The Siemens 3RH2122-1BF408K is a SIRIUS 3RH2 auxiliary contactor / contactor relay designed for industrial control, automation, signalling and interlocking applications. It features mechanically linked contact elements, 2 normally open (NO) and 2 normally closed (NC) contacts, a 110 V DC coil, screw-terminal connections and a compact S00 frame size. Siemens' official data for the corresponding 3RH2122-1BF40 configuration confirms this exact contact arrangement, control voltage, connection type and S00 size.
The 3RH2122-1BF408K is intended for switching auxiliary and control circuits rather than directly switching high-power motor loads.
It can be used to transfer control signals, provide feedback and implement interlocking functions in industrial electrical and automation systems.
Typical applications include:
Industrial automation
Machine-control panels
PLC interface circuits
Motor-control circuits
Electrical interlocking
Signalling systems
Process automation
OEM machinery
Control cabinets
Auxiliary switching
A key feature of the 3RH2122-1BF408K is its mechanically linked contact elements.
Mechanical linkage helps maintain a defined relationship between the contact elements, making the relay suitable for control circuits where the contact state needs to be monitored reliably.
Potential applications include:
Contactor status monitoring
Electrical interlocking
PLC feedback
Machine sequencing
Diagnostic circuits
Control logic
Suitable safety-related control architectures
For safety-related applications, the complete safety function must be designed and validated as part of the overall machine-control system.
The 3RH2122-1BF40 configuration provides 2 normally open and 2 normally closed contacts. Siemens identifies this as a 22E contact arrangement.
This combination gives flexibility for different auxiliary control functions, including:
Contactor feedback
PLC inputs
Electrical interlocking
Relay logic
Machine sequencing
Status signalling
Auxiliary switching
Control-system feedback
The contacts should always be operated within their applicable electrical ratings.
The 3RH2122-1BF408K uses a 110 V DC control coil. Siemens' official data identifies the control supply as DC with a rated value of 110 V.
This makes the relay suitable for compatible industrial DC control systems.
The control voltage must always be matched with the exact product marking and electrical design before energizing the relay.
The 3RH2122-1BF408K uses screw-terminal connections, providing a conventional wiring method for industrial control panels. Siemens confirms the screw-terminal configuration for the corresponding 3RH2122-1BF40 article.
This is convenient for panel builders and maintenance teams working with traditional control-circuit wiring.
The relay is a Size S00 device. Its compact format makes it suitable for electrical cabinets where efficient use of panel space is important. Siemens' data confirms the S00 frame size.
It can be integrated into:
Control cabinets
Automation panels
Machine-control stations
OEM equipment
Relay and contactor assemblies
The 3RH2122-1BF408K can be integrated with:
PLCs
HMIs
Motor contactors
Overload relays
Circuit breakers
Pushbuttons
Selector switches
Sensors
Safety components
Other Siemens SIRIUS devices
Its 2 NO + 2 NC contact configuration allows multiple control, feedback and interlocking functions from a single compact relay.
The Siemens 3RH2122-1BF408K can be used for:
Industrial automation
Motor-control panels
PLC signal interfacing
Electrical interlocking
Machine sequencing
Production machinery
Process automation
Conveyor-control systems
Pump-control circuits
OEM control panels
Industrial signalling
Auxiliary switching
For related Siemens industrial electrical and automation products, customers can explore the Siemens product range at SB Smart.
The 3RH2122-1BF408K is suitable for OEM machine manufacturers, electrical panel builders, automation integrators and industrial maintenance professionals.
Its combination of mechanically linked contacts, 2 NO + 2 NC configuration, 110 V DC coil, screw terminals and compact S00 design makes it suitable for control and signalling applications where reliable auxiliary switching is required.
Siemens SIRIUS 3RH2 contactor relay
Article number 3RH2122-1BF408K
Mechanically linked contact elements
2 NO + 2 NC contacts
110 V DC coil
Screw terminals
Size S00
22E contact arrangement
Suitable for electrical interlocking
Suitable for PLC feedback
Suitable for machine sequencing
Suitable for industrial automation
Suitable for OEM control panels
Mechanically linked contacts: Supports reliable contact-state relationships for suitable monitoring and control applications.
