CA2066648C - Surge protector for telecommunications equipment - Google Patents

Abstract

A protector for protecting equipment, especially telephone equipment, against high voltage and/or current surges such as are caused by lightning in the vicinity of the equipment or the cables to which it is connected, comprises one or more overvoltage pro-tectors (42, 58; 234, 236) mounted upon one face of an insulating support (18; 218). A generally planar contact member (62; 290, 312) mounted upon the support member has a ground contact member (90; 296) to make contact with a ground electrode (114;
310) in the equipment to be protected and with each overvoltage protector. A spacer (60; 320, 322) of fusible plastics material cou-pled thermally to the protection device melts when a sustained fault occurs. As the spacer melts, it permits an electrical connect tion between the contact member and the line to which the over-voltage protector is connected, effectively short-circuiting the line to ground. Overcurrent protection may be provided by means of a resistor (116) disposed in series with the line and located close to the plastics spacer so as to heat the spacer when an overcurrent occurs. In one case, the spacer comprises a film (60) interposed directly between a pair of contacts (40, 74') which serve to short-circuit the protector. In another case, the spacer comprises a limb (324) with relatively thin lateral projections (328, 338) which melt and shear. In both cases, the spacer preferably comprises high density, high molecular weight polyethylene.

Description

2 0 6 6 6 ~ 8 PCT/CA90/00336 TITLE: ~SURGE PROTECTOR FOR TELECOMMUNICATIONS Et;UIPMENT

TECHNICAL FIELD:
This invention relates to protectors for protecting 5 equlpment against high voltages and/or currents such as are caused by lightning in the vicinity of the equipment or the cables to which it is connected. Embodiments of the invention are especially, but not ex~lusively, applicable to overvoltage protectors used for protecting telephone equipment.

BAC~GROUND ART:
Conventional such overvoltage protectors usually comprise a pair of gas tubes mounted coaxially within a housing. Fusible element-s, typical ly discs of solaer, are 15 associ ated one wi th each of the gas tubes . The arrangement is such that, when an overload conditlon persists, for example when a power line contacts the telephone line, the heat generated in the gas tube will cause the fusible element to melt and short-circuit the gas tube~, either directly or by releasing a spring-loaded plunger.
In U.S. patent specification number 4,056,840, issued November 1977, P.S. Lundsgaard et al disclose such a protector having coaxial gas tubes with a fusible dielectric pellet rnounted directly upon each gas -tube. Melting of the ~5 dielectric pellet allows a resilient conductive member to short-ci rcuit the gas tube.
In U . S . patent speci f i cati on number 4, 851, 957, issued July 1989, I<.H. Chung discloses a lead or plastics pellet mounted directly upon a gas tube. The pellet maintains 20666~8 a contact member away from the ele~ ,des of the gas tube.
When the pellet melts, the contact member short-circuits the gas tube.
US patent number 4,856,060 issued August 8, 1989 5 discloses a solid state protector in which solder preforms are urged against integrated circuit units by a shorting spring.
Melting of the solder preforms allows the shorting spring to ground the circuit.
An alternative overvoltage protector is disclosed 10 in U.S. patent number 4,212,047 by Napiorkowski, issued July 8, 1980, to which the reader is directed for reference.
Napiorkowski 9i crlosP~ a protector having a sleeve of fluoroplastics material around the gas tube and a clip of spring metal surrounding the sleeve. When a sustained fault 15 occurs, the heat generated causes the f luoroplastics material to melt, allowing the metal clip to contact the gas tube and effect the desired short circuit.
Another protector which uses a plastic insulator is rlosP~ in European patent application number 0018067 20 pllhli-hP~ October 29, 1980, which discloses a line protector for a ~ ications circuit comprising a varistor surge protector c~nnPctP~ between a pair of line pins and ground.
Electrically conducting spring clips span the varistor and are pressed towards its opposite faces. The spring clips contact 25 the ground pin contact of the varistor but are prevented from contacting the line pin contacts by an insulating sheet interposed between the clips and the line pin contacts. When a surge condition heats _the varistor sufficiently, the insulation melts permitting one or more of the spring clips to ground the line;
In practice, these known devices are susceptible to problems concerning the suitability of plastics materials for s use in overvoltage protectors of the kind used in tele ications, C~c:pc~r~ y in central offices and at subscriber's premises. As ~l;qc~lqs~d in U.S. patent speci~ication number 4,056,840, such protectors are designed to be "self -restoring" i . e . return to their open-circuit 10 condition once the fault has been cleared. Typically, such a protector can be expected to operate many times during a useful life of as long as ~orty years without being subjected to a fault severe e~ough and sustained long enough, to fuse the plastics material and short-circuit the gas tube.
15 Although such repeated operations do not generate enough heat to melt heat the plastics material, the plastics material nevertheless is sub; ected repeatedly to relatively high temperatures ~ecause it is in direct contact with the gas tube. This can lead to creepage of the plastics material and 20 to ~JL- l.ULe. failure.
The plastics material should also preferably exhibit a clearly de~ined and abrupt transition between its solid and molten states. The range of plastics materials which exhibit these characteristics and are capable of withstanding the 25 relatively high temperatures associated with direct contact with the gas tube or other protection device is limited.

