The Siemens 3RU2156-5CB10-8K is a high-performance thermal overload relay from the renowned SIRIUS 3RU2 Series, designed to provide dependable protection for industrial motors against overload, phase failure, and prolonged overcurrent conditions. Engineered for demanding motor control applications, this relay features a current adjustment range of 90–125 A, Class 10 tripping characteristics, and compatibility with Size S6 contactor systems.
The relay utilizes Siemens' proven thermal overload protection technology, continuously monitoring motor current and disconnecting the motor when overload conditions occur. This helps prevent overheating, winding damage, insulation degradation, and unexpected equipment failures, thereby extending motor life and improving operational reliability.
The Variant CB108K is a CT-operated thermal overload relay intended for separate mounting applications. Siemens catalog data identifies this model with a 90–125 A adjustable overload setting range and suitability for approximately 55 kW motor applications, depending on operating conditions and installation requirements.
As part of the Siemens SIRIUS motor protection portfolio, the 3RU2156-5CB10-8K supports both manual and automatic reset modes, allowing flexibility in configuring motor protection systems according to operational and safety requirements. This adaptability makes it suitable for a broad range of industrial automation and motor control installations.
The relay is designed for individual (separate) mounting and features a busbar main circuit connection along with screw-terminal auxiliary contacts, ensuring secure electrical connections and straightforward integration into motor starter assemblies, MCC panels, and industrial control systems.
Its Class 10 trip characteristic provides excellent protection for standard motor starting applications by balancing startup tolerance with rapid response to sustained overload conditions. Additionally, Siemens 3RU2 relays incorporate phase failure sensitivity, helping minimize motor damage during single-phasing conditions.
Manufactured to Siemens' stringent quality standards, the 3RU2156-5CB10-8K is widely used in pumps, compressors, conveyors, HVAC systems, water treatment facilities, manufacturing plants, process industries, and industrial automation systems where reliable motor protection is essential.
| Specification | Details |
|---|---|
| Product Name | Thermal Overload Relay |
| Part Number | 3RU2156-5CB10-8K |
| SKU | 3RU2156-5CB10-8K |
| Brand | Siemens |
| Product Family | SIRIUS 3RU2 |
| Product Type | Motor Protection Relay |
| Variant | CB108K |
| 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 |
| 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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