bolt 18 of a monitoring switch 7 the actuating bolts 18 and 22 move parallel however in opposite direction to each other in the embodiment of the safety switch assembly 100 shown in fig1 the lift of the actuating bolt 22 of the locking mechanism 6 and thus the actuation of the locking lever 8 is executed in a same direction as the movement of the plunger 3 in order to enable a disengagement of the locking lever 8 and the cam disk 5 in case of emergency the locking mechanism 6 is further linked to a cam 16 which can be acted upon from outside only through application of a not commonly available special tool the operation of the safety switch assembly will now be described in more detail as applied to a protective screen surrounding the machine in the position shown in fig1 the key 2 is inserted in the keyhole of the housing 1 as the protective screen is closed and the motor m is in operation the insertion of the key 2 causes the plunger 3 to move upwards to thereby rotate the cam disk 5 via the pin 14 inside the oblong hole 15 at the same time the locking mechanism 6 causes the locking lever 8 via the actuating pin 22 to firmly engage with its hook 9 behind the lug 10 of the cam disk 5 so that the key 2 is secured to the housing 1 and is prevented from being extracted when the protective screen is to be opened to allow access to the machine parts for inspection or maintenance the electromagnetically actuatable locking mechanism 6 is energized to move the locking lever 8 via.