Adjustable trip class — CLASS 5E, 10E, 20E, 30E
The 3RB3123-4RE0: Trip class is field-selectable among 5E, 10E, 20E, and 30E. This lets you match the relay's thermal curve to the motor start profile: a 5E setting trips fast (good for short-duration starts like centrifugal pumps), while 30E allows longer inrush (needed for high-inertia loads like conveyors or crushers). The relay trips when motor current exceeds the upper current setting value x 3.5 (maximum) and resets when current drops below the lower current setting value (minimum). This hysteresis prevents nuisance re-closure on a still-running motor.
The S0 footprint (width 45 mm, height 109 mm, depth 85 mm) is the standard Siemens frame size for contactors up to about 40 A. It occupies one 45 mm-wide slot on the DIN rail when mounted to its matching contactor. Main circuit terminals accept solid wire 2x (0.25 … 1.5 mm²) or stranded up to 1x 10 mm². The screwdriver specification is Pozidriv PZ2 with a shaft diameter of 5 to 6 mm.
Auxiliary contact ratings and environmental limits
The signalling contact (for message 'tripped') is rated 2 A at 24 V, 4 A at 120 V, and 3 A at 230 V — these cover typical PLC input and relay coil loads across common control voltages. Operating temperature range is -25 … +60 °C with full temperature compensation over that span. Storage and transport range is -40 … +80 °C. Vibration resistance is 1–6 Hz at 15 mm amplitude, 6–500 Hz at 20 m/s² for 10 cycles; shock resistance is 15 g / 11 ms.