Access Control Our access interlocks are used to reduce risk when workers enter hazardous areas. Their purpose is to eliminate the possibility of energy restoration occurring whilst personnel are in the restricted area. They achieve this by trapping the key that controls the electrical supply once the supply is off. Castell access interlocks have two parts; a main body, mounted to the stationary portion of the equipment or door frame, and a bolt, mounted to the door or gate. The key is always trapped in the main body of the interlock when the two parts are separated. Only once the bolt re-engages the main body will the key be released.