Product Description

Siemens 3RH2122-1KB40 Coupling Contactor Relay – 2 NO + 2 NC, 24 V DC

The Siemens 3RH2122-1KB40 is a SIRIUS 3RH2 coupling contactor relay designed for industrial automation, PLC interfacing and auxiliary control applications. It features 2 normally open (NO) and 2 normally closed (NC) contacts, a 24 V DC low-power consumption coil, an integrated suppressor diode and screw-terminal connections. Siemens currently lists the exact article as an active product and specifies it as suitable for PLC outputs.

Siemens SIRIUS 3RH2 Coupling Relay

The 3RH2122-1KB40 is an auxiliary contactor and coupling relay used for switching control and auxiliary circuits rather than high-power motor loads.

It can provide an interface between PLC outputs and downstream control circuits, while its multiple auxiliary contacts can support feedback, signalling and interlocking functions.

Typical applications include:

• PLC output interfacing

• Industrial automation

• Machine-control panels

• Auxiliary circuit switching

• Electrical interlocking

• Control-circuit logic

• Signalling systems

• Process automation

• OEM control panels

• Industrial control cabinets

Low-Power 24 V DC Coil

The 3RH2122-1KB40 uses a 24 V DC coil with an operating range of 0.7 to 1.25 × Us. Siemens specifies this model as suitable for PLC outputs and lists a coil power of approximately 2.8 W.

The low-power coil design makes the relay suitable for electronic control systems where efficient coil operation and compatibility with PLC outputs are important.

Integrated Suppressor Diode

A built-in suppressor diode is provided across the DC coil. This helps manage the voltage transient produced when the coil is de-energized and is useful when interfacing the relay with electronic control outputs.

This feature makes the relay particularly suitable for PLC-based control panels and other electronic automation systems.

2 NO + 2 NC Contacts

The 3RH2122-1KB40 provides a 2 NO + 2 NC auxiliary contact arrangement.

All four contacts are instantaneous, providing flexible switching paths for:

• PLC signal transfer

• Contactor control

• Status feedback

• Electrical interlocking

• Machine sequencing

• Auxiliary signalling

• Relay logic

• Control-system interfaces

Siemens identifies the contact configuration as 22E.

Screw-Terminal Connections

The relay uses screw-type terminals for its auxiliary and control circuits, providing a familiar wiring method for industrial panel builders and maintenance teams.

This makes it suitable for conventional control-panel wiring and straightforward commissioning and maintenance.

Compact S00 Design

The 3RH2122-1KB40 is a compact S00-size coupling contactor relay. Siemens lists dimensions of approximately 45 mm width, 57.5 mm height and 73 mm depth, making it suitable for space-conscious control cabinets.

It supports screw and snap-on mounting on a 35 mm standard mounting rail.

Suitable for PLC Outputs

A major application advantage of the 3RH2122-1KB40 is its suitability for PLC output circuits.

It can be used as a coupling interface between a PLC and external auxiliary circuits, allowing the PLC to control downstream devices through the relay contacts.

Typical applications include:

• PLC-driven contactor control

• Auxiliary actuator interfaces

• Machine sequencing

• Industrial signalling

• Interlocking circuits

• Control-panel automation

The PLC output module should always be checked for compatibility with the relay's 24 V DC coil characteristics.

Non-Expandable Auxiliary Configuration

Siemens specifies this article as not expandable with an additional auxiliary switch. The integrated 2 NO + 2 NC contact arrangement therefore represents the available auxiliary contact configuration of the device.

Industrial Automation Applications

The 3RH2122-1KB40 can be used in a wide range of industrial automation systems.

PLC Interface

It can provide a switching interface between PLC outputs and auxiliary circuits.

Machine Control

The 2 NO + 2 NC arrangement can support different control, signalling and interlocking functions within machine sequences.

Motor-Control Panels

The relay can be used for auxiliary contactor control, feedback and interlocking around motor starters.

Process Automation

It can provide switching interfaces for process-control commands and auxiliary equipment.

OEM Control Panels

Its compact S00 size, low-power 24 V DC coil and DIN-rail mounting make it suitable for standardized OEM control-panel designs.

Suitable for OEMs and Panel Builders

The 3RH2122-1KB40 is suitable for OEM machine manufacturers, electrical panel builders, automation integrators and industrial maintenance professionals.

Its combination of low-power 24 V DC coil, integrated suppressor diode, 2 NO + 2 NC contacts, PLC compatibility and screw terminals makes it a practical coupling relay for modern industrial control systems.

Key Features

• Siemens SIRIUS 3RH2 coupling contactor relay

• Article number 3RH2122-1KB40

• 2 NO + 2 NC instantaneous contacts

• 24 V DC coil

• Low-power consumption coil

• Integrated suppressor diode

• Screw-terminal connections

• Size S00

• Suitable for PLC outputs

• Not expandable with auxiliary switch

• DIN-rail compatible

• Suitable for auxiliary circuit switching

• Suitable for industrial automation

• Suitable for OEM control panels

Benefits

• Low-power 24 V DC coil: Suitable for PLC and electronic control outputs.

• 2 NO + 2 NC contacts: Provides multiple switching paths for control and monitoring.

• Integrated suppressor diode: Helps reduce coil-related voltage transients.

• PLC-compatible: Designed for suitable PLC output applications.

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

• Screw terminals: Provides a familiar industrial wiring method.

• DIN-rail mounting: Supports practical electrical-panel installation.

• Flexible control logic: Suitable for signalling, feedback and interlocking applications.

Why Choose Siemens 3RH2122-1KB40?

The Siemens 3RH2122-1KB40 combines a 24 V DC low-power coil, integrated suppressor diode and 2 NO + 2 NC auxiliary contacts in a compact S00 coupling relay.

Its suitability for PLC outputs, screw-terminal connections and DIN-rail mounting makes it a practical interface component for industrial automation panels, OEM machines and control cabinets. Siemens currently lists the exact article as an active product.

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 3RH2122-1KB40?

It is a Siemens SIRIUS 3RH2 coupling contactor relay with 2 NO + 2 NC contacts and a 24 V DC low-power coil.

2. How many contacts does it have?

It has 2 normally open and 2 normally closed instantaneous contacts.

3. What is the coil voltage?

The rated coil voltage is 24 V DC.

4. Does it have a suppressor diode?

Yes. It has an integrated suppressor diode.

5. Is it suitable for PLC outputs?

Yes. Siemens specifically specifies the 3RH2122-1KB40 as suitable for PLC outputs.

6. Does it use screw terminals?

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

7. What size is the relay?

It is a compact S00-size coupling relay.

8. Can an additional auxiliary contact block be attached?

No. Siemens specifies this article as not expandable with an auxiliary switch.

9. Where can the 3RH2122-1KB40 be used?

It can be used in PLC interfaces, industrial automation, machine-control panels, auxiliary switching, interlocking and OEM control cabinets.

10. Where can I buy Siemens 3RH2122-1KB40 in India?

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