GB714675A - Improvements in or relating to safety or protective cut-outs for electrical immersion heaters - Google Patents

Abstract

714,675. Thermal switches; switches partly electromagnetic. SARUM ELECTRIC, Ltd., and SPARROW, G. E. Dec. 11, 1951 [Sept. 11, 1950; Sept. 28, 1950], Nos. 22315/50 and 23773/50. Class 38(5) When the circuit of an immersion heater is broken at a predetermined temperature, it is maintained open by mains-energized means, such as an electromagnet, so long as the mains are energized. In one form of switch, Fig. 1, the contacts are in series with the heater 3 and are carried by adjustable resilient blades 21, 27, the blade 21 being actuated by a rubber diaphragm 12 connected to a capsule 9. Blade 21 forms a toggle with a lever 32 pivoted at 34 and carrying, or serving as, the armature of an electromagnet 37 which is connected across the mains. The arrangement is preferably such that the contacts open just as the toggle crosses its dead-centre position, the contacts then being held open by electromagnet 37 until it is de-energized. In a modification, Fig. 5, the lever 32 is replaced by a lever 38 which has a catch 39 which engages under blade 21 when the contacts open and retain it until a spring 40 pulls lever 38 to the right on de-energization of magnet 37<SP>1</SP>. To obtain a snap-action in this arrangement, the diaphragm may be of metal and is dished. The above switches are particularly suitable for A.C., and in a D.C. form, Fig. 3, the contacts 22, 28 are arranged to close on temperature increase to energize a relay coil 42 The relay armature 43 is thus moved clockwise and carries a contact stack down to open contacts 46<SP>1</SP>, 50, and 47<SP>1</SP>, 51, in series with the heater 3, and to close contacts 48<SP>1</SP>, 52 which short-circuit the contacts 22, 28, so that, as long as the mains remain energized, the heater is disconnected even after contacts 22, 28 reclose. The blade 21 may alternatively operate a mercury switch.