What it is and what it does
The Siemens 3RU1126-1KD1 is a SIRIUS thermal overload relay, size S0, designed to protect three-phase motors against overload and phase failure. It mounts directly to a contactor or standalone, and its Trip Class 10 response means it will trip within 10 seconds at 7.2× the set current — standard for general-purpose motor starting where the load doesn't hang on a long acceleration ramp. The main current circuit uses screw-type terminals, while the auxiliary and control circuit uses cage clamp terminals — a split that saves time on the panel: power wires get a secure screw termination, and signal wiring gets a tool-free push. Rated for 100 % relative humidity during operation and IP20 on the front, so it lives inside a panel with no special gasketing.
Sourcing and lifecycle
Compliance documentation includes ATEX approval (DMT 98 ATEX G 001) for explosive atmospheres, and substance prohibitance per RoHS as of July 1, 2006. The reference code per IEC 81346-2 is F, which maps to a protective device in your documentation tree.
Mounting and integration
Mounts standalone or directly onto a SIRIUS contactor. The mounting position is flexible: vertical surface with ±135° rotation and ±45° tilt front-to-back. Clearance: 0 mm upwards, forwards, and backwards; 6 mm at the side; 0 mm downwards — so you can pack it tight against the panel wall or adjacent devices, just leave 6 mm on the side for airflow. Dimensions are 97 mm high, 45 mm wide, 96 mm deep — a compact S0 footprint that fits standard DIN-rail enclosures. Shock resistance is 8g for 10 ms, so it holds up in mobile or high-vibration environments like conveyor drives or pump skids.
Key ratings and what they mean
Trip Class 10 is the headline: it means the relay will trip within 10 seconds at 7.2× the current setting. That's the right choice for standard induction motors that don't need a long start time — a fan or pump that comes up to speed in a few seconds. If your load has a high inertia (like a centrifuge), you'd want a Class 20 or 30, but for most general-purpose motor circuits, Class 10 is the default. Surge voltage resistance is rated at 6 kV, which covers the typical transient environment in an industrial panel without needing additional surge suppression. The operating temperature range is -20 to +70 °C, with storage and transport from -55 to +80 °C — fine for unheated warehouses or truck decks in winter.