have bussing that is rated less than the SUM of the breaker handle ratings (6 disconnect rule), however it cannot be rated less than the total expected load. Effectively treat the bus bar sizing the same as you would any other conductor.
 
The building total VA would be subjected to the demand factors for the service. And the feeders calculated for thier VA with demand for what is connected to them. You would not be summing the Amperage totals of the feeders to get the service size... See Annex D Example D4 -D6 That said you might want to re-calc from the begining. As it would make me wonder how you got the feeder Amps in the first place. Not to mention the numbers posted = 3005 ;)
 
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