What is INTERLOCKING and what are the purpose

Electrical and Mechanical Interlock are used when there two
or more source of power supply to a common load.

For example a Power Utility Electric supply and a standby
Generator power supply. Of course we do not want this two
supply to be connected to the load, not unless properly
synchronize, as the smaller Power supply will get motorize
and eventually be burnt. Usually in the case of smaller size
of Standby generator which is being normally protected by a
electrical and mechanical interlocking device.

Electrical interlocking device like (ACB) Air Circuit or 
Breaker and Mechanical   Interlocking device is a mechanical
way, bolt or metal strips, design so as not to switch on the
two ACB power supply source at the same time. You can only
switch on one breaker at a time. This will avoid the
Electrical Fault cause by two power source simultaneously
supplying common load.

The safest way is to use both Electrical and Mechanical
interlock on multi source op power supply.

The 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.