What it is and what it does
The Siemens 3RU2136-4KD0 is a SIRIUS thermal overload relay, size S2, designed for motor protection in the main current circuit. It uses a thermal bimetallic release to track motor heating and trips the contactor on overload, with a Class 10A trip characteristic — meaning it must trip within 10 seconds at 7.2× the current setting, a fit for standard motor start profiles on pumps, fans, and conveyors. Rated for 690 V, it carries power ratings of 37 kW at 400 V, 45 kW at 500 V, and 55 kW at 690 V — these are the AC-3e motor-switching values that govern real motor sizing. The note "for message 'Tripped'" on the listing signals this variant includes an auxiliary contact that changes state on trip, so a PLC or HMI can log the fault without a separate signal conditioner.
Integration and mounting
Mounts directly to the contactor via the M6 main contact fastening — no DIN rail bracket needed. The relay sits in any orientation, which simplifies panel layout when the contactor is already fixed. Screw-type terminals on the main circuit accept 2× (0.5 to 2.5 mm²) solid or stranded conductors; use a Pozidriv PZ 2 bit with a 5–6 mm shaft diameter for the terminal screws. Dimensions are 55 mm wide by 90 mm high by 105 mm deep — the S2 frame size fits alongside SIRIUS contactors in a standard 400 mm deep enclosure with room for gland plates and cable ducts. Temperature compensation is active from -40 to +60 °C, so the trip curve stays accurate even in a hot panel near a motor starter cluster.
Lifecycle and sourcing posture
Compliance documentation is in place: the substance prohibitance date of 10/15/2014 aligns with RoHS and REACH requirements for the EU market. The SIRIUS series carries UL, CSA, and CE approvals as standard for the product family, so the 3RU2136-4KD0 is accepted in panels destined for North America and Europe without additional certification work.