How is this requirement (“difficult to defeat”) being addressed by safety interlock switch manufacturers?
• What are “positive-break” safety interlocks “Positive-break” safety interlocks are electromechanical switches designed with normally-closed (NC) electrical contacts which, upon switch actuation, are forced to open by a non-resilient mechanical drive mechanism. (Spring actuators are not considered positive-break mechanisms.) The actuator key is typically mounted to a movable guard – such as an access door, protective grating, equipment hood, or plexiglass safety cover. When the guard is closed, the actuator mates with the electromechanical switching mechanism. Upon opening of the movable guard, the actuator key mechanically rotates a cam mechanism – forcing the NC electrical contacts to open the safety circuit. For machine applications with residual motion after shut-down, key actuated interlocks are available with a solenoid latch – which, in conjunction with a time-delay, motion detector, position sensor or other machinery status monitor, can delay access to hazardous areas until sa
