Abstract: A safety switch assembly as part of a protective screen by which a motor-driven machine is enclosed includes a locking unit for allowing opening of the protective screen for access to the machine only after all moving motor parts are at a standstill, and a plunger which actuates an electric switch for cutting the electric supply to the machine. The plunger is linked to a control member which is moved by the plunger in response to a key insertable into a housing by which the safety switch assembly is fully enclosed. The locking unit includes a locking lever which is actuated by an electromagnetically actuatable locking mechanism to engage and immobilize the control member with the electric switch being actuated by the control member.