DISCLOSUF~E OF TE}E INVENTION:

. ` ` 2066648 According to one aspect of the present inYention, a protector arrangement, for protecting t~ rhorl~ eguipment against excessive voltages, comprises:
a support member;
a protection device supported by said support member;
electrode means for coupling said protection device to the equipment to be protected;
mutually proximal first and second contacts biased one toward the other but maintained apart by spacer means of 10 thermoplastics material preventing electrical connection between said first contact and said second contact;
intercnnn~c~;n~ means connecting one t~nmin~l of said protection device to said electrode means and to said first contact;
a contact member connecting said second contact to a second terminal of said protection device and comprising a ground contact for connecting to a ground electrode;
the arrange~ent being such that excessive heating of the protection device causes the spacer means to melt and permit 20 electrical conn~rti~r between said first contact and said second contact, ~h~racterized in that said first and second contacts and the spacer means therebetween are spaced from said protection device, said interconn~r~i~rJ means providing a heat transfer path for conducting between said spacer means 25 and said protection device the heat required to melt the spacer .
Preferably the spacer comprises a high density, high molecular weight polyolefin, for example polyethylene. The spacer may comprise a f ilm.

. 2066648 Alternatively, the spacer may comprise a limb and at least one lateral projection abutting a heat-conductive element for transmitting heat from the resistance elementj one of the pair of contacts acting against the limb to urge it 5 towards the heat-conductive element, the arrangement being such that heat generated by an excessive current melts the spacer at the junction between the 12teral projection and the limb and the limb is displaced until the contacts make contact .
The support member, with the contact member assembled to it, may be housed in a housing having at least one aperture in a side juxtapo5ed to the support member. The ground contact portion may then be resiliently-biased to project through the aperture.
The support member may comprise a block of insulating material having a def lection temperature greater then the melting point of the spacer. The protection devics may be rl ~ cpoC~I in a recess in the block . /-/

In preferred embodiments of the invention, the support member has a pai r of mutual 7y-spaced protection devices, third and fourth mutually proximal contacts and a thermoplastics spacer maintaining electrical separation 5 between the thi rd and fourth contacts.
Second interconnecting means may then connect the thi rd contact to a terminal of the second protection device and to a second electrode means for connection to the equipment. A heat transfer path between the second protection 10 device and the second spacer provides for melting of the second spacer by heat generated by excessive current in the second protection device.
The contact member may have a second ground contact portion and the housing corresponding second aperture.
15 contact of the contact member.
The or each interconnecting means, conveniently a flat metal strip, may extend along one side of the member to the corresponding electrode means. Where two protection devices are provided, their respective in-terconnecting means 0 may extend along opposite sides of the support member.
Preferably the or each protection device is a solid-state dev i ce .
Aspects of the invention also concern protection against excessive or so-called sneak current. In 25 telecommunications equipment there is a need for protection against relatively low level current surges which are not accompanied by a voltage surge sufficient to operate the usual overvoltage protector but nevertheless can still damage the te l e commu n i cat i on s equ i pment . To sat i sf y t h i s need, sneak .:

