I am of the opinion that that the bus bars are the service entrance conductors
If we're taking a poll I would tend to agree with this (assuming it's an UG Service) because of the definition of Service Entrance Conductors in Art. 100.
In other situations the GEC is sized according to the Service Entrance Conductors and not the load. It wouldn't seem consistant to start looking at the load now.
Say this house has all Gas appliances and therefore a low calculated load. It's 200A OH service requires a #4 GEC. I change it to a UG service and with no change in loads it wouldn't make sense to me that I can now use a much smaller GEC.
JMO
Bill
