Product Description

Siemens 3RB3123-4NB0 Electronic Overload Relay – 0.32–1.25 A, Class 5E–30E

The Siemens 3RB3123-4NB0 is a microprocessor-based electronic overload relay from the Siemens SIRIUS 3RB3 series, designed for motor protection in industrial automation and motor-control systems. The exact Siemens datasheet specifies an adjustable current range of 0.32 to 1.25 A, selectable trip classes 5E, 10E, 20E and 30E, S0 contactor mounting, and screw-terminal connections for both the main and auxiliary circuits.

The relay provides electronic overload protection along with phase-failure and asymmetry protection and activatable internal ground-fault detection. The 3RB31 family also provides manual/automatic reset, integrated electrical remote reset, TEST functionality, switch-position indication and self-monitoring.

Siemens SIRIUS 3RB3 Electronic Overload Relay

The 3RB3123-4NB0 belongs to the Siemens SIRIUS 3RB electronic overload relay family, designed to monitor motor current electronically and protect motors against overload and related abnormal operating conditions.

Its microprocessor-based design allows configurable trip characteristics and provides additional protection functions compared with basic thermal overload devices.

Typical applications include:

• Small industrial motors

• Pumps

• Fans and blowers

• Small compressors

• Conveyors

• Machine tools

• Production machinery

• Process equipment

• Industrial automation

• OEM control panels

Adjustable 0.32–1.25 A Current Range

The 3RB3123-4NB0 provides an adjustable current-setting range of 0.32 to 1.25 A. The official product datasheet confirms this range.

This makes the relay suitable for protecting motors with relatively low rated operating currents.

The current setting should be adjusted according to the motor nameplate current and the requirements of the complete motor-protection system.

Selectable Class 5E–30E

The relay supports four selectable trip classes:

• Class 5E

• Class 10E

• Class 20E

• Class 30E

Siemens identifies these trip classes as adjustable features of the 3RB31 electronic overload relay family.

This allows the protection characteristic to be selected according to the motor starting time and application requirements.

Electronic Overload Protection

The primary function of the 3RB3123-4NB0 is electronic protection against motor overload.

The relay continuously evaluates motor current and responds when the measured condition exceeds the configured overload characteristics.

This can help protect motors against:

• Prolonged overcurrent

• Excessive mechanical loading

• Motor overheating caused by overload

• Abnormal operating conditions

• Incorrectly selected starting characteristics

Correct current and trip-class settings are essential for effective motor protection.

Phase-Failure and Asymmetry Protection

The 3RB31 family provides phase-failure and asymmetry protection in addition to overload protection.

These functions are particularly useful for three-phase motors because phase abnormalities can result in unbalanced current and additional motor heating.

The relay therefore provides broader electronic motor protection than an overload-only device.

Internal Ground-Fault Detection

The 3RB3123-4NB0 includes activatable internal ground-fault detection as part of the 3RB31 protection functions.

This can provide additional monitoring for suitable motor-protection applications.

The complete electrical protection system should always be designed according to the specific installation requirements.

Manual, Automatic and Remote Reset

The Siemens 3RB31 family supports:

• Manual RESET

• Automatic RESET

• Integrated electrical remote RESET

These options allow the relay to be incorporated into different motor-control and automation strategies.

Manual reset can be used where operator intervention is required after a trip, while automatic or remote reset may be suitable for appropriately designed automated systems.

TEST Function and Self-Monitoring

The 3RB3123-4NB0 benefits from the 3RB31 family's TEST function, switch-position indication and self-monitoring capabilities.

These functions can assist with:

• Commissioning

• Troubleshooting

• Preventive maintenance

• Functional testing

• Control-panel servicing

1 NO + 1 NC Auxiliary Contacts

The 3RB3123-4NB0 has 1 normally open (NO) and 1 normally closed (NC) auxiliary contact. The Siemens datasheet identifies the NC contact for contactor disconnection and the NO contact for the "tripped" message.

These contacts can be used for:

• Contactor control

• Trip indication

• PLC feedback

• Alarm signalling

• Control-system interlocking

• Motor fault monitoring

Contactor Mounting

The 3RB3123-4NB0 is designed for contactor mounting and belongs to the S0 size range. The Siemens datasheet specifies a 45 mm width, 87 mm height and 84 mm depth.

This makes it suitable for integration with compatible Siemens SIRIUS contactors in compact motor-starter assemblies.

Screw-Terminal Connections

The 3RB3123-4NB0 uses screw-type terminals for both the main current circuit and auxiliary/control circuit. The auxiliary terminal is removable.

This provides a conventional wiring method for industrial panel builders and maintenance teams.

690 V Insulation Voltage

The exact product datasheet specifies an insulation voltage of 690 V and a 6 kV surge-voltage withstand rating.

These ratings should be considered together with the actual motor-control system, protective coordination and installation conditions.

Industrial Motor-Control Applications

The 3RB3123-4NB0 is suitable for various low-current motor-protection applications.

