Mitsubishi FX External 24V

I have a customer with a MitsubishiFX32 Plc. At present the IO's are run off the on-board power supply. I am getting 22V DC out so would like to go to an external power supply. My question is, the documentation that I have seen shows a link between the S/S and 0V (on-board) terminal. Is this correct ? I am inclined to only connect to the S/S terminal from the external 0V.
Any help would be appreciated.

The S/S and 0V will be linked so that 24V+ is seen at the inputs
It is ok to put the 0V of your external 24V dc supply to either s/s or 0v