Patent GB-190505073-A (GB)
Title: Improvements in or connected with Means for Automatically Breaking an Electric Circuit in the Event of a Leakage to Earth.
Filed: 1905-03-10
Granted: 1906-01-11
Abstract: 5073. Nalder Bros. & Thompson, and Harris, A. F. March 10, Cut-outs; switches.-In order to break a circuit automatically in the event of a leakage to earth, two wires, through which current passes from the respective supply terminals to the leads, are wound in opposition, so as to produce no magnetizing effect, on the core of an electro-magnet, the armatare of which thus remains unattracted while normal current is flowing. If either of the leads becomes earthed, the armature is attracted and operates a circuitbreaker, preferably by means of a relay. It may also give an alarm. Pref e r a b l y, the circuitbreaker is constructed so that it cannot be re-set until the fault is remedied. In the form shown in Fig. 1 and diagrammatically in Fig. 4, the normal path of the current is from the supply wire c along a conducting- arm g, pivoted at g<1>, to a fixed contact g<2>, through one winding b<2> of the differential magnet b, and out by the post c<x>, to the lamps, motors, or other current-consumers, returning by the post c<x2> through the second magnet winding b<1>, a fixed contact f<2>, and switch lever f, pivoted at f<1>, to the return wire c. Alightly-mounted armature b<3>, when attracted by the magnet b, carries a spring b<x> against a fixed contact c<x>, thereby closing a sbunt circuit containing the relay magnet e, which then attracts its armature e', and unlatches the switch barf, which is then pulled off by a spring f<3>. An alarm x may be sounded at the same time. The re-setting device consists of a link f<4> pivoted at one end to the bar f and having at the other end a slot f<5> enclosing a pin g<3> on the lower end of the bar g, so that this bar is unaffected by the throwing off of the lever f. On movement to the right of the handle g<4>, which projects outside a box containing the rest of the apparatus, the bar g is first separated from the contact g' and then the lever f<4> is re-set, but, if the fault remains, it is thrown off again, either at once or after the bar g has been brought back against its contact g<2>, thus showing on which side the fault occurs. In an alternative arrangement, both switch bars are placed in series in one or other of the mains. The coupling-bar may be replaced by the mechanical construction serving the same purpose shown in Fig. 5, in which the bar g is also adapted to act as a quick-break hand-switch. In another modification, both sources of supply are cut off simultaneously, when the bar f is released, by having coupled to it by an insulated link a similarlymounted bar which makes the additional break, and both bars are re-set as in the simpler form. Pairs of contacts may replace, in each case, the single contacts g<2>, f<2>, the bars then acting as bridging-pieces. The mechanical construction is varied still further in another form, shown in Figs. 8, 9, and 13. One pair of contacts f<2>, f<2x> between the posts c<1>, c<x1> and a second pair f<2x><1>, f<2x2> between the posts c', c<x2> are normally bridged by brushes f <x> <x>, f <x> <1> carried by a pivoted frame f which is latched in position by the relay armature e' against the pull of springs f <x2>. When the compound electro-magnet b draws the contacts b<x>, c<x> together, completing the circuit of the relay e, the frame f rises and interrupts both sides of the line. For re-setting, a handle i is provided on the end of a push-bar i<1>, which, when depressed, carries a bridging-piece g away from two brushes g<2>, g<2x> x against which it normally rests, thus, as in the other modifications, temporarily cutting off one source of supply while reconnecting the other. The piece g is in the form of a collar capable of sliding on a fixed rod g<1>, and, when released, is returned by a coiled spring g<8>.