What the CLASS 10 trip means for your motor
The 3RU2126-4AB0: That's the right speed for standard induction motor starts where the inrush doesn't linger; if you're starting high-inertia loads that need a longer acceleration ramp, you'd want a CLASS 20 or 30 relay instead.
Mounting and wiring — what fits where
This is a size S0 relay that mounts directly onto the contactor — no DIN rail bracket needed. The fastening method is contactor mounting, so it clicks onto the matching SIRIUS contactor and shares the same busbar connection. Screwdriver tip is Pozidriv PZ2, shaft diameter 5 to 6 mm.
If you're replacing a 3RV6021-4DA10 in an existing panel, check the contactor interface — the 3RU2126-4AB0 is a size S0 relay that mounts on SIRIUS contactors, while the 3RV6021 series uses a different mounting interface. Physical swap without rewiring depends on the contactor model already in the panel.