the place i work is putting prox switches in for safety switches. when the guard cover closes the prox allows the machine to start. also when the gurad is opened during opperation the machine stops. they work o k but are easily defeatable. i was under the impression that a positive contact switch needed to be used. somthing with a key like device that fits into the switch body. am i wrong? the machines we are talking about are printing presses on a paper bag line. we make paper bags. my boss(a mechanical engineer) feels these are o k. i think we need to use somthing different. can anyone quote the passage in the standards about safety switches on machinery?