The Siemens 3RV1935-1BA00-0FJ0 is a 3-phase busbar designed to feed two S2-frame circuit-breakers from a common line supply, with a 55 mm division between the breaker mounting positions. It's the factory-assembled link that saves running individual phase jumpers across the breaker terminals — one piece, one torque spec, fewer points to check during commissioning.
This busbar clips into the S2 breaker footprint on a DIN rail assembly. The 55 mm division matches the standard spacing between two S2 frame breakers mounted side-by-side. No additional wiring between phases is needed — the busbar carries L1, L2, and L3 across both breaker positions internally.