got the service inspection for this job. The neutral does not need to be in panel. Ground does. not sure why you would suggest a non center tap delta would need a neutral.
Inspector said 2/0 is perfect but cited main breaker as a switch and not an over current protection device. He did mention I realy didnt need a main because it would be under the 6 or less disconnect rule and could get away with a main lug panel. I still think the 150 amp main is ok because it is not protecting the service conductors from a short between power company and lugs on breaker. It only protects if buss fails or someone adds too much amperage on the branch circuits. either way of thinking..the 2/0 is good.
The "grounded" service conductor must be brought to service disconnecting means if the system is grounded, 3 phase 3 wire can be corner grounded. If it is an ungrounded system you must have ground fault detection/indication equipment.
Is your main a switch or a circuit breaker? Like you said you may not need a single main because of the six disconnect rule, but a switch does not provide any overcurrent protection, a circuit breaker does. The service main overcurrent device does not protect service conductors from short circuits or ground faults ahead of the device, it does protect them from overload conditions though.
And back to one of your main questions - you are correct that 2/0 (aluminum) ampacity is 135 and next standard size higher can be used which is 150 as long as the connected load doesn't exceed the conductor ampacity of 135. If using copper conductor you could use 1 AWG which is good for 130 amps and still use the next size up 150 amp overcurrent device so long as your load is not more than 130 amps.
