Siemens 3SE51120BA008K Basic Switch – 3SE51 Metal Enclosure, 1 NO + 1 NC Slow-Action Contacts

The Siemens 3SE51120BA008K is a SIRIUS 3SE51 basic switch for position-switch applications, designed for industrial machinery, mechanical position monitoring, limit detection, and machine-control applications. It features a metal enclosure according to EN 50041, 1 × M20 × 1.5 device connection, and 1 NO + 1 NC slow-action contacts. The switch is supplied without an actuator head, allowing a compatible actuator to be selected separately according to the mechanical requirements of the application. Siemens lists the corresponding 3SE5112-0BA00 configuration with these same core characteristics.

What Is Siemens 3SE51120BA008K Used For?

The 3SE51120BA008K basic switch acts as the switching unit within a mechanical position-switch assembly. When fitted with a suitable compatible actuator, it can detect the position or movement of a machine component and provide an electrical switching signal to the appropriate control circuit.

It can be used for:

• Machine position monitoring
• Mechanical limit detection
• End-position detection
• Conveyor systems
• Packaging machinery
• Machine tools
• Production equipment
• Material-handling systems
• Industrial automation
• Machine sequencing
• Mechanical interlocking
• Position-dependent control

Key Features & Benefits

• Siemens SIRIUS 3SE51 basic switch
• Model 3SE51120BA008K
• Metal enclosure according to EN 50041
• 1 × M20 × 1.5 device connection
• 1 NO + 1 NC slow-action contacts
• Supplied without actuator head
• Suitable for compatible actuator selection
• Suitable for industrial position-switch applications
• Suitable for OEM machinery
• Suitable for maintenance and replacement applications
• Designed for mechanical position monitoring
• Suitable for machine-control applications

The Siemens product information for 3SE5112-0BA00 confirms the metal EN 50041 enclosure, M20 × 1.5 connection, 1 NO/1 NC slow-action contacts, and absence of an actuator head.

1 NO + 1 NC Slow-Action Contacts

The 3SE51120BA008K provides one normally open (NO) and one normally closed (NC) contact.

Unlike a quick-action version, this configuration uses slow-action contacts, where the contact movement follows the mechanical movement of the actuator.

This arrangement can be useful for appropriate machine-control and position-monitoring circuits, including:

• Position indication
• Limit monitoring
• PLC input signaling
• Machine sequencing
• Control interlocking
• Machine-status monitoring
• Mechanical position detection

The corresponding Siemens 3SE5112-0BA00 product data confirms 1 NO and 1 NC contacts with the slow-action switching principle.

Supplied Without Actuator Head

A major feature of the 3SE51120BA008K is that it is supplied without an actuator head.

This gives machine builders the flexibility to select a compatible actuator separately according to the machine's mechanical arrangement.

Depending on the application, the complete position-switch assembly may use an appropriate:

• Plunger actuator
• Roller actuator
• Lever actuator
• Rod actuator
• Other compatible actuator configuration

The correct actuator should be selected based on the required movement, travel, direction of actuation, mounting arrangement, and application.

Always verify actuator compatibility with the exact Siemens 3SE51 basic switch before ordering or installation.

Metal Enclosure According to EN 50041

The 3SE51120BA008K uses a metal enclosure according to EN 50041.

The corresponding Siemens 3SE5112-0BA00 product family is identified as an enclosure width of 40 mm according to EN 50041.

The metal construction provides a robust housing for suitable industrial machinery and position-switch installations.

This standardized format makes it suitable for applications where a compact industrial mechanical switch is required.

1 × M20 × 1.5 Device Connection

The switch provides 1 × M20 × 1.5 device connection.

This provides a standard metric connection point for routing the electrical cable into the position-switch housing.

Suitable cable glands and wiring accessories should be selected according to the installation environment and required protection level.

Proper cable-entry installation is important for maintaining reliable electrical connections and the intended enclosure protection.

