What Are Some Of The Common Interlock Switch Mechanisms



Interlock switches merge a moveable guard door with the hazard’s power source. On the opening of the guard door, the power gets isolated, which ensures the machine does not pose dangers when an operator needs access. These types of switches can be used in applications that have the following needs:


  • Equipment or machinery that needs frequent access or can potentially cause death or injury 
  • Attempts to beat the system by overriding the switch need to be prevented. 
  • Unmanaged process interruption or delayed stopping could cause death or injury 

Selection Parameters

Keep in mind the critical factors about your unique requirements when choosing an interlock switch. These elements include the environment, materials, and interlocking mechanisms. 

In conditions with high possibility of damage to the interlock, or where frequent access is needed, you should use a heavy-duty interlock switch mechanism. Switches can have mechanical failure systems like cam overrides which close the contacts even if the actuator is broken or removed. 

To improve security, you can install several switches on a door. Interlock switches are a popular type of safety switches, but misalignment can happen when fences or gates sag over time. 

Interlock Mechanisms


  • Keyed (Guard, Tongue-Style) Products 


These are mechanical interlocks where the actuator and switching element do not make up a design unit but are merged or parted during actuation. They can fit into the main edge of lift-off, hinged, or sliding machine guards and provide interlock identification of movement. These types of interlock switches typically leverage a solenoid which applies a precise voltage. 

  • Suitable for applications with lift-off, hinged, and sliding guards
  • Can be hard to clean them thoroughly 
  • Needs to stay aligned with the switch body’s entry hole 
  • Built to prevent cheating of the safety switch



  • Hinged interlocks 


These products are placed over a hinged guard’s pin, which opens with the operation’s positive method. Devices with a pre-bored actuator shaft permit the use of the hinge pin as the point of mounting. You can use solid actuator shifts as hinge pins for certain kinds of guards. 

  • Suitable for applications that provide access to the hinge center line
  • Not ideal for wide guard doors because of the small opening margin, which creates a gap and also because of weight



  • Manually-operated bolt interlocks


These interlocks can be retracted by hand and offer a time delay for machinery run-down. The bolt keeps the machine guard in position by locking it and runs the contact.  Its initial few turns open the contacts, but till the knob is repeatedly turned, the bolt does not become fully retracted. 

  • Magnetic force locking – the magnetic coil’s activation holds the guard closed
  • Spring force locking – spring force holds the guard closed



  • Contact Configuration


Positive-break contacts are NC (normally closed) electrical contacts that, on actuation, are opened by a mechanical, non-resilient drive mechanism. If there is a mechanical failure, like the breaking of a weld or spring, the contact point stays activated.

True spring-actuated interlock switches are not classified as positive-brake systems. Interlock switches with NO (normally open) contact pairs and pairs of changeover contacts can also be bought and used. Generally, changeover contacts are utilized in SPDT (single-pole double-throw) devices. 


  • Actuators


A built-in actuator tracks the movable components’ position. The actuator’s movement opens positively powered safety contacts. If the actuator is apart from the switch body, it closes the contacts when it is placed in the switch head. 


  • Materials


Stainless steel and aluminum are commonly used. Some applications need chemically-resistant steel. Whereas, in some cases, lightweight plastic is used. Similarly, for a robust material, glass-reinforced thermoplastic encasing is utilized. 


  • Other Factors


Electrical specs include maximum DC voltage, maximum AC voltage, and maximum current. Safety and security features include:

  • Tamper-resistant
  • Explosion-proof
  • Hermetically-sealed
  • Visual indicators
  • Emergency overrides

Products with integral control units can be utilized to monitor several switches. Devices with manual time delays continue equipment protection even after the turning off of machine controls. Some interlock switches are built with a rotating head for several entry points. Finally, mounting sizes differ. 

We suggest you get recommendations from a leading provider or experienced professionals about the best electrical solutions for your business needs, including interlock switches and automatic transfer switches



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