The Siemens 3RU2146-4KB00-8K is a reliable thermal overload relay from the SIRIUS 3RU2 Series, engineered to provide dependable motor protection against overload conditions, phase failure, and excessive current draw. Designed for industrial motor control applications, this relay features an adjustable current setting range of 57–75 A, Class 10 tripping characteristics, and compatibility with Size S3 contactors.
The relay operates using Siemens' proven thermal overload protection technology, continuously monitoring motor current and disconnecting the motor when overload conditions persist. This helps prevent overheating, insulation damage, reduced motor life, and costly downtime while improving operational reliability. Thermal overload relays in the SIRIUS 3RU2 range are specifically designed for current-sensitive motor protection and phase-loss detection.
The Variant KB008K is designed for contactor mounting and incorporates a thermal inverse-time delayed overload release with an adjustable setting range of 57–75 A. It is suitable for protecting medium and high-power motors used in pumps, compressors, conveyors, fans, HVAC systems, manufacturing equipment, and process automation installations.
As part of the Siemens SIRIUS motor protection portfolio, the 3RU2146-4KB00-8K supports both manual and automatic reset modes, allowing users to configure protection according to operational requirements and plant safety procedures. The relay also incorporates integrated 1 NO + 1 NC auxiliary contacts for trip indication and control circuit integration.
The device is designed with screw-type terminals for both the main and auxiliary circuits, ensuring secure electrical connections and simplified installation. Its compact S3 frame size allows seamless integration into motor starter assemblies, MCC panels, and industrial control systems.
Featuring a Class 10 trip characteristic, the relay provides rapid protection for standard motor starting applications while minimizing nuisance tripping during normal operation. In addition, the relay offers phase-failure sensitivity, helping protect motors from damaging single-phasing conditions.
Manufactured according to Siemens' stringent quality standards, the 3RU2146-4KB00-8K delivers dependable long-term performance in demanding industrial environments and is widely used across manufacturing facilities, water treatment plants, process industries, material handling systems, and infrastructure projects.
| Specification | Details |
|---|---|
| Product Name | Thermal Overload Relay |
| Part Number | 3RU2146-4KB00-8K |
| SKU | 3RU2146-4KB00-8K |
| Brand | Siemens |
| Product Family | SIRIUS 3RU2 |
| Product Type | Motor Protection Relay |
| Variant | KB008K |
| Current Setting Range | 57–75 A |
| Relay Size | S3 |
| Trip Class | Class 10 |
| Operating Principle | Thermal |
| Mounting Type | Contactor Mounting |
| Main Circuit Connection | Screw Terminal |
| Auxiliary Circuit Connection | Screw Terminal |
| Auxiliary Contacts | 1 NO + 1 NC |
| Reset Type | Manual / Automatic |
| Number of Main Poles | 3 |
| Protection Features | Overload & Phase Failure Protection |
| Application | Industrial Motor Protection |
| Manufacturer | Siemens |
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