The Siemens 3RU2156-5BW10-8K is a robust thermal overload relay from the renowned SIRIUS 3RU2 Series, specifically engineered to provide dependable protection for three-phase motors against overload conditions, phase failure, and prolonged overcurrent operation. Designed for demanding industrial applications, this relay offers a current setting range of 70–100 A, Class 10 tripping characteristics, and compatibility with Size S6 motor starter systems. Siemens SIRIUS motor protection devices are widely used across industrial automation and power distribution applications for reliable motor safety and operational continuity.
The relay operates using the proven thermal overload principle, continuously monitoring motor current and disconnecting the motor when overload conditions persist. This helps prevent overheating, insulation damage, unexpected equipment failure, and costly production downtime while extending motor service life.
The Variant BW108K is a CT-operated thermal overload relay designed for medium-to-high current motor applications. Its adjustable current setting range of 70–100 A makes it suitable for protecting motors used in pumps, compressors, conveyor systems, HVAC installations, manufacturing equipment, and process automation machinery.
As part of the Siemens SIRIUS motor protection portfolio, the 3RU2156-5BW10-8K supports both manual and automatic reset modes, allowing users to configure the protection system according to plant operating procedures and safety requirements. This flexibility makes it suitable for a wide variety of industrial motor control applications.
The relay is designed for separate mounting and features a busbar main circuit connection along with screw-terminal auxiliary circuits, ensuring secure electrical connections and simplified integration into motor control centers (MCCs), switchboards, and industrial control panels.
Its Class 10 trip characteristic provides excellent protection for standard motor starting applications by balancing startup tolerance with rapid response to sustained overload conditions. In addition, the relay incorporates phase-failure sensitivity, helping protect motors from damaging single-phasing conditions.
Manufactured according to Siemens' stringent quality standards, the 3RU2156-5BW10-8K delivers reliable long-term performance in demanding industrial environments where motor protection is critical.
| Specification | Details |
|---|---|
| Product Name | Thermal Overload Relay |
| Part Number | 3RU2156-5BW10-8K |
| SKU | 3RU2156-5BW10-8K |
| Brand | Siemens |
| Product Family | SIRIUS 3RU2 |
| Product Type | Motor Protection Relay |
| Variant | BW108K |
| Current Setting Range | 70–100 A |
| Relay Size | S6 |
| Trip Class | Class 10 |
| Operating Principle | Thermal |
| Design Type | CT Operated |
| Mounting Type | Separate Mounting |
| Main Circuit Connection | Busbar Connection |
| Auxiliary Circuit Connection | Screw Terminal |
| Reset Type | Manual / Automatic |
| Protection Features | Overload & Phase Failure Protection |
| Application | Industrial Motor Protection |
| Manufacturer | Siemens |
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