Slow-Action Switching

The slow-action contact mechanism follows the movement of the actuator more directly than a snap-action mechanism.

This can be advantageous in applications where the switching sequence needs to correspond closely with the mechanical movement of the actuator.

The slow-action configuration can therefore be considered for suitable:

• Mechanical limit monitoring
• Machine-position detection
• Travel monitoring
• Machine sequencing
• Industrial control applications

The actual switching behavior depends on the selected compatible actuator and the mechanical arrangement of the complete position switch.

Modular 3SE51 Position-Switch Design

The 3SE51 platform provides a modular approach to mechanical position detection.

With the 3SE51120BA008K, the basic switching unit is supplied without an actuator head. This allows the machine designer to choose a compatible actuator based on the physical requirements of the equipment.

This is particularly useful for OEMs designing different machine variants where the required actuator arrangement may vary while the basic switching platform remains standardized.

Typical Industrial Applications

The Siemens 3SE51120BA008K basic switch can be used in:

• Industrial machinery
• Conveyor systems
• Packaging machines
• Machine tools
• Production lines
• Manufacturing equipment
• Material-handling systems
• Automated machinery
• Mechanical limit monitoring
• Machine travel detection
• Machine sequencing
• Industrial automation
• Position-dependent control

Benefits for OEM Machine Builders

For OEM machine builders, the 3SE51120BA008K provides a flexible basic switching platform for mechanical position detection.

The combination of an EN 50041 metal enclosure, 1 × M20 × 1.5 connection, and 1 NO + 1 NC slow-action contacts provides a practical configuration for industrial machinery.

The absence of a fixed actuator allows the machine builder to select the appropriate compatible actuator according to the machine's mechanical layout.

This can help standardize the switching unit across different machine models while allowing different actuator configurations where required.

Benefits for Maintenance and Replacement

The basic-switch configuration can also be useful for maintenance and replacement applications involving compatible Siemens 3SE51 position-switch assemblies.

Before selecting the product, verify:

• Complete Siemens order number
• 3SE51 compatibility
• EN 50041 enclosure format
• Contact configuration
• Slow-action switching
• M20 × 1.5 connection
• Actuator compatibility
• Mounting arrangement
• Electrical requirements
• Environmental requirements

Matching these characteristics can help ensure that the replacement component is appropriate for the existing machine.

Safety Considerations

Siemens documentation identifies the corresponding 3SE5112-0BA00 basic switch as suitable for use as a safety switch and specifies positive opening for the relevant configuration.

However, a basic switch by itself does not constitute a complete machine safety system. Where it is incorporated into a safety-related function, the complete safety architecture—including suitable safety controllers or relays, protective devices, wiring, monitoring, and risk assessment—must be properly designed and validated.

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Frequently Asked Questions

Q1. What is Siemens 3SE51120BA008K?

The 3SE51120BA008K is a Siemens SIRIUS 3SE51 basic switch for position-switch applications with an EN 50041 metal enclosure, 1 × M20 × 1.5 device connection, and 1 NO + 1 NC slow-action contacts.

Q2. Does it include an actuator head?

No. It is supplied without an actuator head.

Q3. What type of contacts does it have?

It has 1 NO + 1 NC slow-action contacts.

Q4. What enclosure standard does it use?

The corresponding Siemens configuration uses a metal enclosure according to EN 50041.

Q5. What type of device connection does it have?

It has 1 × M20 × 1.5 device connection.

Q6. What is the difference between slow-action and quick-action versions?

In a slow-action design, the contact movement follows the mechanical actuator movement more directly. A quick-action or snap-action mechanism provides a more defined switching transition.

Q7. Can an actuator be selected separately?

Yes. The product is supplied without an actuator head, so a compatible actuator can be selected according to the mechanical requirements.

Q8. Where can it be used?

It can be used for machine position monitoring, mechanical limit detection, conveyors, packaging machinery, machine tools, production equipment, material handling, and industrial automation.