current protectors are used which incorporate a current sens i t i ve e l ement .
. Known sneak current protectors employ a heat coi l which fits into a three dimens10nal space frame. The heat 5 coil comprises a resistive wirel ln series with a telephone line or the like, and wrapped around a spool. A spring loaded plunger is sQldered into the spool. When excessive current causes: the heat coil to heat up, heat is transferred to the solder causing it to mel~ and the ~plunger to short the 10 telephone line to ground, thereby shunting the excessive current away from the equipment. Usually, in an overvoltage protector of the gas tube kind described above, the heat coils are wound around the plunger and melt the same solder discs as the gas tubes.
Such known sneak current protectors are not ent~rely satisfactory because they involve a relatively complex set of thermal masses and conduction paths. Their current protection levels are not easy to change and the protectors usuaily have to be custom made for each application which increases 20 production costs.
Accordingly, protectors embodying the first aspect of the invention may further comprise a substantial iy planar resistance element, for example a ceramic ~chip resistor, connected to the electrodes so as to be in series wtth a line '5 tQ be protected. The resistance element may be disposed in thermal proximity to the spacer of thermoPlastics material.
According to a second aspect of the invention, a protector for protecttng equipment aga1nst excessive overvoltages and excessive currents--comprises~

.~

7 20~6g'8 an overvoltage protection device;
a pai r of electrodes for connecting the protector to equipment to be protected;
interconnectin3 means connectin3 respective ones of said 5 pair of electrodes to one terminal of said protection device;
a contact member for connectlng a second terminal of said overvoltage protection device to a ground electrode of the equ i pment;
first and second contacts connected to respective 10 terminals of said protection device and biased one towards the other;
a thermoplastics sPacer maintaining separation of said f i rst and second contacts, a substantially planar resistance element connected in 15 series between one of said electrodes and said one termlnal of sald overvoltage protection device;
the interconnecting means servins to conduct heat from both said resistance element and said protection device to said thermoplastics spacer; and 20 =: the arrangement being such that excessive heating of either one of the resistance element and the protection device causes the spacer to melt and perm1t contact between said f i rst and second contacts.
The spacer may comprise a central 1 imb and at least ~5 one lateral projection or arm, and comprise a fusible material. The projection may t'hen abut a heat-conductive element connected to the resistance element, One of the pai r of contacts acts agalnst the central 1 imb to urge it towards the heat-conductive element. When an excessive current in the , ~? = 8 resi stance el ement heats the SPacer suff i cient1 y, the pl asti cs material at the junction between the 7atera7 projection and the central limb melts and the centra7 limb is displaced until the contacts meet.
In preferred embodiments of the second and third aspects of the invention, the resistance element is mounted upon a substrate, for example a printed circuit board, and the interconnection means comprises printed circuit elements connecting the resistance element in series with the equipment 10 to be protected. The plastics spacer is also mounted upon the printed circuit board or substrate.
The 7ength and cross-sectioned area of the printed circuit e7ements may be controlled to compensate for different amounts of heat generated in the protection device and the 1~ resistance element respectively.
According to another aspect of the invention, a protector for protecting against e~cessive currents in telecommunications equipment comprlses a reslstance element and electrodes for connecting the resistance e7ement in series 20 with a 1 ine to the equipment which is to be protected, such pair o~ contacts being mutually pr4ximal and biased one towards the other but maintained apart by an insulating spacer. The spacer comprises a central limb and at least one lateral projection or arm, and comprises a fusible material.
~= The projection abuts a heat-conductive element connected to the resistance element. One of the pair of contacts acts against the central 1 imb to urge it towards the heat-conductive element. When an excessive current in the resistance element heats the ~pacer sufficiently, the plastics WO 91~05387 ~PCT/CA90/00336 9 2066~8 materlal at ~he junction between the lateral projection and the central limb melts and the central limb is displaced until the contacts meet.
According to yet another aspect of-the invention, 5 a protector fo-r protecting telephone equipment against excessive voltages comprises:
a support member supporting an overvoltage protection device;
electrode means for coapling~ said protection device to 0 the equipment to be protected;
interconnecting means connecting one terminal of said protection device to said electrode means and having a first contact;
a contact member comprising a ground contact for 5 contacting a ground electrode extending adjacent said protector when the protector is installed in said equipment and a second contact juxtaposed to said first contact, said first contact and said second contact being biased one toward the other;
a spacer of thermoplastics material separating said first contact and said second contact, said spacer comprising a ~imb and at least one lateral projection, the projection abutting a heat-conductive element for transmitting heat from the protection device, one of said first a=nd second contacts 25 acting against the limb to urge it towards the heat-conductive element, the arrangement being such that said excessive heating melts the spacer at the junction between the lateral projection and the l imb permitting the l imb to displace unti l the f i rst and second contacts make contact .

