BEMF unit ensures that motor-driven equipment up to 600 V, with variable rundown time (mixers and mills), has completely stopped before access is possible. While electric motor rotates, monitor gauges electromotive force. When EMF reaches zero and motor has come to complete standstill, monitor releases trapped key corresponding to lock on machine guard's hatch. Unit connects to ac/dc motors, as well as motors with dc braking systems and VS drives.