In what combination I should use Modicon Quantum Power supply 140CPS12420 for redundant operation with loading capacity of 16A
If you install three power supply 140CPS12420 in a rack then load (16 amp) will be share on the three powersupplies. (5.3 amp each). If one of the power supply fails then the load will be share with the two power supply available (8 amp each). But at this moment, the redundancy will not be available because if a second power supply fail, the single power supply remains would not be able to deliver 16 amp.
You should also refer to the below faq link for more information on redundant power supply.