WO gl/05387 PCI/CA90/00336 ~o~;6~8 ~

BRIEF DESCRIPTION OF DRAWINGS:
An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawin3s in which:-~ Figure 1 is an exploded isometric view of a protector for use in equipment in a teleFhone central office f~nd having a thermal shunt;
Figure 2 is a plan view of a planar spring metalcontact member of the protector showing current flow in the 10 contact member after operation of the thermal shunt;
Figure 3 is a cross-sectional view on the line 3-3 of Figure 2;
Figure 4 is a fragmentary cross-sectional view on the longitudinal centre line of the protector; and Figure 5 is a detail view illustrating an embodiment of a second aspect of the invention;
Figure ~ is a view of a protector according to a th i rd aspect of the i nvent i on:
Figure 7 is a plan view of the protector of Figure 20 6;
Figure 8 is a view corresponding to Figure ~i after the protector has operated:
Figure 9 is an end view of a detail before operation of the protector;
Figure 10 is a view corresponding to Figure 9 but af te r ope rat i on of the p rotecto r ' Figure 11 is a sectional partial view of the protector after operation; and 11 206664~
Figure 12 is a plan~Yiew of a printed circuit board assembly of the protector of ~Figure 6:.

5 MODE~S) FOR CARRYING OUT THE INVENTION:
Referring to Figure 1, an overvoltage protector for use in protecting equipment in a telephone central office comprises a housing 10 in the form of an elongate box, of square cross-section, closed at one end and open at the other.
10 A handle 12 pro~jects from the closed end. Adjacent the same end, a lever 14 extends generally parallel to the housing 10 and terminates in a lip 16. The lever t4 has a depending detent (not shown) which serves to limit withdrawal of the protector from the equipment at a predetermined position until 15 the lever 14 is flexed to disengage the detent.
In its surface shown uppermost in Figure 1, a support member 18 of generally parallelepiped shape has two recesses 20 and 22, respectively, spaced apart along its length, w7th a shoulder or land 24 between them. The housing 20 10 and support mernber 18 are made of insulating material, for example a synthetic plastics material 8uch as Valox 420SEO
(Trade Mark), a polyester by General Electric Corporation.
An interconnecting member, in the form of a flat copper strip 26, extends along one side of the support member 18 between 25 the shoulder or land 24 and a U-shaped groove 28 in the side of the support member 18. The groove 28 houses a U-shaped electrode 30 such that its l imbs 32 and 34 protrude from the end of the support member 18 that wi l l be adjacent the open end of housing 10 when installed. The limbs 32 and 34 serve WO 91tO5387 PCT/CA90/00336 ~ 6~8 12 - --as electrodes or contact pins to mate with complementary contacts in the equipment cabinet when the protector is i nstal l ed .
The interconnecting strip 26 overlaps the U-shaped 5 electrode 30 and is connected to it by crimping or soldering as at 36. The interconnecting str~p 26 has two tabs 38 and 40, respectively, formed by bending the edge portions of the interconnecting strip 26 at right angles. Tab 38 extends along the bottom of recess 20 and tab 40 projects inwardly a 10 short distance across the upper surface of shoulder or land 24. Tab 40 serves as a contact, as will become apparent in the ensuing description. A solid state overvoltage protection device 42 is accommodated in recess 20 and rests upon contact tab 38. The sol id state overvoltage protection device 4Z
15 comprises two metal discs 42A and 42B, the latter larger than the former, which serve as terminals. The actual solid state deYice, typically a voltage-triggered semiconductor device providing bi-directional overvoltage protection, is sandwiched between the metal di scs 42A and 42B.
o =, A second interconnec~ing strip 44 extends along the opposite side of t~le support member 18 and is similar to interconnecting strip 26 in that it has a contact tab 46 projecting inwardly a short distance across shoulder or land ~ 24 and is connected to a U-shaped electrode 48 housed in a ''5 groove bO. The 1 imbs 52 and 54 of the U-shaped electrode 48 project from the end of the support member 18 in a similar manner to l imbs 32 and 34.
The second interconnecting strip 44 differs from the first interconnecting strip 26 in that its second cor'tact tab , .

