I've heard about buildings in heavily loaded downtown areas served with what's called a "network service." To me, I look at this setup as as a system of large vault type transformers installed in the street that are paralleled onto the secondary mains and connected with a special switch called a "network protector." I've seen a special kind of electric meter called a "self contained network meter" and needs a fifth terminal? What is the difference between a 120/208 Y network service and a standard 120/208 Y service? I don't understand why a service like this needs a special meter. Perhaps I've got it confused.
If anyone can explain this to me I'd be most greatful. Thanks.
You may be encountering different uses of the term 'network service', with entirely different meanings.
I have seen the term used to describe 120/208 'single phase' service, such as might be used for individual residences in an apartment building. Such a service is really two legs of a 208/120 wye, and so at the basic physics level is not really 'single phase'; but is used in the same fashion as a residential single phase service.
As to why two legs of a 120/208 service requires a different meter from a 120/240 service: A standard meter for 120/240 single phase service 'cheats' and is not 'blondel compliant'. The 'blondel theorem' basically says that to correctly meter a three wire service you need to make _two_ voltage measurements (say the two leg-neutral voltages), and _two_ current measurements (say the two 'hot' leg currents). A standard 120/240 meter simply makes one voltage measurement (the leg-leg voltage) and then assumes that the leg-neutral voltage is exactly 1/2 of this value. In other words the meter ignores any phase difference or imbalance.
Because of the phase difference present in a two leg 120/208 service, such a meter would read anywhere up to 14% low, not accurate enough for utility metering.
Basically what you are saying is that you need a meter with two voltage coils, and have each coil connected between the neutral and each hot leg. I would imagine that the neutral would get connected to the sideways fifth terminal, instead of with a standard 120/240 v where the meter is not connected to the nuetral at all (one voltage coil that gets 240, connected to L1 & L2)