Double switch fuse assembly

Claim 1

In an automatic control system for a heating plant having a burner, first motor means for supplying fuel to said burner, and a heating stack for discharging the products of combustion, said heating stack containing a damper vane moveable between a closed position wherein said stack is closed to flow and an open position wherein said stack is open to flow, the improvement comprising means for mechanically biasing said damper vane into its open position, second motor means upon energization for overcoming said biasing means and moving and maintaining said damper vane into and in its closed position, voltage source means for energizing said motor means, a normally closed first switch and said second motor means forming a first series circuit connected to said voltage source means thereby normally maintaining said damper vane in its closed position, a normally open second switch, solenoid means in response to closing of said second switch for opening said first switch thereby causing deenergization of said second motor means and movement of said damper vane by its biasing means into its open position, a third switch mechanically linked to said damper vane to be closed only when said damper vane is substantially fully in its open position, said third switch and said second switch being in series with each other and forming part of a second series circuit connected to said voltage source means, both of said series circuits being in parallel with each other, means in response to closing of said second switch and movement of said damper vane from its closed position into its open position for causing closing of said third switch for energizing said first motor means, and fuse means destructing in response to closing of said second switch at a time when said third switch is short circuited through for at least partially disabling said control system.