GB711802A - Improvements in and relating to electric circuit breakers - Google Patents

Abstract

711,802. Automatic circuit-breakers. MECHANICAL PRODUCTS, Inc. May 28, 1951 [June 2, 1950], No. 12515/51. Class 38(5) A circuit-breaker which is trip-free for overload currents above a certain value but which can be held closed for overload currents beneath that value and which embodies certain features of the breaker disclosed in Specification 669,656, comprises a U-shaped bimetallic latch 34 connected by lateral extensions 32 to movable contactcarrying arms 30 and to a bimetallic ambient temperature compensating finger assembly 36, this assembly forming the subject of Specification 709,717. The breaker is normally held in the closed condition (Fig. 1) against the action of springs 52 connected to ears 34a on the latch 34 by the edge 34<SP>1</SP> of the latch 34 engaging ledges 50 on spaced blocks 44. The blocks 44 form part of a fixed structure 40 in which a switch operating plunger 42 is slidable, the plunger carrying a projection 48 in a slot 46 between the blocks. The end of the projection 48 lies substantially flush with the ledges 50 and co-operates with the edge of a depression 54 formed in the latch edge 34<SP>1</SP>, there being normally a small gap between the projection and depression. A T-shaped block 56 slidably mounted within the enlarged forked ends 58 of the plunger 42 overlies the inner ends of the arms 30 and has a recess 66 receiving a compression spring 55. On overload with the plunger 42 left free, the latch edge 34<SP>1</SP> leaves the ledges 50 and the breaker opens under the action of the springs 52, the latch 34 and finger assembly 36 sliding over opposite sides of the blocks 44 and being arrested by arms 30 engaging stops 57, the plunger 42 being outwardly projected by the spring 55. Depression of the plunger 42 for resetting first moves the plunger relatively to the unit 30, 32, 34, 36 until the gap between the projection 48 and edge of the depression 54 is taken up, whereupon the projection 48 moves the unit and the latch 34 springs back on to the ledges 50. Owing to the taking up of the aforementioned gap the T-shaped block part 60 is clear of the arms 30 and thus the latch is free from influence by the spring 55 during resetting. On overloads up to certain value, if the plunger is held depressed, the latch 34 leaves the ledges 50 but is immediately arrested by the depression 54 engaging the projection 48 and the contacts 22 remain closed. On overloads above that value the latch depression 54 moves clear of the projection 48 and holding the plunger 42 cannot maintain the breaker closed. On subsequent release of the plunger the projection 48 is moved by the spring 55 beneath the latch 34 by flexing the latter and is thus repositioned opposite the depression 54 in readiness for re-closing the breaker. The breaker may be manually opened by pulling the plunger 42 so that the enlarged end 58 deflects the latch 34 to disengage the ledges 50.