GB675539A - Control apparatus for electric heating units - Google Patents

Abstract

675,539. Electrically-tripped switches. PROCTOR ELECTRIC CO. March 15, 1950. [March 17, 1949] No. 6476/50. Class 38 (v). [Also in Group XXXV] A control switch for an electric oven, which allows (1) normal operation with the heating resistors 1a, 1b in series under the control of a thermostat 18, (2) flash heating with the resistors in parallel, followed by normal operation under thermostatic control, and (3) automatic de-energization of another heater 3 during flash operation, comprises spring contact arms 5-7 normally biassed to the right (as seen in Figs. 1a and 9) and co-operating with fixed contacts 9-13, the contact arms being connected by an insulating tie bar 8 and movable to the left (for flash operation) by a cam 16 operated by a control knob 29 which also actuates cams 17, 23 and 27. The tie bar 8, when sufficiently moved to the left, is retained in the flash position by a latch bar 14 engaging the edge of a bimetal latch 15 which then (over contacts 7, 13) shunts the contacts 21, 22 of the thermostat. When the thermostat contacts open the full current through resistor 1b also passes through the bimetal latch 15, which quickly heats up and releases the latch bar 14 so that the tie bar 8 and its associated contact arms spring to the right (cam 16 being so shaped as to allow this) to terminate flashing and establish normal operation. Cams 17 and 27 work on contacts 5 and 26 to isolate the resistors 1a, 1b from the mains L1, L2 when the knob 29 is in the "off" position. Cam 23 controls the setting of the thermostat.