If engine under heavy load has belt break or slip off this is to stop motor or engine if governor is slow or not working.
If electric motor it cuts off power circuit, if engine it cuts off battery power or opens ignition circuit
Tall rectangles are two wood stakes driven in ground beside flat power belt , chain drive, shaft linkage ( shown as 1 K ohm boxes) that will drop down if failure does occur.
The two center STSP below power belt is string or cord tied across both wood posts that is strong enough to hold two SPST switches ( these could be pieces of bent spring brass) on left wood stake closed.
In operation, should power break belt or slips off the belt should break one or both strings to quickly open circuit and shut down power system.
