Abstract: A five pin protector module for telephone circuits comprises two input pins, two output pins and a grounding pin, all on an insulative base. The electrical current path between each input pin and its respective output pin comprises an electrically conductive arm, a current responsive assembly and an electrically conductive helical spring. The module contains a bidirectional voltage sensitive switch which prevents input voltage surges from reaching the output but, instead, conducts them to a grounding member to which the grounding pin is attached.

Abstract: An individual subscriber circuit protector module employing solid state circuitry for protection against momentary voltage surges, and having firmly sensitive heat coil assemblies for protecting against continuous excess current surges. Fail-safe protection is also provided which becomes operative in the event of failure of the heat coil protection.

Abstract: A combined transient voltage and sneak current protector is presented. The protector device comprises a two-piece substantially rectangular insulative housing. The housing has four spaced and aligned openings at the bottom thereof for receiving upstanding terminals from a terminal block. The interior of the housing is loaded with four contact members which are adapted to effect electrical connection with a three element surge suppressor (e.g. transistor) and a pair of small cylindrical fuse elements. Each of the four contact members include a female connector communicating with the four aligned openings in the housing. The housing interior also includes a ground contact which electrically connects to the middle element on the surge suppressor. The ground contact passes through a lateral opening in the housing for mating with a novel plug-on grounding bus connector.

Abstract: A lightning protector assembly for telephone circuitry and the like includes a housing formed of a lower necked terminal section and an upper expanded grounding section. A component-mounting member is disposed within the housing for mounting a first pair of voltage limiting devices and a first pair of impedance devices. There are cavities provided in the lower part of the component-mounting member for receipt of a plurality of terminal contacts. The upper section has a pair of top recesses separated by a central bridging portion. Plug-in fuse holder units are disposed within the top recesses. A side ground contact is provided and includes an elongated horizontal member extending inside and across the width of the housing for connection to the first pair of voltage limiting means and a portion thereof extending externally of the housing.

Abstract: A gas filled surge arestor has at least one external air back-up gap comprising two spaced electrodes(7a,2 or 7a,3), one (7a) of which has at least one sharp edge or corner (9) adjacent the other electrode (2 or 3). The said one electrode (7a) is resiliently urged towards the other electrode and is coated with an insulating material (8) which prevents the two electrodes from being in direct contact and hence short circuiting. The arrangement is such that, although the sharp edge or corner (9) on said one electrode has a covering of insulating material, it is also separated from the other electrode by an air gap.

Abstract: A fail-safe secondary fuse device for assuring the grounding of a conductive gas tube used in modular protection devices for individual subscriber circuit pairs. The device resiliently engages each of the three end and center electrodes normally provided on the tube. In the case of the end electrodes, the device is insulated from direct electrical communication by a fusible sleeve of insulative material which fuses under heat emanating from the gas tube with the occurrence of continued current overload.

Abstract: A line protector module device for a communications circuit having a line protector circuit assembly including a base, a frame having a retaining portion, a spring mounted to the base, an arrester and a solder pellet compressibly held between the spring and the retaining portion of the frame. The spring is constructed of a strip of material which is formed in an S-shape. The spring has tabs formed in the material so that when the spring is subjected to a predetermined amount of compressive force, the tabs prevent nonrecoverable compression.

Abstract: A thermal protection device for overvoltage suppressor which includes spaced contacts 6 mounted in overvoltage suppressor magazines 11 of communication systems. A bow-type spring 3 and a melt element 2 l are arranged with the overvoltage suppressor which is mounted in a chamber of a case body or housing 13. The melt element is pierced by at least one arm of the bow-type spring when an overvoltage occurs for short-circuiting the two contacts of the overvoltage suppressor. A thermal protection device with simple components prevents creepage currents between the bow-type spring and the contacts of the overvoltage suppressor 6, a chamber for the overvoltage suppressor is adjacent and abutting to a separate chamber formed in the case body for accommodating a bow-type spring. Between the two chambers there is a separating wall comprising a thermoplastic melt element.

Abstract: A central office protector module which includes a light to provide a visual indication whenever the module shorts either of the lines protected by the module to groud as a result of either a sustained overcurrent or overvoltage condition on either line. The module includes a sixth or alarm pin in addition to the two line pins, two equipment pins and one ground pin usually included in the module. The module also includes two internal alarm terminals which are each associated with a respective one of the lines. The light is connected to those terminals and a source of voltage. The alarm terminals are connected to ground to complete the circuit to the light when the associated line is connected to ground within the module.

