The Siemens 3RU2126-1KJ0 is a SIRIUS thermal overload relay, size S0, with a CLASS 10 trip characteristic. It's designed for motor protection in control panels, directly mounting onto a contactor. The CLASS 10 rating means it trips within 10 seconds at 7.2× the set current, matching the thermal curve of standard induction motors during a stall — no nuisance tripping on a normal start, but fast enough to protect the winding before insulation damage sets in.
Ratings and fit
Rated for main circuits up to 690 V and operating at 50/60 Hz. The auxiliary switch is integrated and carries the following contact ratings: 2 A at 24 V, 3 A at 120 V, 2 A at 230 V, 1 A at 400 V, and 0.3 A at 60 V. These figures govern the control-circuit load it can switch — a PLC output or relay coil drawing, say, 0.5 A at 24 V is well within margin; a 2 A solenoid at 120 V is at the limit. The S0 frame size and 45 mm width mean it occupies a single 45 mm slot on the DIN rail when mounted on its matching contactor, leaving room alongside for the motor circuit breaker.
Compliance and environment
Operating temperature range is -40 to +70 °C; storage and transport range is -55 to +80 °C. Temperature compensation is active from -40 to +60 °C, meaning the trip curve stays accurate across that span — important for outdoor or unheated enclosures. The MTTF at high demand rate is listed at 2,280 years, reflecting the relay's passive, fail-safe design. Substance prohibitance date is 10/01/2009, consistent with RoHS compliance. Ring cable lug connection is specified for the main current circuit.