Our Electronic Timed-delay Unit Trapped Key Interlock Switches are used in applications that require an elapsed time to occur before allowing access to a hazardous area. This interlock switch uses a CU1 control unit timer to execute the timing sequence. Turning a non-removable key initiates the timer. When the CU1 times out, its output energizes an internal solenoid, which then allows the removal of either one or two trapped keys.