GB660887A - Improvements in snap-action electrical switches - Google Patents

Abstract

660,887. Retractive switches. IIYDE, N. E., HUTCHINGS, K. J., and BUCKINGHAM, J. Jan. 20, 1949. No. 1619/49. Class 38 (v). In a snap-action retractive switch intended primarily for cutting off the supply to electrical apparatus when a protective enclosure is opened, means are provided to ensure positive actuation of the switch contacts in the event of failure of a toggle spring. The switch comprises a link 8 pivoted at 9 to the switch casing, at 7 to an actuating push rod 3 and at 21 to a telescopic link 11 which is surrounded by a compression spring 12. The other end of the link 11 has a pin 19 engaging in slots 20 in one pair of limbs of a pair of L-shaped members 13, which pivot about in fixed pivots 14 and carry a contact roller 16. When a plunger 2 is depressed, the downward movement of the rod 3 causes the link 8 to turn clockwise so as to move the toggle mechanism over a dead-centre position and open contacts 16, 17 and close contacts 16, 18. In the event of failure of the spring 12, tension springs 23 move the pin 19 to the other ends of the slots 20 and cause slotted links 22 fixed at one end to the pin to move to a position where they engage the pivot 7 as well as the fixed pivot 14. This couples the rod 3 directly to the L-shaped members 13 and provides positive actuation. The provision of a bellows .5 surrounding the push rod 3 and return spring 4. enables the switch casing to be hermetically sealed, soldering lugs 24 being brought through the bottom of the casing by glass-tometal or ceramicto-metal seals. The casing may be filled with hydrogen, nitrogen or other inert gases or mixtures of inert gases. The removal of the sleeve 25 surrounding the bellows enables the plunger 2 to be replaced by another operating member such as a lever, without breaking the seal of the casing.