Ah, I think we have some misunderstanding here!
You seem to be talking about having a DP MCB as the main CU supply switch, where as I was thinking of the DSO/DNO supply fuse being replaced by a MCB which troubled me a bit.
This makes a bit more sense, as the DSO fuse would provide the ultimate back-up for a major fault and the MCB is then a combined switch and current limit that comes in below the fuse and saves the DSO trouble if someone overloads the CU total capacity.
We have always had DP incoming switches for the CU and as you say it is so sensible that you can isolate the lot to do a global IR test without having to remove cables and risk further faults being introduced.
You seem to be talking about having a DP MCB as the main CU supply switch, where as I was thinking of the DSO/DNO supply fuse being replaced by a MCB which troubled me a bit.
This makes a bit more sense, as the DSO fuse would provide the ultimate back-up for a major fault and the MCB is then a combined switch and current limit that comes in below the fuse and saves the DSO trouble if someone overloads the CU total capacity.
We have always had DP incoming switches for the CU and as you say it is so sensible that you can isolate the lot to do a global IR test without having to remove cables and risk further faults being introduced.