GB1429938A - Electric thermal overload relays - Google Patents

Abstract

1429938 Thermal overload relay MIDLAND ELECTRIC MFG CO Ltd 27 June 1973 [27 June 1972] 30058/72 Heading H1N A starting unit for an electric motor (Fig. 1, not shown) incorporates a thermal overload relay having independent heating elements 19 for three bimetallic heaters 20 which bend in the same direction on current increase and the relay includes coupling means to transmit this motion to an operating member 24 which actuates a snap-acting circuit-opening contact on a trifurcated switch contact blade 21. The coupling means, Fig. 3, comprises three separate elements 25, 26, 27 each with a portion 25a, 26a, 27a, the elements first being loosely assembled to a slider 28 by means of a screw 29 with the relay orientated so that the elements are vertical with the said portions uppermost and engaging their respective bimetallic strips under common temperature conditions before being rigidly secured together. An abutment screw 30 in the slider 28 acts between the coupling means and the operating member 24 for setting the operating current, a further adjustment facility being provided by movability of the pivot axis of the member 24 with respect to the contact blade 21 by means of an adjustment lever 25. The relay includes a generally cylindrical resetting element 31 movable rectilinearly and angularly about its longitudinal axis and having its inner end formed with a plane surface 31b and a cam surface 31c so that in the position shown in full in Fig. 2 it forms a stop to prevent the contact blade going over-centre and thus allowing the blade to reset automatically when the bimetallic elements cool. When turned through 180 degrees to the dotted line position the contact blade must be reset by depressing the element 31 to move the cam surface 31c against the blade.