Patent GB-486796-A (GB)
Title: Improvements in and relating to electric switches
IPC: H01H35/10
Filed: 1936-12-16
Abstract: 486,796. Electric switches ; electric motor control systems. BRITISH THOMSON-HOUSTON CO., Ltd. Dec. 16, 1936, No. 34624. Convention date, Dec. 17, 1935. [Classes 3S (iii) and 38 (v)] [Also in Group XXXV] An electric switch, particularly for selectively connecting windings of a motor in series or in parallel, comprises a number of fixed contacts 25-28, Fig. 5, and a switch member 33, 34 for connecting together contacts 25, 26 and 27, 28, respectively, when a plate 32, Fig. 1, carrying the parts 33, 34 is rotated to such a position as to be moved inwards by a biassing spring 35, means being provided for restraining the plate 32 against rotation when in the closed circuit position, and there being provided also means responsive to a predetermined flow of current through the switch for moving the plate 32 outwards against the spring 35 to open-circuit position. The switch may be used for connecting motor windings 18, 19, in series or in parallel according to the supply voltage. The plate 32 carrying the contact plates 33, 34 is carried by a rod 31 which is provided with an arm 36 having a projection 37. Two apertures arc provided in a cover 30 attached to the motor casing 14 such that when the projection is brought opposite to one of the holes and the rod 31 and plate 32 are allowed to move inwards under the force of the spring 35, the plates 33, 34, connect the contacts 25-28 and therefore the windings 18, 19 in parallel as shown in Fig. 5, but upon pulling the rod 31 outwards to disengage the projection 37 from the aperture and rotating it so as to bring the projection opposite the second aperture, the rod and plate can move inwards to connect together contacts 26, 27 and leave contacts 25, 28 disconnected whereby the windings are connected in series. A heater coil 29 is provided in series with the motor windings such that on the occurrence of an overload the switch plate 32 is moved outwardly to open circuit position. The coil 29 surrounds a sleeve 45, Fig. 4, united to a stationary shaft by solder and carrying a ratchet wheel 44. A pivoted lever 39 pulled upwards by a spring 41 is normally restrained from movement by a latch 43 engaging the wheel 44 ; upon the occurrence of an overload, the solder melts, and frees the ratchet 44 so that the lever 39 moves upwards and presses the rod 31 and plate 32 outwards against the force of the spring 35 to the open-circuit position. When the solder solidifies, the switch can be reset by pressing in the rod 31. A centrifugal device 22 is also provided having a movable contact 50, and a fixed contact 48 which are held in engagement while the motor is starting up or running at slow speed to connect a starter winding 20 and a condenser 21, in the motor field. The movable contact 50 is carried by a resilient bifurcated member 52 biassed by spring fingers 54 to the open position but held in contact with the fixed contact 48 when the motor is at rest by a slidable collar 56. This is moved outwardly by springs 58 which bias operating toggles 59, 60 to the locked position. This bias is overcome when the speed of the motor is sufficient by the centrifugal force exerted by the weighted links 60 of the toggles which move outwardly and thus move the collar to the right and permit the spring 58 to move the contact 50 out of engagement with the contact 48.