Abstract: A transient suppressor device assembly having at least two electrical components and a fail-safe clip. The fail-safe clip has means for simultaneously providing the necessary electrical conductive paths, providing fail-safe operation if an electrical component becomes overheated and holding together the electrical components.

Abstract: The lightning arrester device comprises an external metal casing (1) defining an enclosure (2) containing a neutral gas, and at least one metal rod (3a, 3b) forming an electrode and penetrating into the interior of the casing, insulating sealing means (4) being provided between the rod and the casing in order to close said casing, and comprising, moreover, at least one fusible element (5) adapted to create a short circuit between the electrode (3a, 3b) and the casing (1) when the quantity of energy to be diverted by the lightning arrester device exceeds a specified threshold.

Abstract: A self-contained air gap spark arrester assembly is disclosed which may be constructed and tested prior to its incorporation into a fail-safe surge arrester assembly. The air gap spark arrester assembly comprises a rivet shaped electrode, on which are concentrically mounted an insulating ring, a ring electrode, and an insulating spacer ring. These elements are arranged so as to provide an air gap between the two electrodes, aproximately equal to the thickness of the spacer ring and shielded from particulate contamination. Due to the placement of the assembly's electrodes, it is particularly well suited for combination with gas tube arresters in metal canisters. In one embodiment the canister is of cylindrical form and houses a fusible alloy spacer, a cylindrical gas discharge tube, and the air gap spark arrester assembly.

Abstract: A system for providing power to a central office protector module which has a visual indicator for indicating an alarm whenever one of the two lines protected by the module is shorted to ground by the module. The system includes at least one connector block which has a group of receptacles for receiving the module. The system includes a power supply which converts central office battery to a relatively low amplitude voltage to provide power to the alarm indicator. Current flows only when the module shorts the line to ground. The power supply also includes its own alarm indicator and also has provision to test that indicator and provide a remote alarm.

Abstract: Disclosed herein is a short-circuit device of a gas-filled triple-pole discharge-tube type arrester used for telephone lines, wherein a coil-like resilient short-circuit lead is arranged between the lead of an earth electrode and the leads of two line electrodes in an entwined condition through coatings of low temperature-meltable insulator.

Abstract: When the lightning device is overheated because of its long-time discharge, a conductive member having a low melting point is softened and melted by the overheated tube to short-circuit an air gap between main discharge electrodes. The main discharge electrodes are thus short-circuited to protect the lightning arrester from being overheated and damaged. When discharge function is lost between the main discharge electrodes, air discharge is carried out in the air gap. Electric appliances and machine connected to the lightning arrester can be thus protected from high voltage surge.

Abstract: A safety device for telecommunication equipment wherein a telecommunication circuit is promptly grounded when overvoltage is applied to the circuit or overcurrent is led to it and in which the production of excessive head and of damage to the communication equipment is prevented.

Abstract: An impulse rocket propellant is comprised of highly hydrated minearl salts such as boric acid hydrate HBO.sub.2.H.sub.2 O and a plaster forming agent comprising calcium oxide hydrate CaO.H.sub.2 O and sodium sulfate hydrate Na.sub.2 SO.sub.4.10H.sub.2 O, all of which are compounded and intimately commingled with a heat conducting inorganic fiber such as glass wool. When these compounds are allowed to dry, loaded into suitable rocket devices, and instantaneously heated, the water of hydration of the hydrated mineral instantaneously vaporizes into steam which can be used to propel the rocket. The resulting unhydrated mineral salts are entrained within the steam. Upon coming into contact with the atmosphere, the steam condenses into fine water droplets into which the entrained salts dissolve and ionize.

Abstract: A surge arrestor comprises at least one surge arresting element mounted between a pair of electrodes. The assembly is secured together longitudinally by a plurality of heat recoverable polymeric strands, and is contained within a heat recoverable shedded polymeric housing of electrically insulating and non-tracking material.

Abstract: In order visually to indicate the existence of a "continuation" current through a lightning arrester, an indicator is associated therewith, which is formed by an elastically deformable strip maintained retracted against capsule electrode by a retention mechanism which is associated with an electrical filter which causes fusion of a fusible wire under the effect of a "continuation" current. Once its end is released, the strip projects outwardly of the lightning arrester and marks the location of the defective insulation.

