(57) A snap-acting bimetal blade for use as a thermally-responsive switch actuator has
a generally rectangular outer shape and has a generally rhomboidal cut-out defining
two spaced-apart and tapering legs connected together at their opposite ends. Such
a blade shape has advantageous characteristics as regards the forces and movement
that can be developed in switching operations. A thermally-responsive switch incorporating
such a bimetal blade has first and second spaced-apart metal parts, one of which is
formed of rigid, electrically-resistive material and the other of which is a spring
member, first and second contacts provided on such parts, a bimetal blade as aforesaid
welded to one of the parts, and an insulating push rod arranged for transferring switch-operating
movement of the bimetal to the spring member for operating the switch. When used as
a motor protection switch, the bimetal operation is dependent upon heat generated
by current flow in the electrically-resistive part of the switch and the switch can
be made relatively insensitive to large currents flowing for short durations, but
sensitive to longer term lower currents, and can have a high ratio of "off" time
to "on" time.
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