What This Part Is
The Siemens 3RU2126-1KC0 is a SIRIUS thermal overload relay in the S0 frame size, rated for main circuits up to 690 V. It's the overcurrent protection element you mount directly onto a contactor — the part that watches motor current and trips when the load stays high too long. The integrated auxiliary switch signals the tripped state back to the PLC or annunciator.
Trip Class and What It Decides
CLASS 10 means this relay trips within 10 seconds at 7.2× the set current. That's the standard for standard-duty motor starting — pumps, fans, compressors that accelerate unloaded. If you're protecting a high-inertia load (centrifuge, flywheel) that needs a longer acceleration ramp, CLASS 10 is too fast; you'd want CLASS 20 or 30. For most general-purpose three-phase motors on 50/60 Hz supply, CLASS 10 is the correct call.
Mounting and Integration
S0 frame size, 45 mm wide, 102 mm tall, 84 mm deep. Fastens directly to the contactor — no DIN rail required, no extra bracketry. Spring-loaded terminals on the main circuit accept 2x (0.5... 2.5 mm²) solid or stranded. Mounting position is any orientation, which helps when the panel layout is tight. The screwdriver tip needed is 3.0 x 0.5 mm, shaft diameter 3 mm — keep that driver in the panel kit.
Environmental Reach
Operates from -40 °C to +70 °C, with temperature compensation active across -40 °C to +60 °C — so the trip curve stays accurate even in a hot enclosure or a cold nacelle. Storage and transport range is -55 °C to +80 °C. That's a part that survives the ride in an unheated truck and still works when you power it up at site.
Sourcing and Lifecycle
Current production. Sourced and quoted to order against an RFQ through independent distribution; availability and current pricing confirmed at quote time.