Abstract: A preferably low dielectric constant polymeric bonding layer is applied or bonded (i.e., laminated or coated) to at least one side of a preferably low dielectric constant polymeric delay line substrate. Preferably, the melting or softening point of the bonding film is lower than the melting or softening point of the substrate so that the application (e.g. lamination) step is carried out at a temperature which is above the softening point of the bonding film, but below the softening point of the substrate (thereby insuring the integrity of the delay line circuit). Thereafter, the delay line/bonding layer assembly is rolled up and head sealed so as to melt the bonding layer, thus heat sealing the delay line package. As the package heats up (in, for example, a tightly fitting die), the materials expand and provide sufficient pressure to bond the circuit together.

Abstract: A connecting apparatus includes a connecting conductor for connecting a supporting insulator supporting an overhead transmission line and a lightning arrester through a disconnecting member. The connecting conductor includes at least first and second conductor segments having given lengths. The first conductor segment connected to the lightning arrester is greater in bending strength than the second conductor segment connected to the disconnecting member.

Abstract: A high-voltage apparatus having a casing (1) filled with an insulating medium, an active part (6) connected to high voltage in the casing, and a pressure-relief valve (2) closing off the casing (1). The pressure-relief valve (2) includes a hinged cover (9) and a bending spring (12) acting on the cover (9). The pressure-relief valve (2) responds extremely quickly to changes in pressure of the insulating medium located in the casing (1). This is achieved partially by the fact that the bending spring (12) lies in the current path of the active part (6) connected to the high voltage and due to the fact that the bending spring (12) is formed with weakened regions which are heated faster by the current. As a result, the rigidity of this bending spring (12) suddenly drops as the current exceeds a predetermined value. This results in sudden relieving of the pressure in casing (1).

Abstract: In a metal-encapsulated gas-insulated high-voltage installation with an overvoltage arrester which is arranged in a separate encapsulation and is connected via a gastight feedthrough to the conductor of the high-voltage installation, fault arcs can lead to heavy stresses of the overvoltage arrester by dynamic forces due to overloading. In order to prevent this, there are provided in the connection between the feedthrough and the overvoltage arrester two electrode-shaped support bodies, between which a flexible current-carrying ribbon is arranged. The cross section of the current-carrying ribbon is designed so that it melts at currents of a magnitude which is equal to or larger than that required for the pressure relief of the overvoltage arrester after the arc has been blown out of the arresting housing. Thereby, the overvoltage arrester and the feedthrough are mechanically decoupled.

Abstract: A station protector for communication lines includes a line terminal formed for electrical connection to the communication lines and affixed to a base member of electrical insulator material. The base member has a well into which an arrester cartridge can be threaded. There is a grounding element affixed to the base member, the grounding element including an extending grounding member located outside the area of the well. A spring electrically connects the line terminal to a surge voltage arrester if an arrester cartridge is properly positioned in the well, and grounds the line terminal in the absence of the arrester cartridge or any part thereof.

Abstract: A protector module (30) for protecting the conductors of a telephone loop cludes a pair of protector assemblies (40-40') which are supported within a common housing (32). A gas tube voltage protection subassembly (42) of each protector assembly is connected electrically to a grounding subassembly (44) for causing current associated with excessive voltage surges to be conducted to ground. A first electrode includes a portion which extends through annular dielectric and metallic members and an opening of an open-ended metallic container (93) to engage a shunting element (62) of a current protection subassembly (41). The superimposed annular members are held in engagement with the first electrode at a substantially constant pressure by axial forces applied by turned-in portions (109--109) of a side wall of the metallic container. The shunting element is supported at one end of the line pin in an initial position by a fusible material.

Abstract: A protector module (30) for protecting tip and ring conductors of a telepe loop includes a pair of protector assemblies (40--40') which are supported within a common housing (32). A voltage protection subassembly (42) of each protector assembly is connected electrically to a grounding subassembly (44) for causing current associated with excessive voltage surges to be conducted to ground. Each protector assembly also includes a current protection subassembly (41) which comprises a dielectric base, as well as a tubular line pin (61) and a central office pin (57) which are connected together electrically. A shunting element (62) is disposed concentrially about and is supported at one end of the line pin in an initial position by a pellet (70) of a fusible material which extends between a closed end of the shunting element and an edge surface (68) of an open end of the line pin.

