What it is and what it does
The Siemens 3RU2136-4JB0-ZX95 is a SIRIUS thermal overload relay, S2 frame size, designed to protect motors against overload and phase failure. It's a Class 10 device, meaning it will trip within 10 seconds at 7.2× the current setting — that's the standard for standard-duty motor starting, not for high-inertia loads that need a Class 20 or 30. Rated for 690 V and sized for motor loads up to 30 kW at 400 V, 45 kW at 500 V, or 55 kW at 690 V. The auxiliary contacts handle 2 A at 24 V and 230 V, 3 A at 120 V, and 1 A at 400 V — enough for signalling back to a PLC input or a contactor coil. The note on this variant reads "for message 'Tripped'" — that means the auxiliary contact configuration is wired to give a positive signal when the relay has tripped, not just a status change. That's useful for a remote alarm or a PLC input that needs a definite state on trip.
Mounting and integration
Mounts directly onto a Siemens contactor — the fastening method is "contactor mounting", so it clips onto the front of the matching S2 contactor (like the 3RT1036 series). No separate DIN-rail footprint needed; it rides on the contactor, saving panel width. The mounting position is any orientation. Dimensions are 55 mm wide, 90 mm high, 105 mm deep — that's the depth from the contactor face to the back of the relay. The main circuit terminals are screw-type, accepting 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) solid or stranded wire. Use a PZ2 Pozidriv screwdriver with a 5–6 mm shaft diameter. Temperature-compensated from -40 to +60 °C, so it won't drift on a hot panel door or in a cold warehouse. Operating range is -40 to +70 °C; storage and transport range is -55 to +80 °C.