GB651883A - Improvements in thermally tripped electric switches - Google Patents

Abstract

651,883. Automatic circuit - breakers. SHARP, W. May 4, 1948, No. 12175. [Class 38(v)] A switch that opens automatically on the passage of excessive current comprises an insulating base 1 having a number of channels in each of which is a fixed contact 5 and a movable spring blade contact 3 which normally tends to separate from the fixed contact. Contact 3 is connected directly to a terminal 4, the contact 5 being connected to a terminal 10 through a heating wire 8 which is coiled round an insulating sleeve 9 surrounding a bi-metal strip 6. All the contacts 3 can be pressed into contact by a pivoted arm 11 carrying projection 13. When the arm is depressed, by a pushbutton 19, for example, it is held in the depressed position by a roller 14b on a swinging arm 14 which engages over an adjustable projection 16 on the arm 11. The arm 11 can be released, to allow the contacts to separate, by a second push-button 18 which when depressed bears against the arm 14 and swings it free of the projection 16. Excessive current through the switch also opens the contacts by heating the strips 6 and causing them to bend and move the arm 14 away from the projection 16. To prevent the switch from being closed before the strips 6 have returned to their normal positions a stop lever 21 is pivoted to the base and is connected by a spring 22 to the arm 14. When the arm 14 is moved by the bi-metal strips the lever 21 is brought into the path of a projection 23 on the arm 11 which cannot therefore be depressed.