Product Description

Siemens 3RB3123-4SB0 Electronic Overload Relay – 3–12 A, Class 5E–30E

The Siemens 3RB3123-4SB0 is a microprocessor-based electronic overload relay from the Siemens SIRIUS 3RB3 series, designed for reliable motor protection in industrial automation and motor-control applications. It provides an adjustable current setting range of 3 to 12 A, selectable trip classes 5E, 10E, 20E and 30E, and S0 contactor mounting. Siemens identifies this exact article as an electronic overload relay for motor protection with screw terminals for both the main and auxiliary circuits.

Siemens SIRIUS 3RB3 Electronic Overload Relay

The 3RB3123-4SB0 belongs to the Siemens SIRIUS 3RB3 electronic overload relay family, which is designed to protect motors against overload and other abnormal operating conditions.

The microprocessor-based design provides electronic current monitoring and configurable trip characteristics, making the relay suitable for industrial motor starters and automation systems.

Typical applications include:

• Industrial motor control

• Pumps

• Fans and blowers

• Compressors

• Conveyors

• Machine tools

• Production machinery

• Process equipment

• Industrial automation

• OEM control panels

Adjustable 3–12 A Current Range

The 3RB3123-4SB0 has an adjustable current-setting range of 3 to 12 A. Siemens' official product data confirms this exact range.

This allows the overload relay to be adjusted according to the rated current of the motor being protected.

The current setting should be selected based on 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 specifies these trip classes as adjustable for the 3RB31 electronic overload relay family.

The selectable class allows the protection characteristic to be matched to different motor starting times and load conditions.

Electronic Overload Protection

The primary function of the 3RB3123-4SB0 is electronic protection against motor overload.

The relay monitors the motor current and trips when the measured operating 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

• Improperly selected motor starting characteristics

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

Phase-Failure and Asymmetry Protection

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

Phase-related abnormalities can cause unbalanced current and additional motor heating. Electronic monitoring therefore provides broader protection for three-phase motors.

This makes the 3RB3123-4SB0 suitable for industrial three-phase motor-control systems.

Internal Ground-Fault Detection

The 3RB31 family also provides activatable internal ground-fault detection. Siemens lists this as one of the protection and monitoring functions of the series, and the exact 3RB3123-4SB0 product description includes internal ground-fault detection.

This can provide an additional protection function in suitable motor applications.

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

Manual and Automatic Reset

The 3RB3123-4SB0 supports manual and automatic reset. Siemens identifies these reset modes for the exact product and the 3RB31 family.

This gives flexibility in motor-control applications where the relay may need either operator intervention or automatic resetting according to the control strategy.

The 3RB31 family also provides integrated electrical remote reset, allowing suitable automation systems to incorporate remote resetting.

TEST Function and Self-Monitoring

Siemens specifies the 3RB31 electronic overload relay family with a TEST function, switch-position indication and self-monitoring.

These functions can support:

• Commissioning

• Troubleshooting

• Preventive maintenance

• Functional testing

• Control-panel servicing

Self-monitoring can help identify certain internal operating conditions, while the TEST function supports functional verification.

1 NO + 1 NC Auxiliary Contacts

The 3RB31 series provides 1 normally open (NO) and 1 normally closed (NC) auxiliary contact.

These contacts can be incorporated into the motor-control circuit for:

• Contactor control

• Trip indication

• PLC feedback

• Alarm signalling

• Control-system interlocking

• Motor fault monitoring

This allows the overload relay to communicate its operating or trip state to the associated control system.

Contactor Mounting

The 3RB3123-4SB0 is designed for contactor mounting in Size S0. Siemens explicitly identifies the exact article as a Size S0 electronic overload relay with contactor mounting.

This enables integration into compatible SIRIUS motor-starter assemblies.

Its compact mounting arrangement is useful for:

• Motor starters

• Machine-control panels

• OEM control cabinets

• Industrial automation panels

• Pump and fan control systems

The exact compatible contactor should always be verified before installation.

