Patent GB-444234-A (GB)
Title: Improvements in electric lighting installations
IPC: F21V25/06
Filed: 1935-07-04
Abstract: 444,234. Protective arrangements. COMPAGNIE FRANCAISE AUXILIAIRE DES MINES, 42, Rue du Polygone, Douai, Nord, France. July 4, 1935, No. 19133. Convention date, July 6, 1934. [Class 38 (iv)] In a protective system for a lighting installation as employed for instance to prevent sparking in mines in which the conductors, lamps and switches, are enclosed in casings containing fluid and in which the switches are opened whenever, due to leakage, the pressure falls below a minimum valve, the main switch and the auxiliary switches which carry the lamps are constructed as connection boxes with interchangeable lateral connections adapted to be connected in the line. The main switch is opened whenever a substantial drop of pressure occurs in any part of the system, but a local smaller drop of pressure in a lamp casing operates the corresponding switch to substitute for the filament an equivalent resistance. The connecting box enclosing the main supply switches is shown in Figs. 2 and 3, the casing 12 being air-tight and connected by interchangeable screwed joints to air-tight casings 96 which enclose the main leads 3, 7. The pin-and-socket connections 92, 93 at any joint are supported by insulating elements which are perforated to provide an air connection. The current is led from supply leads 54, 55 to the sockets 32, 33 and passes along leads 3, 7 to all the lamps in series. When one side of the box is blanked off by the closing cap 103, the return wire 42 is connected to the wire 41 and socket 33 through the pin-andsocket coupling associated with the closing cap. A connection to another pair of leads 3, 7 may replace the cap 103. The sockets 32 and 33 are connected respectively to the main supply wires 54, 55 when the pressure of air or other fluid in the casing is sufficient, through the pressure controlled switch shown in Figs. 4 and 5, this unit being mounted in the lower part of the casing 12. The supply wires 54, 55 are connected to the metal sectors 52, 53 mounted on the insulating block 46, the sockets 32, 33 being connected to the sectors 48, 49. The circuit is completed by bridging members 62, 63 carried by a cross-bar 66 mounted on a piston 69 when the piston is forced down into its cylinder by the internal pressure in the casing 12. When the pressure falls, the piston is forced up by a spring or other means and opens the circuit. The interior of the cylinder is connected to the atmosphere. A lamp unit which is adapted to substitute the equivalent resistance 140 for the filament of the lamp 1 when the pressure in the unit drops, is shown in Figs. 6 and 7, Fig. 10 being the wiring diagram. The main casing is connected by the interchangeable screwed joints to the tubular casings which enclose the main leads 3, 7 and has also attached thereto, by air-tight joints, the switching unit 167 and the glass casing 9 enclosing the lamp 1. The switching unit 167, shown in section in Fig. 8, includes a diaphragm 154 with centre contacts 156, 158 adapted to engage either the spring arm 162 connected to screw 147 or the spring arm 159 connected to lamp contact 161. The periphery of the diaphragm 154 is mounted on arms 153, 152 forming also an electrical connection to screw 146. The interior of the diaphragm chamber is connected to the pressure system above the diaphragm 152 while the exterior is connected to the interior of the glass casing 9. The pressure on the lower side of the diaphragm normally causes engagement of the centre contact 158 with arm 159, but when the. pressure in casing 9 is reduced due to any leakage, the centre contact 156 engages spring arm 162 and resistance 340 replaces the lamp filament. Referring to Fig. 10, in normal position main lead 3 is connected through wire 143, screw 146, diaphragm 154, contact arm 159, lamp contact 161, the filament, lamp contact 163, screw 145 and wire 142 to the main lead connected to the next lamp unit. When the pressure falls diaphragm 154 is connected to spring contact 162 whereby the filament is replaced by resistance 140.