GB739143A - Improvements in thermo-electric switches - Google Patents

Abstract

739,143. Automatic circuit-breakers. GENERAL MOTORS CORPORATION. Nov. 10, 1953 [Nov. 13, 1952], No. 31056/53. Class 38 (5). An adjustable thermal overload switch comprises a switch rod 12 carrying contact 15 which bridges contacts 19, 20 on switch casing 10 and engages between knife edges 24, 25 of a spring-biased pivoted arm 23, the position of the pivot 26 of which is adjustable with respect to the end 44 of a series bimetal element 31 engaging its end 47. When overload occurs, the element 31 disengages from arm 23 allowing the arm to spring back and move rod 12 to the open position shown in Fig. 2. Two mounting plates 32, 30 for pivot 26 are provided having a common pivot 33 in the switch casing 10, the former being screwed by screw 35 to the casing 10 and the latter being secured by screw 38 to plate 32. The pivot pin 26 is journalled in a hole 27 in plate 30, and when a different current rating for the switch is required, the plate 30 is replaced by one having the hole 27 in a different position to vary the amount of overlap of end 47 with the end 44 of the bimetal strip. For higher current ratings of the switch, the element 31 may be shunted by a resistance 60. After operation, the switch is manually reset. The switch is used (Fig. 1) as an overload switch for a motor 50 having a starting winding 52 disconnectible by a centrifugal switch 53, and a running winding 51.