The Siemens 3RU2126-4CB00-8K is a premium thermal overload relay from the trusted SIRIUS 3RU2 Series, designed to provide reliable protection for three-phase motors against overload conditions, phase failure, and prolonged overcurrent operation. This relay features an adjustable current setting range of 17–22 A, Class 10 tripping characteristics, and is designed for direct mounting on Siemens Size S0 contactors, making it ideal for industrial motor control and protection applications.
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. Integrated phase-failure sensitivity provides additional protection against single-phasing conditions.
The Variant CB008K offers an adjustable overload release setting of 17–22 A, making it suitable for protecting motors used in pumps, compressors, fans, conveyor systems, HVAC equipment, packaging machinery, machine tools, and industrial automation installations. The relay is optimized for Siemens 3RT contactors and compact motor starter assemblies.
As part of the Siemens SIRIUS motor protection portfolio, the 3RU2126-4CB00-8K supports both manual and automatic reset modes and includes 1 Normally Open (NO) and 1 Normally Closed (NC) auxiliary contact for trip indication, signaling, and control circuit integration. Screw-type terminals ensure secure electrical connections and simplified installation.
Its compact S0 frame size, robust industrial construction, and reliable thermal tripping mechanism make it a preferred choice for motor control centers (MCCs), process industries, manufacturing plants, water treatment facilities, and material handling systems.
| Specification | Details |
|---|---|
| Product Name | Thermal Overload Relay |
| Part Number | 3RU2126-4CB00-8K |
| SKU | 3RU2126-4CB00-8K |
| Brand | Siemens |
| Product Family | SIRIUS 3RU2 |
| Product Type | Motor Protection Relay |
| Variant | CB008K |
| Current Setting Range | 17–22 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 |
| 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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