Overload box housing the thermal overload device for motor starting switches

摘要

696,299. Thermal switches; electrically-released switches. CRABTREE & CO., Ltd., J. A. Sept. 27, 1951 [Nov. 17, 1950], No. 28117/50. Class 38(v) The overload release devices of a polyphase contactor switch substantially as disclosed in Specification 633,393 comprise a part-cylindrical bimetal k having an extended leg kSP1/SP engaging a trip bar l and surrounding a heater r, the other end of the bimetal being riveted at kSP2/SP to an L-shaped bracket n. The bracket n is apertured to receive a boss o on the base of the insulating overload box dwhereby adjustment of the leg kSP1/SP in relation to the trip bar l may be performed by rotating the bracket n on the boss o and clamping it by a screw q passing through an arcuate slot p in the box base and engaging a tapped hole in the bracket n. The trip mechanism i operated by the bar l and "stop" button 18 is as disclosed in Specification 674,084. The heater r may comprise a coil brazed at one end rSP1/SP to a connector strip sSP2/SP and at its lower end to a stem s, the upper end of a stem s being bent forwardly to form a connector strip sSP1/SP and the lower end being received in a recess oSP1/SP in the boss o. The strips sSP1/SP, sSP2/SP, are riveted at tSP1/SP to an insulating plate t which covers a circular opening dSP2/SP in the box cover dSP1/SP, and their forward ends are downturned and bifurcated at sSP3/SP and secured by terminal screws u. To change a heater r the screws u are loosened and the plate t and heater are removable as a unit. A strap w connects one terminal u of each pair to a main terminal x, and a strap y the other terminal u to a main contactor switch contact eSP1/SP. For small currents the heater r is composed of fine wire wound on a tubular ceramic former located on the stem s. For heavy currents the heater comprises a partcylindrical strip Figs. 6, 7 (not shown). The "start" mechanism j housed in an end compartment g in the box d comprises four vertical hexagonal pillars 8 having contacts 8SP1/SP pairs of which are respectively engaged by contact blades 9, 9a, freely mounted on a bar 11 operable by a "start" button 12. The bar 11 also extends through arms of a cradle 13 slidable on the base of the box d and extends freely through a fixed plate 14. A washer 15 is secured to the bar 11 so that a compression spring 16 abutting the plate 14 and the contact blade 9 urges the parts to the "off" position, Fig. 3. Pressing the button 12 moves the blades 9, 9a, with a rolling motion to the chainline position in which the contactor operating coil circuit is completed so that the contactor closes, another circuit, e.g., the coil circuit of another contactor, being broken. An arm 11a on the bar 11 is engaged by a part movable with the contactor armature to hold the contacts 9, 9a, closed, Fig. 1 (not shown).