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What is a Safety Interlock Switch?

A Safety Interlock Switch is able to reliably monitor and protect protective guards, doors and covers.  Keys or coded actuators make the devices especially tamper-proof. Compliance with various standards makes the devices ideal for integration into machine development processes in line with international machinery safety requirements.

Eaton safety switches

How does a Safety Interlock Switch work?

safety interlock switch - non-contact interlock

Non-Contact interlock switch

Non-Contact interlock switches were specifically developed for monitoring protective covers such as doors, flaps and covers. The potential-free contacts are controlled by multiple magnets in the actuator, which makes the devices especially tamper-proof.  

The assembly comprises a sensor component and a separate magnet actuator component. The sensor is typically mounted to a stationary portion of a structure and the magnet to a movable portion. When the sensor and the actuator are within operating range, the NC contacts will be closed and the NO contacts will be open.

safety interlock switch - key interlock and limit swtches

Key Interlock and Safety Limit Switches

For Key Interlock and Safety Limit Switches, two different principles of operation ensure the mechanical securing action: magnetic-force interlocking (open-circuit principle) and spring-force interlocking (closed-circuit principle). 

Key Interlock switches are designed with two parts— the sensor and the actuator.  The sensor is typically mounted on the stationary portion of a structure and the actuator is mounted on the movable portion. The sensor is designed to work with the correct actuator (key) to reduce tampering and increase safety. 

Actuation of the interlock switch occurs only when the corresponding key is inserted into the key slot. The key is usually mounted on a door or machine guard in such a way that when the door or the guard is closed, the key fits into the slot actuating the switch. The special key design makes the safety interlock switch extremely difficult to defeat. When inserted into the slot, the key performs three separate mechanical functions.

LS-Titan miniature DIN IEC limit switch

Eaton’s LS-Titan limit switch line is a complete offering of safety position switches designed for worldwide application. Economical insulated plastic or rugged metal enclosures and modular, plug-in operating heads and bodies make the LS-Titan a flexible switching solution.

Safety Interlock Switch components

Key interlock switch

  • Switch body
    This part of the device contains the electrical contacts
  • Interlock keys
    Insert into the switch body to actuate the device
  • Connection interface
    An interlock switch may have internal wiring terminals and be equipped with a conduit or cable seal entry, or may come equipped with a factory installed cable, cordset, or built-in pin connector
Safety Interlock Switch components

Non-contact interlock switch

  • Interlock sensor
    This part of the device contains the electrical contacts that switch state when the coded magnet is placed in close proximity
  • Connection interface
    An interlock switch may be equipped with a factory installed cable or connectorized cordset
  • Coded magnet
    Creates a detection when placed in proximity to the Interlock Sensor
Non-Contact Interlock Switch

Why choose a safety interlock switch for a machine guarding application

  • Very robust and survivable
  • Immune to dirty, greasy adverse environmental conditions
  • Compliant with international standards
    • IEC 62061, up to SIL3
    • DIN EN ISO 13849, up to PLe
    • ISO 14119
    • IEC 60947-5-3
  • Outputs: 2 or 3 contacts
  • NO, NC, and multiple circuit combinations
  • Connection types including cable and M12 connector
  • B10d: 20,000,000
  • Reversible mounting
  • High misalignment tolerance
  • SIL 3 and PLe ratings
  • –10 °C to +55 °C temperature range
  • IP67, IP69K enclosure ratings

sensor on a conveyor

RS-Titan non-contact door interlock safety switches

RS safety interlock switches are designed specifically to monitor protective guards such as doors, flaps and hoods. All switches are safety-rated and use magnetically coded actuators to minimize defeat by simple magnets.

Variables to consider when selecting a safety interlock switch

Take into consideration the following variable when selecting a safety interlock switch

Location

Select the switch body size to physically fits in the application location

Key position and orientation

For keyed switches, determine the key position and orientation required for the mounting location and select the correct key

Actuator position and sensor orientation

For non-contact switches, determine the actuator position and sensor orientation required for the mounting location and select the correct device

Output configuration

Select the appropriate output configuration for the application based on the number of circuits needed

  • a Normally Open circuit turns on the output circuit when actuated
  • a Normally Closed circuit turns off the output circuit when actuated
  • Interlock switches are available with
    • Normally Open and 1 Normally Closed contacts
    • Normally Closed contacts
    • Normally Open and 2 Normally Closed contacts (non-contact switches only)

Wiring and connection requirements

Review wiring and connection requirements and select a sensor with the appropriate interface

What specialty Safety Interlock Switch types and features are important to understand?

SmartWire-DT versions of interlock switches are wired specially to connect directly to Eaton’s SmartWire-DT On Machine I/O products.  

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