GB560264A - Improvements in contact arrangements of electric switches - Google Patents

Abstract

560,264. Thermal switches. BRITISH THOMSON-HOUSTON CO., Ltd. Oct. 29, 1942, No. 15208. Convention date, Oct. 31, 1941. [Class 38 (v)] A thermally-operated element acts on a pivoted contact base 31 to open a circuit. One fixed contact 24 is attached to a part of the casing but is preferably mounted on a flat bent strip spring, while the other 34 is carried on a spring blade 33 fixed to the base 31 and extending down behind a rigid magnetisable arm 35 secured at its upper end to the blade 33 near its connection with the base 31. The contact 34 is borne on a pin 34a which passes through the arm 35. A permanent magnet 28 is mounted so as to hold the contacts in engaged 'position. Successive positions taken up by the contact arm in opening and closing the circuit are shown at a ... e in the Figure. The pivoted base 31 is caused to rotate anticlockwise under the pressure of a thermostatically operated arm on the projection shown. The contacts remain held together by magnetic force while the spring bends at 37 until at a given point they snap apart, the spring straightening (position c). On release of' the thermostatic pressure the magnetic attraction on the armature 35 causes rotation of the base 31 in a clockwise direction, say from position c to position d, when the attraction overcomes the spring 37 to bring the contacts together (position e). During these operations, the movement of the contact 34 is first a sliding one downward (position b), which will break any weld on the contacts. On re-making the circuit, a weld may occur which will hold through continued movement clockwise of the base 31 until position a is reached. If no weld happens there will be a slight upward sliding movement from position e. Provision is made for the contacts to be held apart in one position of the knob adjusting the thermal device (not shown). Specifications 423,897, 424,746, [both in Group II], and 451,832 are referred to.