Abstract: A male base subscriber pair protector module in which substantially all of the internal components thereof are assembled upon an axially elongated base element prior to insertion within a module housing, thereby facilitating manufacture and allowing the use of a wide variety of existing components which are readily adapted for such assembly.

Abstract: A safety connector providing an overcurrent protective element, an overvoltage protective element and bimetal connecting terminals, in which the overcurrent protective element includes an upper terminal and lower terminal on the upper and lower part of the body, and which includes bimetal connecting terminals within the body, and a heating coil connected to the upper terminal and to a bimetal connecting terminal. Another bimetal connecting terminal is connected to the lower terminal. An overvoltage protective element is mounted on the bimetal connecting terminals on the electrodes and grounding electrode, respectively, and leading ends of the bimetal connecting terminals are placed to face each other.

Abstract: This invention relates to a compact protector which is used to prevent the over-heat of a compact motor used in heat generating appliances such as a hair dryer or electric washing machine. The protector incorporates therein an excess current prevention portion utilizing a bimetal and an excessive temperature rise prevention portion utilizing a temperature fuse. The protector opens an electric path by the double safety devices.

Abstract: A special zener diode is disclosed which is shunted across each cell in a series connected string of battery cells. In response to a cell failure which causes a cell to open circuit, all battery current is routed through the zener diode looping element. This current causes a permanent state change of the looping element thereby causing the looping element to become a permanent short circuit. Thereby, the failed cell is effectively removed from the circuit. Another embodiment is disclosed whereby the zener diodes are used to ensure uniform full charge among all of the cells in the battery. The zener diodes are chosen to have a breakdown voltage slightly higher than the optimal maximum battery voltage. A special charger is used which lowers the charging rate when the zener breakdown voltage is approached, so that the zener will not be destroyed from excess current during charging.

Abstract: An electrical component comprising a temperature responsive device including an electrically conducting member (1) of spring temper in contact with a thin insulating coating (3) of a substance which decomposes on being subject to an elevated temperature thereby allowing the conducting member (1) to effect a short circuiting operation. Suitably the conducting member (1) is coated with a thin layer of polyurethane varnish which vaporizes at the elevated temperature, and the conducting member (1) is arranged to engage contacts (5,5) under spring tension. In one embodiment the conducting member (1) is a wire of phosphor bronze or beryllium copper formed as a loop (2) with spring arms, the loop (2) being positioned on a pin 4 centrally disposed between spaced contacts (5) engaged by the arms under spring tension.

Abstract: A special silicon diode is disclosed which is shunted across each cell in a series connected string of battery cells. In response to a cell failure which causes a cell to open circuit, all battery current is routed through the diode looping element. This current causes a permanent state change of the looping element thereby causing the looping element to become a permanent short circuit. Thus, the failed cell is effectively removed from the circuit.

Abstract: An adaptor terminates one or more modular protectors of the same size obviating the need for a telephone company to carry an inventory of many different sizes. Each modular unit, which protects a telephone line, has a hollow shell into which two terminals are received, each terminal communicating with a protector. The terminals are elevated above a landing on the housing so that the distance between the two terminals exceed a predetermined distance to reduce noise. The protectors are enclosed within the hollow shell by a base cover which is secured in place by a grounding clip which has many tines on one end for penetrating the side of the housing; the other end of the grounding clip is so formed as to secure the housing to the adaptor.

Abstract: A protective device for use with a surge arrester to prevent fracturing of the porcelain body of a failed arrester includes a fast-operating switch which shunts a current-limiting fuse. The switch is operated by ignition of a chemical propellant charge, thereby rapidly diverting fault current to the fuse and additionally isolating the arrester from ground. The switch has a moving contact in the form of a gas-driven piston which strikes a separable terminal connected to a ground lead.

Abstract: A surge protection device which provides multiple back-up and tends to fail closed circuit or shorted is disclosed. The primary surge protection is provided by a gas break-down tube set to operate at one voltage level. A secondary or back-up surge protection is provided to operate at a higher voltage by means of a flat ceramic member sandwiched between the top of the tube and a cap that is affixed over the tube and ceramic member. The cap is sealed to the tube and the spacer end encloses a volume of air which is thus protected from moisture and dust. Upon failure of the gas tube, the back-up unit shorts surges across the shortest path between the cap and tube top, which path is adjacent a dielectric wall formed by the member. Discharge via this path tends to vaporize metal in the enclosed volume which upon redeposit on the ceramic surface tends to permanently short across that surface so that the device tends to fail closed circuit.

