A window operator has a prime mover for opening and closing of a window, with the prime mover being drivingly connected to a drive output member through an intermediate gear structure. A clutch device in the drive structure senses the torque applied to the drive output member in a window closing operation and a switch operable by the clutch is effective to deenergize the prime mover when the torque applied to the output member reaches a predetermined value. The switch can be adjustably located relative to the clutch whereby the predetermined value at which the motor will be deenergized may be varied in order to obtain a desired tension on a member connected to the closed sash of the window, such as a chain connected to the sash of a skylight window.