Dual meter Grounding?

[Adamjamma]

Yes, you can find this in 230.90(A) exception 3.

Note that for 4/0 aluminum and when feeding other than just one individual dwelling the ampacity of the conductor is only 180 amps and not 200.

Exception No. 3: Two to six circuit breakers or sets of fuses shall be permitted as the overcurrent device to provide the overload protection. The sum of the ratings of the circuit breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the calculated load does not exceed the ampacity of the service conductors.

So in this instance you are calling for a main panel then of only the four panel feeds to get the two to six circuits? Thus feeding each panel from its own breaker? This then would also mean the main breaker at this panel then simultaneously disconnects all four panels under it... Very interesting.
If it was done, due to the limits on number of breakers, you could not then do this in a series system, or would you if using through block panels? I mean, I know that you could do it using riser panels, the main cable being the feeder, and the panels thus getting the full voltage needed at each panel...
Still trying to get a handle on these bigger systems.

 

[kwired]

Exception No. 3: Two to six circuit breakers or sets of fuses shall be permitted as the overcurrent device to provide the overload protection. The sum of the ratings of the circuit breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the calculated load does not exceed the ampacity of the service conductors.

So in this instance you are calling for a main panel then of only the four panel feeds to get the two to six circuits? Thus feeding each panel from its own breaker? This then would also mean the main breaker at this panel then simultaneously disconnects all four panels under it... Very interesting.
If it was done, due to the limits on number of breakers, you could not then do this in a series system, or would you if using through block panels? I mean, I know that you could do it using riser panels, the main cable being the feeder, and the panels thus getting the full voltage needed at each panel...
Still trying to get a handle on these bigger systems.

"Bigger system" isn't a requirement to be able to use the six disconnect rule. One could have a limited load application that is two to six 30 amp fused switches as the service disconnecting means, and 15 amp fuses in each disconnect, with a common service conductor sized to the connected load. Example might be a pumping station of some sort. Such thing is usually more common to see a panelboard for 120/ 208 or 240, but maybe if it were 480 volts you might see 2-6 disconnects for limited load applications as smaller circuits as they may cost less than a 480 volt panelboard would in such applications. This is what we usually see for irrigation installations around here, a 30 amp 480 volt fuse disconnect as service disconnect for the irrigation machine and then a pump panel (rated for service equipment) as the service disconnect for the well, so typically two service disconnecting means but one service drop or lateral supplying them.

The exception 3 mentioned above is for section covering overcurrent protection of the service conductor. Basically you must provide overcurrent protection based on conductor ampacity, but the exception is saying when there is more than one (permissibe) service disconnecting means a common supply conductor only needs to be sufficient size to carry the connected load, even if the sum of the overcurrent devices is more than conductor ampacity. This does come in handy with larger capacity applications as well though as you can have say a total load calculation of 900 amps, split it over three 400 amp service disconnecting means but supply them with only 900 amps of conductor. Those three 400 amp mains can be supplied with 500 copper if each is not loaded to more than 380 amps.

If one went with a single 1200 amp main instead on the same load you would need three parallel runs of 600 copper for the 1200 amp main, and may still come off that with 3-400 amp switches or breakers anyway, so more overall cost to supply the same thing. Adding more load down the road - you already have three service disconnects and are allowed up to six - so one must consider pro's and con's and have some knowledge of what might be coming in future for best overall design.