Abstract: A line protector device for providing an electrical conducting path between a line and ground upon an overvoltage appearing on the line includes an overvoltage device having a pair of longitudinally spaced conductive terminals forming an arc gap therebetween. One of the terminals includes a longitudinally extending portion and an insulation circumscribing the extending portion which is inserted into a longitudinally circumscribing shorting clip and is provided with a centrally disposed slit in one end which receives the extending portion of the overvoltage device. The clip and overvoltage device are received within a conductive cartridge which then may be inserted into a conventional terminal block.

Abstract: A circuit breaking device which comprises an elongate conductive element located within a casing and connected in series with a helical spring. The spring exerts a tensile load on the conductive element, and the conductive element is formed from a material such as copper which will yield and fracture mechanically under the influence of the tensile load when the conductive element is subjected to a current induced heating level greater than a predetermined level.

Abstract: A protector for telephone systems and similar systems is in the form of an elongate housing formed by two hollow box-like members, one fitting within the other. In the bottom member, a line terminal is provided at each end, each terminal connected to a line contact member in the housing. A ground terminal is provided at a mid position in the bottom member, connected to a support and ground member. A protector device assembly is mounted in the support and ground member, providing a breakdown gap connected between each line contact member and the ground. The device assembly can be two-electrode gas tube devices, a three-electrode gas tube device, or other devices. Back-up protector devices are positioned between each line contact member and the support and ground member.

Abstract: A module for the protection of multiwire lines against overvoltages comprises a casing formed by a receptable and a terminal carrier plate. The terminal carrier plate comprises a pair of terminals for each wire of the multiwire line, and an earth terminal. Overvoltage diverters are connected to said wires and each have a first electrode soldered to a U link which connects, the two terminals of each pair of terminals, and a second electrode soldered to a transverse bar itself soldered to an extension of the earth terminal. The subassembly connected to the terminal carrier plate is disposed within the receptacle and is potted in a plastic potting substance. This module may be used for the protection of telephone lines.

Abstract: A shunting element includes first and second electrical terminals for shunting an electrical component, a semiconductor component, and at least two electrically conducting parts partly formed in springs being electrically conductingly connected between the semiconductor component and one of the electrical terminals, the terminals being connected to each other with a low resistance through the electrically conducting parts when a current flows which raises the temperature in the semiconductor component to a given value.

Abstract: A heat protection device for overvoltage terminal block arrester magazines having with two-way arresters or with button arresters. According to the present invention, an S-shaped clip spring or an L-shaped clip spring is inserted in a button arrester of the 6.times.6-type or the 6.times.8-type. The clip provides one leg of the protection device having a solder preform and a switch contact to complete the circuit. In case of an overvoltage, the arc developed in the arrester causes the solder preform to melt off during an extended application of heat arising from the arrester, activating the switch contact and short-circuiting the leg of the arrester.

Abstract: In response to spurious signals in a circuit connecting telecommunications equipment with a serving central office, the signals will pass through terminals of a protector module and through a protector unit inserted in the circuit causing a lead pellet to melt or the air gap between carbon blocks to short and establish a path to ground so that the spurious signals may be grounded. When the protector unit is removed from the protector module, the circuit remains grounded until the protector unit is replaced. Alternatively, when the protector unit is removed, the electrical path of the circuit is opened by introducing an insulator in the path of signals between the terminals. In one embodiment, in the open circuit condition, unusually high voltages arc over from the protector terminals to a metallic pin and then to ground.

Abstract: A protective element system includes a distributor strip and a protective element pluggable into the distributor strip. The distributor strip has a plurality of terminal posts for insulation stripping connection to electrical conductors. A plurality of upwardly open receptacle chambers are provided in an upper part of the distributor strip. In each chamber, a pair of contact springs are connected to respective terminal posts at outer sides of the respective receptacle chamber. A portion of a grounding rail projects into each of the receptacle chambers between respective contact springs in the associated chamber. The protective element includes a plug portion for insertion into one of the receptacle chambers of the distributor strip. An upwardly open receptacle chamber is provided in the protective element for accommodating a pair of surge arresters. Contact springs are positioned opposite one another at outer portions of the receptacle chamber. A grounding rail projects into the receptacle chamber.

