Siemens Overload relay thermal for motor protection, 9 - 12.5A Part number 3RU2126-1KB0

Product Overview

The Siemens 3RU2126-1KB0 is a thermal overload relay from the SIRIUS 3RU2 series, designed to protect three-phase motors against overload, phase failure or phase asymmetry. It mounts onto compatible SIRIUS size-S0 contactors, providing adjustable current protection and an integrated auxiliary contact block for signalling or control feedback. With adjustable current range and robust trip response, it helps safeguard motors and ensure reliable operation in industrial environments.

Key Features

• Thermal overload relay — SIRIUS 3RU2 family, size S0
• Adjustable overload setting: 9 to 12.5 A
• Three-pole (3P) main circuit — protects 3-phase motors
• Integrated auxiliary contacts: 1 NO + 1 NC for signalling or control circuits
• Overload class: Class 10 — fast trip under overload conditions
• Phase-failure and phase-asymmetry protection included
• Manual or automatic reset options available
• Screw-terminal connections for main and auxiliary circuits — secure wiring
• Compact design — mounts directly on SIRIUS S0 contactors

Technical Specifications

• Article Number: 3RU2126-1KB0
• Product Type: Thermal Overload Relay (SIRIUS 3RU2)
• Size Class: S0 (for matching contactors)
• Current Setting Range: 9 … 12.5 A
• Poles (Main Circuit): 3 (three-phase protection)
• Auxiliary Contacts: 1 NO + 1 NC
• Rated Insulation Voltage: up to 690 V AC
• Surge Withstand / Impulse Voltage Rating: 6 kV
• Trip Class: Class 10 (thermal characteristic for overload protection)
• Motor Power Rating (AC-3): up to approx. 7.5 kW at 400–500 V, depending on motor and application
• Connection Type: Screw-type terminals for both main and auxiliary circuits
• Ambient Operating Temperature Range: –40 °C to +70 °C
• Protection Rating: IP20 (suitable for control-cabinet installation)
• Mounting: Direct mounting on compatible SIRIUS contactors

Applications

The 3RU2126-1KB0 is ideal for motor protection in industrial systems: controlling pumps, compressors, conveyor drives, fans, mixers and other three-phase motor-driven equipment. It provides reliable overload and phase-failure protection, while the auxiliary contact allows integration with control circuits, alarms or automation logic. Its compact size and direct-mount design make it suitable for compact motor starter panels and machine control cabinets.