13 20666~8 s6 eYtends across the bottom of the second recess 22. A
second solid state overvoltage protection device 58, similar to device 42, rests upon tab s6 in recess 22. The dimensioning of the recesses 20 and 22 and the solid state 5 overvoltage protection devices 42 and 58 is such that the upper faces of the devices 42 and 58 are rlush with the upp~ l_ sur~ace of the support member 18.
A film 60 of synthetic plastics insulating material, specifically high density, high molecular weight polyethylene, 10 for example SCLAIR WCI 46C (Trade Mark) resin by Du Pont Inc., which has low creepage, eYtends across the upper surface of cho~ lPr or land 24 of support member i8 and is clamped between it and the underside o~ a contact member in the form of a spring contact plate 62. This spring contact plate 62 15 is ~ormed, conveniently by stamping and/or chemical milling, from a piece of flat stock beryllium-copper, or other suitable resilient contact material, as illustrated in Figure 2. The contact plate 62 comprises a medial portion 64 deformed out-of-plane to ~orm two semi-cylindrical thermal shunt springs 66 and 68, respectively, one each side of a central hole 10.
The side margins 72 and 74 of medial portion 64 o~ the plate 62 serve as load distributors, eYtending longi~ n~l ly to overlap, and bear against, the underlying portions 72 ' and 74', respectively, of the plate 62.
Each distal portion of the contact plate 62 comprises three limbs 76, 78 and 80, respectively. Each middle limb 78 is generally T-shaped and arched, a lateral piece 82 at its eYtremity forming the cross bar of the "T"
bearinq against the adjacent end portion~ o~ llmbs 76 and 78.

WO 91/OS387 , 8 PCI/CA90/00336 ~0 1 4 ;~ i~ '~
The spring contact plate~62 and plastics film 60 are clamped to the ~support member 18 by a fastener in the form of a screw 84 which extends through the hole 70 ln the spring contact plate 6 and a corresponding hole 86 in the plastics film 60 S and into a screwthreaded hole 88 in the middle of shoulder or l and 24 of support member -18 . ~
The edge portions 72' and 74' beneath the load distributors, marginal portions 72' snd 74', respectively, , overl ie contact tabs 46 and 40 and serve as contacts also.
10 Contact tab 40 forms with contact portions 74' a first pair of contacts. Contact.tab 46 forms with contact portions 72' a second pair of contacts. The edge portions 72' and 74' are biased towards the support member (downwards in the drawing) by the associated thermal shunt springs 66 and 68, 15 respectively. Thus, when screw 8i is tighténed, the thermal shunt spr~ngs 66 and 68 are deformed both elastically and plastically into their finar position to obtain maximum and consistent spring trave~ ard force. The plastics film 60 is clamped resiliently between contact plate 62, specifically the 20 marginal contact portions 72' and 74', and contact tabs 40 and 46, and the solid state overvoltage protection devices 42 and 58 make good eiectrical contact with the underside of the contact plate 62 as shown in Figure 4.
With the spring contact plate 62 and plastics film 25 60 assembled onto the support member 18, the assembly can be sl id into housing 10. The arched 'portions 90 and 92 of middle limbs 78 of spring contact plate 62 will protrude through elongate longitudinal slots 94 and 96, respectively, in the juxtaposed wall of housing 10, as illustrated in Figure 4.

