Safety interlocking devices

For the electrical power distribution,we used a switch gears to control our distribution power supply to user.One of important things when design the system,we must include with safety interlocking device.

Motor control design also need to attach with interlocking system to ensure the operation is safe for user and can prevent for serious damage of equipment.

Before we design the control circuit or operation sequence,the important aspect that we should consider is about interlocking and must have a deep study to make sure it function properly.

Types of interlocking method

Normally in industry,interlocking devices have a two (2) types of method such as electrical and mechanical control.Their main purposes for interlocking system are  :

  • Automatically ‘Trip’ the switching device while it is carrying over load or fault current.
  • To prevent the switching mechanism from being ‘on’ position during set ‘off’ position.
  • Opening of access doors or panels before setting the switching device in its ‘off’ position.
  • To isolated the access by human operators while the system energized.
  • To avoid easy access to the bus bars when the switching devices in ON position
  • To prevent earthing switches from being closed on to live circuits or bus bars.
  • Incorrect electrical operation of a complex process system in which various external devices,motors or pumps are intimately related.
  • To avoid pump or electrical motor operate or  running other than their sequence accidentally


Mechanical interlocking device

We can used a mechanical device such as castle keys,levers,limit switch,latches,bolt and shutters to interlocking the system.For example a lubrication oil pump must be running before the machine driven motor is started for operation.

For switchgear likes Vacuum circuit breaker (VCB)  or Air circuit breaker (ACB),commonly used a mechanical interlocking system.Normally it use a levers and shutter to disconnect from bus bars or to avoid energized accidentally during OFF position.

Electrical  interlocking device

In automation industry,the famous devices for electrical interlocking are using Relays,Sensor,PLC, or electronic logic. Electrical interlocking is also used to ensure that certain closing and tripping functions take place in a particular sequence.

During engineer design the circuit control,they must include the interlocking device.It is the one of major items for electrical control panel.


  1. katy pavers says:

    katy pavers

    Safety interlocking devices – Electrical Engineering Centre

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