Small Pumps

It can protect compatible low-current pump motors against overload and phase-related abnormalities.

Fans and Blowers

The selectable trip class can be configured to suit the motor's starting characteristics.

Small Compressors

Electronic overload monitoring can help protect compressor motors against excessive current.

Conveyors

It can be incorporated into control systems for small conveyor motors.

Machine Tools

The relay can provide motor protection in compact machine-control panels.

Process Automation

Its electronic protection, auxiliary signalling and reset functions make it suitable for automated process equipment.

Suitable for OEMs and Panel Builders

The 3RB3123-4NB0 is suitable for OEM machine manufacturers, electrical panel builders, automation integrators and industrial maintenance professionals.

Its combination of 0.32–1.25 A adjustable current, Class 5E–30E selection, phase-failure and asymmetry protection, internal ground-fault detection, flexible reset functions and S0 contactor mounting makes it suitable for low-current industrial motor applications.

Key Features

• Siemens SIRIUS 3RB3 electronic overload relay

• Article number 3RB3123-4NB0

• Microprocessor-based electronic overload protection

• 0.32–1.25 A adjustable current range

• Class 5E, 10E, 20E and 30E adjustable

• Contactor mounting

• Size S0

• Screw terminals for main and auxiliary circuits

• 690 V insulation voltage

• Overload protection

• Phase-failure protection

• Phase-asymmetry protection

• Activatable internal ground-fault detection

• 1 NO + 1 NC auxiliary contacts

• Manual and automatic RESET

• Integrated electrical remote RESET

• TEST function

• Self-monitoring

• Switch-position indication

Benefits

• Microprocessor-based protection: Provides electronic current monitoring and configurable motor protection.

• 0.32–1.25 A range: Suitable for low-current motor applications.

• Class 5E–30E selection: Allows the protection characteristic to be matched to motor starting requirements.

• Phase protection: Helps detect phase failure and asymmetry.

• Ground-fault detection: Adds an additional monitoring function when activated.

• Flexible reset: Supports manual, automatic and remote-reset strategies.

• Diagnostic functions: TEST and self-monitoring assist commissioning and maintenance.

• Auxiliary signalling: 1 NO + 1 NC contacts provide control and trip-feedback functions.

• Contactor mounting: Supports compact SIRIUS motor-starter assemblies.

• Screw connections: Provides a familiar industrial wiring solution.

Why Choose Siemens 3RB3123-4NB0?

The Siemens 3RB3123-4NB0 is a compact electronic overload relay for low-current motor protection from 0.32 to 1.25 A.

Its Class 5E, 10E, 20E and 30E selectable trip characteristics allow the relay to be matched to different motor-starting conditions, while phase-failure and asymmetry protection provide additional monitoring. The 3RB31 family also includes activatable internal ground-fault detection, flexible reset functions, TEST functionality and self-monitoring.

With S0 contactor mounting, 1 NO + 1 NC auxiliary contacts and screw terminals, it is suitable for compact industrial motor starters, OEM equipment and automation panels.

Delivery Across India

SB Smart supplies Siemens industrial electrical and automation products across Faridabad, Gurgaon/Gurugram, Delhi NCR, Haryana, Noida, Punjab, Mumbai and major cities across India.

Major delivery locations include:

• Faridabad

• Gurgaon/Gurugram

• Delhi

• Delhi NCR

• Noida

• Greater Noida

• Haryana

• Punjab

• Mumbai

• Pune

• Ahmedabad

• Bengaluru

• Hyderabad

• Chennai

• Kolkata

• Jaipur

• Chandigarh

• Lucknow

• Indore

• Surat

• Vadodara

• Nagpur

• Coimbatore

• And other major cities across India

Frequently Asked Questions

1. What is Siemens 3RB3123-4NB0?

It is a Siemens SIRIUS 3RB3 microprocessor-based electronic overload relay for motor protection with a 0.32–1.25 A adjustable current range and Class 5E–30E selectable trip classes.

2. What is the current setting range?

The adjustable current range is 0.32–1.25 A.

3. Which trip classes are available?

The relay supports Class 5E, 10E, 20E and 30E.

4. Does it provide phase-failure protection?

Yes. The 3RB31 family provides phase-failure and asymmetry protection in addition to overload protection.

5. Does it have ground-fault detection?

Yes. Internal ground-fault detection is available as an activatable function.

6. How many auxiliary contacts does it have?

It provides 1 NO + 1 NC auxiliary contacts.

7. What reset options are available?

The 3RB31 family supports manual, automatic and integrated electrical remote RESET.

8. Is it contactor-mounted?

Yes. The 3RB3123-4NB0 is designed for S0 contactor mounting.

9. What type of terminals are used?

It uses screw-type terminals for the main and auxiliary/control circuits.

10. Where can I buy Siemens 3RB3123-4NB0 in India?

You can explore the Siemens industrial electrical and automation product range at SB Smart for electronic overload relays, motor-protection devices, contactors and related control components.