GB972273A - Improvements in or relating to electric protective devices - Google Patents

Abstract

972,273. Electrically-tripped switches. J. CRAWFORD. Jan. 13, 1961 [Oct. 14, 1959], No. 34738/59. Headings H2B and H2K. An electromagnetically-tripped switch comprises fixed contacts 5 co-operable with a spring bow 6 biased by compression springs 10 and carried by an arm 8 pivoted at 9 and biased by a tension spring 12. The contacts are closed by rotation of a handle whose arm 17 engages the arm 8 which is held in the closed position by a latch 25 formed from an arm 18 pivoted at 20 and biased anti-clockwise by a spring 21. To open, the arm 16 is raised thereby depressing the arm 18 by means of a link 26 and allowing the spring 12 to rotate the arm 8, the stress in springs 10 determining the time lapse between the disengagement of members 8, 25 and the separation of the contacts 5, 6. These contacts are in series with a solenoid coil 30 whose armature 41 engages a slot 43 in the arm 18, so that upon the occurrence of a low overload, movement of armature 41 trips the switch. The coil 30 is in series with a fuse 35 mounted on a carrier 36 and engaging clips 34 in a recess 40 of the switch casing 1, a heavy overload causing blowing of the fuse 35 and tripping of the switch. The coil 30 may be in parallel with a bi-metallic element which opens the parallel circuit on low sustained overload to produce electromagnetic tripping of the switch. The link 26 may be arranged so that electromagnetic tripping moves the handle to the " OFF " position. The contacts 5 may be mounted on compression springs, additionally or alternatively to the bow 6 which may be laminated. A three-phase A.C. circuit may be controlled by three of the above switches or a D.C. circuit by two switches, only one of which is in series with a solenoid and a fuse. The terminals 27, 38 may be replaced by contact plugs.