Why are mechanical and electrical interlocks used in certain motor control circuits?

Interlocking systems are used mainly where definite operating and sequential procedures are to be followed. Applications are generally where the safety of a person working on equipment is in danger by someone inadvertently turning on the equipment and thereby inflicting injury.

Another application for interlocking systems is for access control. A simple, robust system, requiring no power, can be installed disallowing access by unauthorised persons into various areas of buildings, factories, plants etcetera. The limitations of interlocks are boundless and applications for safety or other reasons exist in all areas of industry.