2 NO + 2 NC contacts: Provides multiple auxiliary switching paths.
110 V DC coil: Suitable for compatible industrial DC control systems.
Screw terminals: Provides a familiar industrial wiring method.
Compact S00 size: Helps optimize control-panel space.
Flexible control logic: Supports feedback, interlocking, signalling and sequencing.
Automation integration: Suitable for PLC-based control systems.
OEM-friendly: Suitable for standardized machine-control panel designs.
The Siemens 3RH2122-1BF408K combines mechanically linked contact elements, 2 NO + 2 NC contacts, a 110 V DC coil and screw-terminal connections in a compact S00 auxiliary contactor.
The corresponding 3RH2122-1BF40 is confirmed by Siemens as a 2 NO + 2 NC, 110 V DC, screw-terminal, S00 contactor relay.
This makes the relay suitable for industrial automation systems requiring auxiliary switching, feedback, interlocking and control functions.
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 NCR, Noida, Haryana, Punjab, Mumbai, Pune, Ahmedabad, Bengaluru, Hyderabad, Chennai, Kolkata, Jaipur, Chandigarh, Lucknow, Indore, Surat, Vadodara, Nagpur, Coimbatore and other major cities across India.
It is a Siemens SIRIUS 3RH2 auxiliary contactor/contact relay with mechanically linked contacts, 2 NO + 2 NC contacts and a 110 V DC coil.
It provides 2 normally open and 2 normally closed contacts.
The specified control coil is 110 V DC.
Yes. The product uses screw-terminal connections.
It is a compact S00-size contactor relay.
They can support contact-state monitoring, interlocking, diagnostics and suitable safety-related control functions within a correctly designed system.
Yes. Its auxiliary contacts can be incorporated into suitable PLC feedback and control circuits, provided the electrical ratings are compatible.
It is an auxiliary contactor/contact relay, intended primarily for control and auxiliary circuits rather than direct high-power motor switching.
It can be used in industrial automation, machine-control panels, PLC interfaces, interlocking systems, production machinery and OEM control cabinets.
You can explore the Siemens product range at SB Smart for Siemens contactor relays, auxiliary contact blocks, contactors and other industrial automation products.
| Specification | Details |
|---|---|
| Product Name | Auxiliary Contactor Relay |
| Manufacturer | Siemens |
| Brand | Siemens |
| Series | SIRIUS 3RH2 |
| Model Number | 3RH2122-1BF408K |
| SKU | 3RH2122-1BF408K |
| Product Type | Auxiliary Contactor |
| Frame Size | S00 |
| Contact Configuration | 2NO + 2NC |
| Number of Normally Open Contacts | 2 |
| Number of Normally Closed Contacts | 2 |
| Contact Design | Mechanically Linked Contact Elements |
| Coil Voltage | 110V DC |
| Control Voltage Type | DC |
| Connection Type | Screw Terminals |
| Mounting Type | DIN Rail / Panel Mount |
| Rated Operational Current AC-12 | 10 A |
| Rated Operational Current AC-15 (230V) | 10 A |
| Rated Operational Current AC-15 (400V) | 3 A |
| Rated Operational Current AC-15 (500V) | 2 A |
| Rated Operational Current AC-15 (690V) | 1 A |
| Rated Insulation Voltage (Ui) | 690 V |
| Rated Impulse Withstand Voltage (Uimp) | 6 kV |
| Mechanical Endurance | Up to 30 Million Operations |
| Degree of Protection | IP20 |
| Operating Temperature | -25°C to +60°C |
| Storage Temperature | -55°C to +80°C |
| Width | 45 mm |
| Height | 57.5 mm |
| Depth | 73 mm |
| Standards Compliance | IEC 60947-1, IEC 60947-4-1, IEC 60947-5-1 |
| Applications | Automation, Interlocking, Signaling & Control |
| Product Family | Siemens SIRIUS Auxiliary Contactors |
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