What it is, in panel-builder terms
The ABB 1SVR427071R0000 is the CP-A RU redundancy unit — a DIN-rail module that sits between two parallel DC power supplies and the downstream load, diode-OR'ing them into a single output so either supply can carry the panel on its own if the other drops. It accepts two inputs rated up to 20 A each and delivers one output rated up to 40 A, which is the sizing rule the redundancy unit imposes on the upstream supplies: each feed has to be capable of carrying the full panel load by itself.
How the ratings drive the build
The 2 × 20 A input / 1 × 40 A output class is what fixes the rest of the BOM around it — pick two supplies that each meet the panel's full load current, not supplies that split the load, because the redundancy contract only holds when either unit alone can sustain the bus.
Handling and mounting note
At 0.86 kg the unit has real mass on the DIN rail — it wants solid end-stop clamping on both sides, not just the spring of the rail alone, especially in cabinets that see vibration.