What it is and what it does
The Siemens 3RU2136-4FB0-ZX95 is a SIRIUS thermal overload relay, Size S2, designed to protect motors against overload and phase failure. It mounts directly to a contactor via the contactor mounting fastening method, making it a compact, integrated motor starter component for a control panel. The thermal overload release design means it uses a bimetallic strip that heats up and trips based on motor current, providing inverse-time protection. The CLASS 10 trip class means it will trip within 10 seconds at 7.2x the set current, suitable for standard induction motor starting — enough time for the motor to accelerate under load without nuisance tripping on start-up, but fast enough to protect against a locked rotor. The auxiliary switch is integrated into the relay body, with contacts rated for pilot duty across common control voltages: 2 A at 24 V, 3 A at 120 V, 2 A at 230 V, 1 A at 400 V, and 0.75 A at 690 V. The note "for message 'Tripped'" indicates this auxiliary contact signals the tripped state back to the PLC or annunciator.
Ratings and fit for motor protection
This relay is rated for motors up to 18.5 kW at 400 V, 22 kW at 500 V, and 37 kW at 690 V. For North American applications, it carries current ratings of 40 A at both 480 V and 600 V. The maximum AC-3e rated voltage is 690 V, covering most low-voltage industrial motor circuits. Power dissipation per pole is 5.2 W, which matters for thermal management inside a sealed enclosure — three poles at full load add 15.6 W of heat that must be considered in the panel cooling calculation. The relay operates from -40 to +70 °C during operation, with temperature compensation active from -40 to +60 °C, ensuring accurate tripping regardless of ambient temperature shifts in an outdoor or unconditioned enclosure. Storage and transport range extends from -55 to +80 °C.
Mounting and wiring
Physical dimensions are 55 mm wide, 90 mm high, and 105 mm deep — the S2 form factor fits standard Siemens contactor footprints. Mounting position is any orientation, giving flexibility in dense panel layouts. Main contacts use screw-type terminals accepting 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) solid or stranded wire. The screw size for main contacts is M6. Use a Pozidriv PZ 2 screwdriver tip with shaft diameter 5 to 6 mm for termination.
Lifecycle and compliance
Substance prohibitance date is October 15, 2014, aligning with RoHS compliance requirements for the European market. This confirms the part meets the restricted substance limits effective from that date.