Screw-Terminal Connections

The 3RB3123-4SB0 uses screw terminals for both the main and auxiliary circuits. Siemens specifies removable auxiliary/control terminals and screw-type connections for the product.

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

690 V Insulation Voltage

Siemens specifies an insulation voltage of 690 V for the exact product, with a 6 kV surge-voltage withstand rating.

These ratings are relevant when integrating the relay into industrial motor-control assemblies and should be considered together with the applicable system voltage and installation requirements.

Compact S0 Design

The 3RB3123-4SB0 is a Size S0 electronic overload relay. Siemens specifies dimensions of approximately 87 mm height, 45 mm width and 84 mm depth.

Its compact size is suitable for:

• Control cabinets

• Motor starters

• Automation panels

• Machine-control systems

• OEM electrical assemblies

Industrial Motor-Control Applications

The 3RB3123-4SB0 can be used in various industrial motor-protection applications.

Pumps

It can protect compatible pump motors against overload and phase-related abnormal conditions.

Fans and Blowers

The selectable trip class can be chosen according to the motor's starting and operating characteristics.

Compressors

Electronic overload protection can help protect compressor motors from excessive current and associated thermal stress.

Conveyors

The relay can protect conveyor motors against excessive mechanical loading and phase abnormalities.

Machine Tools

It can be integrated into motor-control assemblies used in industrial machine tools and production machinery.

Process Automation

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

Suitable for OEMs and Panel Builders

The 3RB3123-4SB0 is suitable for OEM machine manufacturers, electrical panel builders, automation integrators and industrial maintenance professionals.

Its combination of 3–12 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 a practical motor-protection solution.

Key Features

• Siemens SIRIUS 3RB3 electronic overload relay

• Article number 3RB3123-4SB0

• Microprocessor-based electronic overload protection

• 3–12 A adjustable current range

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

• Size S0

• Contactor mounting

• Screw terminals for main and auxiliary circuits

• 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

• 690 V insulation voltage

Benefits

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

• 3–12 A adjustable range: Suitable for motors within the specified current range.

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

• Phase protection: Helps detect phase failure and asymmetry conditions.

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

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

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

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

• Contactor mounting: Allows integration into compatible SIRIUS motor starters.

• Compact S0 size: Helps optimize control-panel space.

Why Choose Siemens 3RB3123-4SB0?

The Siemens 3RB3123-4SB0 is a flexible electronic overload relay for motor protection in the 3–12 A range.

Its Class 5E, 10E, 20E and 30E selectable trip characteristics allow the relay to be adapted to different motor starting conditions. It also combines overload, phase-failure and asymmetry protection with activatable internal ground-fault detection and flexible reset functions.

With S0 contactor mounting, 1 NO + 1 NC auxiliary contacts and screw terminals, it provides a compact solution for integrated industrial motor-starter and automation systems.

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 3RB3123-4SB0?

It is a Siemens SIRIUS 3RB3 electronic overload relay for motor protection with a 3–12 A adjustable current range and Class 5E–30E selectable trip classes.

2. What is the current setting range?

The adjustable current range is 3–12 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 phase-asymmetry protection in addition to overload protection.

5. Does it have ground-fault detection?

Yes. The exact product includes internal ground-fault detection, which is an activatable function in the 3RB31 family.

6. How many auxiliary contacts does it have?

The 3RB31 series provides 1 NO + 1 NC auxiliary contacts.

7. What reset options are available?

The relay supports manual and automatic reset, while the 3RB31 family also provides integrated electrical remote reset.

8. Is it contactor-mounted?

Yes. The 3RB3123-4SB0 is designed for S0 contactor mounting.

9. What type of terminals are used?

The product uses screw-type terminals for the main and auxiliary circuits.

10. Where can I buy Siemens 3RB3123-4SB0 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.