Patent GB-392925-A (GB)
Title: A method of and apparatus for electrically illuminating coal mines and other localities
IPC: F21V25/12
Filed: 1931-11-13
Abstract: 392,925. Electric supply systems. REYROLLE & CO., Ltd., A., Hebburn-on- Tyne, and RUSSELL, R. M., Wester Daldowie House, Broomhouse, Lanarkshire. Nov. 13, 1931, Nos. 31447/31 and 35131/32. [Class 38 (iv).] Installation wiring arrangements: switching systems.-In an electric lighting-installation, specially suitable for use in mines, a polyphase main circuit A supplies through a transformer A<1> a polyphase low-voltage circuit in which lighting equipment units, each comprising a cable section and group of lamps, are supplied in series and the individual lamps G in each such group are so connected that normally the load is substantially balanced on the several phases. In the arrangement shown in Fig. 1, each such lighting equipment unit comprises a section of a four-core cable with three insulated phase conductors F, each supplying one of the three lamps G, and an insulated neutral conductor F<1>, one end of the cable section terminating in a plug member E<1> of a flameproof connector and the other end in a socket member E of a similar connector, and a metal cap E<2> is provided to cover the socket member E of the last unit. The neutral conductor F<1> is connected to the metal casings of the lamps and connectors. In a modification a five-core cable is employed, the additional conductor being an insulated pilot wire' running the whole length of the lighting circuit with connection through an additional plug and socket in each pair of connectors E, El, the cap E<2> carrying a plug for connecting the wire to its earthed casing. The connectors E, E<1> are so arranged' that in separating them the pilot wire connection is broken before the connections for the conductors F and in coupling them together the pilot wire connection is made last. Between the transformer A<1> and the first socket member E each phase is provided with a contactor switch B, an electromagnetic or thermal overload device C and a pushbutton control switch D. Closure of a switch D energizes the coil B<1> of the associated switch B which closes a holding circuit through contacts B<2> enabling the switch D to be released. The circuit remains closed until opened by the associated overload device C or by opening normally closed pushbutton contacts D<1>. Figs. 3 and 4 show a suitable construction of lamp G and its mounting on the cable. The lamp is screwed into a carrier L carried by a spring L<1> seated on the cover H<2> of a casing H provided at each end with a cable grip H<1> or, in the case of the end lamp in a lighting equipment unit, with a socket member E in place of one such cable grip. Insulating blocks J within the casing H are clamped by a bolt K<1> between a metal block K and the cover H<2> and are provided with metal insets J<1> bored at J<2> and provided with clamping screw J<3> to engage the bared ends of the phase conductors not supplying the lamp and of the pilot wire if such is used. The bared end of the phase conductor supplying the lamp is similarly engaged by a clamping screw K<3> in a bore in the block K and the neutral conductor is connected to an earthing screw H<3> or to the wall of the casing H through one of the bores J2. The current passes to the lamp through the bolt K<1>, insulated from the cover H<2>, and through a spring-pressed plunger M, the spring L<1> providing the return connection to the earthed casing H. The lamp is enclosed in a globe N carried by a holder O which screws on to the cover H<2> to clamp the flange N<2> of the globe against a ring N<3>, with the interposition of asbestos or like packing rings N<1>. The holder O carries a protective cage N<4> and its underside is provided with four inclined recesses O<1> for engagement with a spring- pressed iron detent P mounted in the wall of the casing H, so that the holder O can readily be screwed into position but can be unscrewed only after withdrawal of the detent by a magnet inserted in a recess P<2>. To prevent glare and the casting of sharp shadows of the cage N4, the globe N is shaped in cross section as shown in Fig 5. Fig. 6 shows a modified construction in which the lamp G is screwed into a carrier L slidable against a spring L<2> in a cylinder Q secured to the clamping ring N<3>, a stronger spring R being arranged between the top of the lamp G and the globe N so that it normally presses the lamp terminal G<2> against the end K of the bolt K<1>. A stop Ql on the cylinder Q limits the travel of the carrier L and in the event of fracture of the lamp the spring L<2> acts to break the circuit within the flameproof compartment of the cylinder Q, whereupon a spring-pressed plunger Q<2> engages beneath the edge of the carrier L to prevent reclosing of the circuit.