The Siemens 3RU2126-4FB00-8K is a high-performance thermal overload relay from the trusted SIRIUS 3RU2 Series, engineered to provide reliable protection for three-phase motors against overload conditions, phase failure, and excessive current draw. Designed for industrial motor control applications, this relay features an adjustable current setting range of 18–25 A, Class 10 tripping characteristics, and compatibility with Size S0 Siemens contactors, making it ideal for compact motor starter assemblies and automation systems. The SIRIUS 3RU2 range is specifically developed for dependable motor protection with direct contactor mounting.
The relay operates using Siemens' proven thermal overload protection principle, continuously monitoring motor current and disconnecting the motor when overload conditions persist. Its inverse-time delayed tripping characteristic helps prevent motor overheating, insulation damage, and premature motor failure while allowing normal motor starting currents. The relay also provides phase-failure sensitivity for enhanced motor protection and operational reliability.
The Variant FB008K offers an adjustable overload release setting of 18–25 A, making it suitable for protecting motors used in pumps, compressors, conveyor systems, fans, HVAC equipment, machine tools, packaging machinery, and industrial automation installations. Its compact S0 frame size allows efficient integration into motor control panels, switchboards, and motor starter combinations.
As part of the Siemens SIRIUS motor protection portfolio, the 3RU2126-4FB00-8K supports both manual and automatic reset modes, providing flexibility for different operating requirements and maintenance procedures. The relay is designed with screw-type terminals for secure wiring and dependable electrical connections in demanding industrial environments.
Manufactured according to Siemens' stringent quality standards, the 3RU2126-4FB00-8K delivers dependable long-term performance in manufacturing facilities, water treatment plants, process industries, material handling systems, and infrastructure projects.
| Specification | Details |
|---|---|
| Product Name | Thermal Overload Relay |
| Part Number | 3RU2126-4FB00-8K |
| SKU | 3RU2126-4FB00-8K |
| Brand | Siemens |
| Product Family | SIRIUS 3RU2 |
| Product Type | Motor Protection Relay |
| Variant | FB008K |
| Current Setting Range | 18–25 A |
| Relay Size | S0 |
| Trip Class | Class 10 |
| Operating Principle | Thermal |
| Mounting Type | Direct Contactor Mounting |
| Main Circuit Connection | Screw Terminal |
| Auxiliary Circuit Connection | Screw Terminal |
| Reset Type | Manual / Automatic |
| Number of Poles | 3 |
| Protection Features | Overload & Phase Failure Protection |
| Application | Industrial Motor Protection |
| Manufacturer | Siemens |
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