What it is and what it does
The Siemens 3RU2136-1KD0 is a SIRIUS thermal overload relay, Size S2, designed to protect motors against overload and phase failure. It mounts directly to a contactor, so the whole starter assembly stays compact on the DIN rail or mounting plate. Trip Class 10 means it will trip within 10 seconds at 7.2× the current setting — fast enough for standard induction motor starts but not so fast it nuisance-trips on normal inrush. The thermal bimetallic element tracks the motor's heating curve, so the relay follows the actual load rather than a fixed threshold. Rated insulation voltage is 690 V, with a 5.5 kW motor rating at 400 V AC-3e duty (the standard for squirrel-cage motors). The auxiliary switch is integrated — no separate add-on block needed for the trip indication or a remote reset circuit. The "for message 'Tripped'" note on the nameplate is a visual indicator that the relay has operated. When the bimetallic strip deflects, it pushes a mechanical flag — you see the word "Tripped" through a window on the front face. No need to meter the contacts; one glance tells you the starter needs a reset.
Mounting and wiring in the panel
Fastening method is contactor mounting — the relay clips directly onto the output side of a SIRIUS S2 contactor. This keeps the power wiring short and the assembly footprint tight. Mounting position is any orientation, which helps when the panel layout is tight. Main circuit terminals are screw-type, accepting 2 × (0.5 to 2.5 mm²) solid or stranded wire. The screwdriver spec is Pozidriv PZ2 with a 5–6 mm shaft diameter. Depth is 105 mm, width 55 mm, height 90 mm — fits a standard S2 starter slot. Temperature compensation is active from -40 °C to +60 °C, so the trip curve stays accurate even if the panel warms up near the motor. Operating ambient range is -40 to +70 °C; storage and transport go from -55 to +80 °C.
Lifecycle and sourcing reality
Substance prohibitance date is 10/15/2014, which aligns with the EU RoHS compliance timeline. The relay carries the usual Siemens documentation package — RoHS, REACH, and the IEC 60947-4-1 standard for electromechanical contactors and motor-starters.
How it compares to the 3RU2116-1FC1
The 3RU2116-1FC1 is the smaller S0-frame sibling in the same SIRIUS family. The 3RU2136-1KD0 (Size S2) handles higher motor currents — up to 5.5 kW at 400 V versus the S0 frame's lower power range. Both share Trip Class 10, the same contactor-mounting philosophy, and the integrated auxiliary switch. The physical footprint is larger on the S2, so it will not drop into a panel wired for an S0 starter without re-drilling the mounting holes and re-terminating the power cables.