The Siemens 3RU2156-5CW10-8K is a high-performance thermal overload relay from the SIRIUS 3RU2 Series, engineered to provide reliable protection for three-phase motors against overload conditions, phase failure, and prolonged overcurrent operation. Designed for industrial motor control applications, this relay features a current setting range of 90–125 A, Class 10 tripping characteristics, and compatibility with Size S6 contactor systems.
The relay operates using Siemens' proven thermal overload protection technology, continuously monitoring motor current and disconnecting the motor when excessive heating conditions occur. This helps prevent motor winding damage, insulation deterioration, and costly downtime while improving overall system reliability.
The 3RU2156-5CW10-8K (Variant CW108K) is a CT-operated overload relay with a straight-through transformer design, making it suitable for higher-current motor applications. Siemens catalogs identify this model with a 90–125 A adjustable overload range and approximately 55 kW motor applications, depending on operating conditions.
As part of the trusted SIRIUS motor protection portfolio, the relay supports both manual and automatic reset modes, allowing users to configure protection behavior according to plant operating requirements and safety procedures. This flexibility makes it suitable for a wide variety of industrial installations.
The relay is designed for separate mounting applications and incorporates a busbar main circuit connection along with screw-terminal auxiliary connections, ensuring secure installation and dependable performance in demanding industrial environments.
Its Class 10 trip characteristic provides excellent protection for standard motor starting applications by balancing startup tolerance with rapid response to sustained overload conditions. This helps extend motor service life while reducing maintenance requirements.
Manufactured according to Siemens' stringent quality standards, the 3RU2156-5CW10-8K is widely used in motor starter assemblies, MCC panels, pumps, compressors, conveyors, HVAC systems, water treatment plants, manufacturing facilities, and industrial automation applications.
| Specification | Details |
|---|---|
| Product Name | Thermal Overload Relay |
| Part Number | 3RU2156-5CW10-8K |
| SKU | 3RU2156-5CW10-8K |
| Brand | Siemens |
| Product Family | SIRIUS 3RU2 |
| Product Type | Motor Protection Relay |
| Variant | CW108K |
| Current Setting Range | 90–125 A |
| Approx. Motor Rating | 55 kW |
| Relay Size | S6 |
| Trip Class | Class 10 |
| Operating Principle | Thermal |
| Design Type | CT Operated, Straight Through Transformer |
| Mounting Type | Separate Mounting |
| Main Circuit Connection | Busbar Connection |
| Auxiliary Circuit Connection | Screw Terminal |
| Reset Type | Manual / Automatic |
| Motor Protection Function | Overload Protection |
| Application | Industrial Motor Protection |
| Manufacturer | Siemens |
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