Patent GB-661282-A (GB)
Title: Improved electric circuit overload protective device
IPC: H01H71/58
Filed: 1948-10-12
Abstract: 661,282. Automatic circuit breakers. GENERAL MOTORS CORPORATION, Oct. 12, 948. No. 26518/48. Class 38 (v). A switch, particularly for overload protection, which is trip free and cannot be manually opened, comprises Fig. 1, a slide 42 locked against a spring 46 by a pawl 44 engaging a ratchet 26 which is held bv solder heated by a series coil 24. In this position the spring blade contacts 32, 36 are closed and the load 22 energised, and the manual reset bar 48, having an indicator extension 50, is held against its spring 56 by a pin 58 engaging a projection 60 on the slide 42. On overload the pawl 44 is released and the slide 42 moves the contact 32 to open the circuit and is arrested by a stop 62, this action taking place even if the reset bar 48 is held. During this movement a latch 64, pivoted on the slide 42 and normally held retracted by a spring 66, engages a pin 68 whereby it is rotated counterclockwise to engage a notch 70 in the reset bar 48, Fig. 3. Whilst moving the reset bar 48 to reclose the switch, the contacts 32, 36 are held open by the latch arm 72 which flexes the blade 36 and the circuit is not remade until the pawl 44 is held by the ratchet 26 and the latch retracted bv the spring 6.6; hence subsequent movement of the reset bar 48 cannot affect the switch. Fig. 5, an insulating case 120 has vertical slideways 122 in opposite walls which support, back-to-back, a flanged push button slide 124, and a flanged pawl slide 126, A contact-breaker 128 carrying contacts 146. has notches 130, Fig. 12, loosely engaging edges 132 of an aperture in the pawl slide 126 and is pressed against a rounded projection 134 thereof, whereby it is pivotally attached thereto, by a spring 136 located bv a tongue 138 on the contact-breaker 128 and a peg 140 on the casing. Normally, a pawl 166 on the slide 126 engages a ratchet 160 held by solder, and the spring 136 biasses the contacts 146 into engagement with fixed contacts 150, 152 mounted on a removable back plate 154. The solder is heated by a strip 162 connected between a terminal 164 and the contact 152. On overload the slide 126 is raised by the spring 136, and eventually shoulders 142<SP>1</SP> on the contactbreaker 128 are arrested by stop blocks 168, 170 in the top of the casing 120, whereby the contact-breaker 128 is pivoted counterclockwise and the contacts 146, 150, 152 are opened. This action is accelerated by depending ears 142 on the contact-breaker 128 being engaged by projections 144 on the slide 126, Fig. 7. The slide 124 is urged upwardly by a spring 194 seated in a well 196 in the casing 120 and bearing against an ear 198 which in turn engages a projection 144 on the slide 126. Upward movement of the slide 124 on tripping is limited by a projection 121 on the pushbutton 184 attached thereto. Resetting by depressing the button 184 causes a projection 125 thereon to engage an extension 127 of the contactbreaker 128 whereby the contacts 146 are held open while the slide 126 is moved down by the engagement of the ears 142 with the projections 144, the contacts 146 being closed after engagement of the ratchet 160 by the pawl 166, by release of the push-button 184. In the closed position the extension 127 is aligned with a recess 129 in the button 184 so that holding of the latter cannot prevent the switch tripping open nor can depression thereof affect the switch parts. The button 184 is plastic and coloured white and has a separate red cylindrical part 186 which is first slid over the initially parallel-sided flexible prongs 188, 190 of the slide 124. The button 184 is then inserted and the projection 192 spreads the prongs 188, 190 which thereby secure the part 186 and dig into the stem 192 to prevent removal of the button 184.