Interlocking two contactors in electrical systems is a technique used to prevent two or more contactors from being energized at the same time.
Connections such as Forward/Reverse motors connections, star/delta motor connections, automatic changeover switch connections, and any electrical connection(s) that require different electrical systems to operate at different times.
there are two types of interlocking contactors, namely: Electrical interlock and mechanical interlock.
This video gives a detailed explanation, making use of practical wiring and drawings to help you clearly understand how to effectively interlock magnetic contactors electrically.

You may also watch the recommended videos below.
   • STAR DELTA CONNECTION  
   • 3PHASE MOTOR TESTING WITH MULTIMETER  
   • #1 Contactors explained | How contact...  
   • Complete wiring | Automatic changeove...  
   • how to build 3phase automatic change...  
   • how to build 3phase automatic change...  
   • HOW TO WIRE AN 8PIN TIMER FOR |"ON DE...  
   • HOW TO WIRE A TIMER TO A CONTACTOR  
   • how to connect 3phase motor in star o...  
   • Forward and reverse motor control com...  
   • 3phase motor winding connection at th...  
   • How to check for open circuit in elec...  
   • HOW TO WIRE D.O.L STARTER  PART2  |PO...