Overview
The Siemens 3RB3123-4NB0 Electronic Overload Relay is a high-performance motor protection device designed to safeguard electric motors from overloads, phase failures, and internal ground faults. Engineered with Siemens’ advanced electronic protection technology, this relay ensures reliable motor operation while minimizing downtime and maintenance costs.
This overload relay supports a current range of 0.32 to 1.25 A, making it ideal for low-current motor applications. It is built in Size S0 and optimized for contactor mounting, allowing seamless integration into motor control systems. The relay features adjustable tripping classes from Class 5 to Class 30, offering flexibility to suit different motor startup conditions and load requirements.
With manual and automatic reset options, screw-type terminals for both main and auxiliary circuits, and internal ground fault detection, the Siemens 3RB3123-4NB0 provides comprehensive protection, accuracy, and long-term reliability in industrial environments.
Key Benefit
1. Advanced Motor Protection
The electronic sensing technology ensures precise current monitoring, protecting motors against overload, phase imbalance, and ground faults more effectively than traditional thermal relays.
2. Adjustable Tripping Class (5–30)
This feature allows users to tailor the relay response to various motor types, including standard-duty and heavy-duty applications.
3. Compact and Space-Saving Design
Size S0 construction enables easy installation in compact control panels without compromising performance.
4. Flexible Reset Options
Supports both manual and automatic reset, providing operational flexibility and improved system uptime.
5. Internal Ground Fault Detection
Integrated ground fault monitoring adds an extra layer of safety, helping to prevent motor damage and electrical hazards.
Function
The Siemens 3RB3123-4NB0 operates by measuring the motor current via integrated current transformers. The electronic evaluation system processes these values and compares them to the set current.
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Overload Protection: Triggers if the current exceeds the set threshold for a duration determined by the selected trip class.
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Phase Failure Protection: Rapidly detects the loss of a phase to prevent unbalanced heating of the motor windings.
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Ground Fault Detection: Monitors for current leakage to earth, providing an extra layer of protection for the motor and cabling.
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Reset Modes: Features a flexible Manual/Automatic/Remote Reset selector, allowing for customized recovery protocols after a fault occurs.
Application
The Siemens 3RB3123-4NB0 Overload Relay is suitable for a wide range of industrial and commercial motor protection applications, including:
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Industrial motor control panels
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Conveyor systems
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Pumps and compressors
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HVAC systems
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Packaging machinery
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Automation and control systems
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Manufacturing and processing plants
This relay is especially recommended for applications where precise protection, reliability, and compact installation are essential.
Technical Highlight
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Current Range: 0.32 – 1.25 A
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Relay Type: Electronic overload relay
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Size: S0
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Tripping Class: Class 5 to Class 30
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Mounting Type: Contactor mounting
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Main Circuit Connection: Screw terminals
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Auxiliary Circuit Connection: Screw terminals
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Reset Type: Manual / Automatic
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Protection Features: Overload, phase failure, internal ground fault detection
Installation and Maintenance
Mounting the 3RB3123-4NB0 is straightforward. It features screw terminals for both the main circuit and the auxiliary circuit. The relay is designed for direct mounting onto S0 contactors, but standalone installation is also possible using separate mounting brackets. Maintenance is minimal; however, periodic testing of the “Test/Stop” function is recommended to ensure the auxiliary contacts are functioning correctly.
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