Switches guard locking, with

Fig. 13.11 Example of tongue-operated interlocking switch with guard locking, with actuator both out of and inserted in the body of the switch.

Interlocking mechanisms may be divided into those which lock the guard with the source of power, and those which lock with respect to the motion itself. BS 5304 1988 reviews different power and control interlocks. The methods described may be used separately or in combination to achieve an effective interlocking system. Typical elements of interlocking systems are considered below, but it must be appreciated that the effectiveness is as dependent on the integrity of the control circuit - whether electrical, pneumatic, hydraulic, etc. - as on the switch arrangement itself. For normal safe operation, the electrical circuit is complete, or pneumatic/hydraulic circuits are pressurised actuation of the interlock either breaks the electrical circuit or exhausts the pneumatic/hydraulic circuits. 

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