Product Description

Siemens 3RH2131-1BB408K Contactor Relay – Mechanically Linked Contacts, 3 NO + 1 NC

The Siemens 3RH2131-1BB408K is an auxiliary contactor / contactor relay from the Siemens SIRIUS 3RH2 series, designed for industrial control, automation, signalling and interlocking applications. The corresponding Siemens article 3RH2131-1BB40 is specified with 3 NO + 1 NC contacts, a 24 V DC coil, screw terminals and compact S00 frame size. Siemens currently lists this product as an active SIRIUS 3RH2 contactor relay.

Siemens SIRIUS 3RH2 Contactor Relay

The 3RH2131-1BB408K is designed for switching auxiliary and control circuits rather than directly switching high-power motor loads.

As an auxiliary contactor, it can be used to transfer control signals, provide feedback and implement electrical interlocking within industrial automation systems.

Typical applications include:

• Industrial automation

• Machine-control panels

• Motor-control circuits

• PLC interface circuits

• Electrical interlocking

• Signalling systems

• Process automation

• OEM machinery

• Control cabinets

• Auxiliary switching

Mechanically Linked Contact Elements

A key feature of the specified product is its mechanically linked contact elements.

Mechanically linked contacts maintain a defined mechanical relationship between the switching elements, making them suitable for control circuits where the contact states need to be monitored reliably.

This can be useful for:

• Interlocking circuits

• Contactor status monitoring

• PLC feedback

• Machine sequencing

• Control logic

• Diagnostic circuits

• Safety-related control architectures where the complete system is designed accordingly

The complete control and safety function must always be designed according to the applicable machine and electrical requirements.

3 NO + 1 NC Contact Configuration

The 3RH2131-1BB40 configuration provides 3 normally open (NO) and 1 normally closed (NC) contacts. Siemens identifies the device as a four-pole S00 contactor relay with a 31E contact arrangement.

This arrangement provides multiple auxiliary switching paths for:

• Contactor feedback

• PLC inputs

• Electrical interlocking

• Relay logic

• Machine sequencing

• Status signalling

• Control-system feedback

The contacts should be used within their specified electrical ratings.

24 V DC Coil

The 3RH2131-1BB408K uses a 24 V DC control coil. Siemens' corresponding article data confirms the 24 V DC control voltage.

This makes the relay suitable for industrial control systems using 24 V DC control circuits, including compatible PLC and automation architectures.

The control voltage must always be matched with the product marking before installation.

Screw-Terminal Connections

The product uses screw terminals, providing a conventional connection method for industrial control-panel wiring. Siemens specifies screw-terminal construction for the 3RH2131-1BB40.

This connection method is familiar to panel builders and maintenance teams and supports practical installation and servicing.

Compact S00 Design

The 3RH2131-1BB40 is a Size S00 contactor relay. Siemens' product data identifies the compact S00 frame size and a package width of approximately 50 mm.

The compact design is suitable for:

• Control cabinets

• Automation panels

• Machine-control stations

• OEM equipment

• Relay and contactor assemblies

Industrial Automation Integration

The 3RH2131-1BB408K can be integrated into industrial control systems alongside:

• PLCs

• HMIs

• Motor contactors

• Overload relays

• Circuit breakers

• Pushbuttons

• Selector switches

• Sensors

• Safety components

• Other Siemens SIRIUS devices

The NO and NC contacts can provide multiple control and feedback functions within the same control circuit.

Applications

The Siemens 3RH2131-1BB408K can be used for:

• Industrial automation

• Motor-control panels

• Auxiliary contactor circuits

• PLC signal interfacing

• Electrical interlocking

• Machine sequencing

• Production machinery

• Process automation

• Conveyor-control systems

• Pump-control circuits

• OEM control panels

• Industrial signalling

For related Siemens industrial electrical and automation products, customers can explore the Siemens product range at SB Smart.

Suitable for OEMs and Panel Builders

The 3RH2131-1BB408K is suitable for OEM machine manufacturers, electrical panel builders, automation integrators and industrial maintenance professionals.

Its combination of mechanically linked contacts, 3 NO + 1 NC configuration, 24 V DC coil, screw terminals and S00 compact design makes it suitable for control and signalling applications where reliable auxiliary switching is required.

Key Features

• Siemens SIRIUS 3RH2 contactor relay

• Article number 3RH2131-1BB408K

• Mechanically linked contact elements

• 3 NO + 1 NC contacts

• 24 V DC coil

• Screw terminals

• Size S00

• Four-pole auxiliary contactor

• Suitable for electrical interlocking

• Suitable for PLC feedback

• Suitable for machine sequencing

• Suitable for industrial automation

• Suitable for OEM control panels

Benefits

• Mechanically linked contacts: Supports reliable contact-state relationships for suitable monitoring and control applications.

• 3 NO + 1 NC configuration: Provides multiple auxiliary switching paths.

• 24 V DC coil: Suitable for common industrial DC control architectures.

• Screw terminals: Provides a familiar industrial wiring method.

• Compact S00 size: Helps optimize control-panel space.

• Flexible control logic: Supports feedback, interlocking, signalling and machine sequencing.

• Automation integration: Suitable for PLC-based control systems.

• OEM-friendly: Suitable for standardized machine-control panel designs.

Why Choose Siemens 3RH2131-1BB408K?

The Siemens 3RH2131-1BB408K provides a compact auxiliary-contact switching solution for industrial automation and control systems.

Its mechanically linked contact elements, 3 NO + 1 NC configuration and 24 V DC coil make it suitable for applications requiring reliable auxiliary switching, interlocking and status feedback. The corresponding Siemens 3RH2131-1BB40 is currently listed as an active product in the SIRIUS 3RH2 contactor-relay family.

For OEMs, panel builders and automation integrators, it provides a practical solution for control circuits where multiple auxiliary contacts are required in a compact S00 device.

Delivery Across India

SB Smart supplies Siemens industrial electrical and automation products across Faridabad, Gurgaon/Gurugram, Delhi NCR, Haryana, Noida, Punjab, Mumbai and all 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 3RH2131-1BB408K?

It is a Siemens SIRIUS 3RH2 auxiliary contactor/contact relay with mechanically linked contacts, 3 NO + 1 NC contacts and a 24 V DC coil.

2. What is the contact configuration?

It provides 3 normally open and 1 normally closed contacts.

3. What is the coil voltage?

The corresponding Siemens article uses a 24 V DC coil.

4. Does it use screw terminals?

Yes. The relay uses screw-terminal connections.

5. What size is the contactor relay?

It is a compact S00-size contactor relay.

6. What are mechanically linked contacts used for?

They can support contact-state monitoring, interlocking, diagnostic and suitable safety-related control functions when incorporated into a correctly designed system.

7. Can it be used with a PLC?

Yes. Its auxiliary contacts can be incorporated into suitable PLC feedback and control circuits.

8. Does it switch high-power motor loads directly?

It is an auxiliary contactor/contact relay intended primarily for control and auxiliary circuits rather than direct high-power motor switching.

9. Where can the 3RH2131-1BB408K be used?

It can be used in industrial automation, machine-control panels, motor-control circuits, PLC interfaces, interlocking systems and OEM control cabinets.

10. Where can I buy Siemens 3RH2131-1BB408K in India?

You can explore the Siemens product range at SB Smart for Siemens contactor relays, auxiliary contact blocks, contactors and other industrial automation products.