Abstract: A station protector for communication lines includes an electrical conductor formed for connection to the communications lines and affixed to a base member, a grounding means affixed to the base member, an arrester cartridge disposed in an aperture in the base member and a biased resilient member electrically coupling the electrical conductor to a surge voltage arrester or to circuit ground in the absence of the arrester.

Abstract: A three electrode gas tube protector has a central electrode and a line electrode positioned on each side, with a gap between each line electrode and the central electrode, the gaps being at a subatmospheric pressure. Connecting to each line electrode, in an axial arrangement, is a ground assembly having two coaxial conductive cups, their bottom ends spaced by a fusible member. A contact member is positioned within the inner cup and has a head and a stem. Around the stem is a compression spring, the stem passing through the bottoms of the cups and the fusible member. The end of the stem extends over the outer surface of the outer cup bottom, as by riveting. The spring is constrained between the bottom of the inner cup and the head of the contact member. On melting of the fusible member, the inner cup moves axially in the outer cup and a radially extending member, such as a flange or other, moves into contact with a ground member in a support structure.

Abstract: An arrester support and disconnector structure enclosed, in one embodiment, a cylindrical housing having a lower wall with a weakened zone. Electrically conductive members extend through the upper and lower walls of the housing and make electrical connection with the arrester and a ground wire, respectively. Between the conductive members is an explosive charge which is detonated by the passage of excess current, thereby removing the lower member. The cylindrical body has an exterior recess to receive a supporting strap. In another embodiment, the support structure includes an elongated nonconductive body mounted at one end to a conventional support bracket. At the other end an upper surface supports an arrester and a housing below that surface contains the disconnector, again containing upper and lower conductive members with an explosive charge therebetween. The housing surrounding the conductive members has a weakened zone which is separated when the charge is detonated by excessive current.

Abstract: An overvoltage surge arrester having an auxiliary breakdown path includes an elongated conductive electrode extension device received by one terminal of a gas tube arrester which has disposed thereon a pair of graphite washers with a mica washer sandwiched therebetween and a resilient insulating washer disposed between the extension device retaining head and one of the conductive washers. The other conductive washer is in intimate electrically conductive contact with the gas tube electrode that receives the electrode extension device. The assembly forms a creepage path in parallel with the surge arrester spark gap, when inserted into a conventional conductive cage and its associated tubular cap utilized with a station protector housing.

Abstract: A protector module, or assembly, for telephone lines and similar systems, has line terminals and a ground terminal in the base. The line circuit is between a related pair of line terminals. The line circuit includes part of a line bracket which extends up the side of the housing. The line bracket extends to the outer end of the housing and an aperture in the end of the housing permits access by a test probe to the line bracket. Normally, two line brackets are provided each associated with a pair of line terminals. A ground bracket also extends up the housing, being connected at one end to the ground terminal and having a flange at its other end. Between the outer end of the line bracket and the flange on the ground bracket a back-up or other form of protector member can be positioned.

Abstract: A station protector, particularly for telephone lines, has a housing with wells in which are positioned protector module assemblies, one for each line. Each line is connected to a basket member positioned in the bottom of a well and having cantilever legs extending upwards. A protector module assemlby is insertable in the top of each well and a bottom electrode of the protector module pushes down the basket member against a spring bias. If no protector module assembly, or if only a housing of such an assembly without a protector module, is inserted in a well, the basket member moves up and the legs move into contact with a metal collar at the top of the well, the collars connected to a ground terminal. The protector module assemblies connect to the metal collars, as by being screwed into position.

Abstract: Overvoltage arrester having a gas-filled housing wherein, spaced from one another by a tubular insulator, cylindrical electrodes ending frustoconically are disposed opposite one another and are formed, in a region of active surfaces thereof, with walls that are thicker than conical side walls thereof located in a region of transition to the insulator, at least one line of electrically conductive material being disposed at the inner surface of the tubular insulator and extending as an ignition line in direction from the one cylindrical electrode to the other, the electrodes and the insulator being receivable in a metallic sleeve acting as a socket at ground potential and having a movable surrounding cage, including a metallic sleeve for receiving the electrodes and the insulator, the sleeve serving as a socket and having a movable cage substantially concentrically and closely surrounding the electrodes and the insulator, one of the electrodes being a wire or pin electrode and the other electrode being a hollow