Patent GB-1458738-A (GB)
Title: Line protectors for communications circuits
IPC: H04M1/74
Filed: 1974-08-21
Abstract: 1458738 Protective devices RELIABLE ELECTRIC CO 21 Aug 1974 [2 Jan 1974] 36688/74 Heading H2H A protective device for use in a communications system comprises an insulating housing, a base in which are mounted a number of plug type terminals, an arc gap assembly having two electrodes, a spring device biasing the arc gap assembly towards the base, means forming a conductive connection between one of the arc gap electrodes and one or more of the terminals, the means, the spring device and the arc gap assembly being placed in the housing coaxially in line with each other. A protective device comprises a housing 4 of insulating material closed at one end by a base 10 secured to the housing 4 by a screw 90. The base 10 is provided with a number of terminal pins, of which those referenced 14, 16 form the terminals of one communication line through one protector, those referenced 18, 20 the terminals of the other line through the other protector, 22 being an earthing pin and 24 a locating pin. The arc gap assembly has two carbon electrodes 62, 64 spaced apart by an insulator 68 to form a spark gap 66, the assembly being contained within an inverted cylindrical metal cup 58 over which fits a metal shunt 76 having fingers 78, a volute type spring 72 being contained between the cup 58 and the shunt 76. The shunt 76 is in contact with a metal plate 86 to which is secured the earthing pin 22. The protective device further includes a metallic bobbin 40 around which is wound a coil 50 having one end secured to the bobbin 40 and the other end attached to a metal band 48 around an insulating member 46 carried by the bobbin 40. The bobbin has a central bore 42 into which is secured by solder 56 a pin 52 which supports the carbon electrode 62. A metal spring like member 32 is secured to pin 16 and a cranked metal device 26 secured to pin 14. The device 26 makes contact with the bobbin 40 and arms 36 of member 32 are in contact with the metal band 48, thus a circuit exists between pins 14, 16 by way of elements 26, 40, 50, 48, 36, 32. In the second protector all the corresponding elements carry the suffix a. In operation should an excess voltage condition of short duration exist on a line connected to pins 14, 16 the arc gap 66 will break down and the excess voltage discharged to earth by way of the pin 22. Should an excess current condition exist in the line connected to pins 14, 16 the coil 50 will generate heat thereby melting the solder 56. The spring 72 then extends longitudinally to push the rim of the cup 58 into contact with the end flange of the bobbin 40 whereupon the line is again connected to earth as shown in the right hand section of Fig. 4. In the embodiment illustrated by Fig. 10 (not shown) the arc gap assembly is replaced by a gas filled assembly having opposed electrodes 98, 100 and an extra solder pellet 108. Operationally the embodiment is similar to that described above with the exception that either or both of the solder elements 56, 108 may melt and furthermore erosion of the electrodes 98, 100 may occur to allow movement of the cup 58. If overvoltage protection only is required the bobbin 40 and coil 50 may be omitted.