~ , .
- ' :

WO 9t~05387 PCT/CA90/00336 lS - ~OS6648 An end cap 98 has four holes 100, 102, 104 and 106 to receive the contact pins 32, 34, 62 and 54, respectively, when the end cap 98 i s f i tted onto the end of support member 18 in housing 10. Lugs 108 (only one is shown) protrude 5 laterally from the edges of end cap 98 to engage in holes 110 in extensions 112 protruding from the side walls o~ housing 10 and secure the assembly in the housing 10.
In use, contact pins 32 and 34 will be connected to the 'tip conductor and contact pins 52 and 54 will be 0 connected to the ring' conductor of the telephone line. The protruding arched limbs 90 and 92 of spring contact plate 62 will make contact with a ground plane 114 (see Figure 4) in the equipment cabinet. When an overvoltage occurs on the 'tip' conductor, solid state overvoltage protection device 42 15 will operate to short-circuit the tip conductor, by way of interconnecting strip 26, to ground plane 114. If the overvoltage condition is sustained, the heat generated in the solid state overvoltage protection device 42 will be transmitted via tab 38 to tab 40 and to contact plate 62, 20 eYentually causing the plastics film 60 to melt. In view of the pressure applied by screw 84, the plastics material between the tab 40 and the spring contact plate 62 will be exuded, allowing electrical connection between the tab 40 and the spring contact plate 62 to ground the tip, effecting 25 mechanical short-circuiting of the overvoltage protection device 42. Fig~re 2 shows the directions in which current flows in the spring contact member 62 following a fault affecting the tip conductor.

_ ~ 20666~8 If the overvoltage occurs on the "ring" conductor, overvoltage protec~ion device 58 will operate, sustained fault conditions leading to ~elting of the plastics film 60 trapped between tab 46 and contact plate 62 to effect the short-5 circuit.
The way in which the spring contact plate 62 is formed is particularly advantageous. The T-shaped ends 82 of limbs 78 can slide along the surface of outer limbs 76 and 80 as the curved portions 90/92 are fleYed. This helps to ensure 10 even distribution of the spring pL~S~.-lLe and consistent contact with the ground plane. II~L-~uv~:r, this bifurcate contact between limbs 78 and limbs 76 and 80, shares current flow, increasing current carrying capacity as compared with a single contact.
Likewise, the marginal portions 72 and 74 of the spring contact plate 62 can slide relative to the underlying edge portions 72' and 74' of the limbs 80 upon which they bear. This ensures that, as screw 84 is tightened, the force is applied evenly and directly above the ~_ULL~ in~ tabs 20 40 and 46 so that there is little risk of an edge penetrating the plastics ~ilm 60 as a result of uneven force distribution.
Two protrusions may be provided on the underside of the spring contact plate 62, each positioned to bear against one of the overvoltage protection devices 42 and 58. The 25 protrusions will improve contact and provide a slight clearance, typically about 0.5 mm., between the top of the overvoltage protection device and the spring contact plate 62.

W(> 91/05387 PCT/CA90/00336 ~ 21 Referring now to Figure 5,= which shows an overvoltage protector with an alternative form of contact member and means for protecting against excessive or sneak'' current, the overvoltage protector is generally similar in 5 construction to that described with reference to Figures 1 to 4, but with "sneak" current protection means for-protecting against excessive currents. Components corresponding to those shown in earlier Figures are identified by the same reference numerals but with the suffix 'A".
One significant difference comprises the spring contact member 62A, which is formed by two strips of spring contact material 63 and 65, the medial portions of which are riveted or welded together as at 67 and extend the ful 1 width of the support member 18. Spring contact strip 65 thus 15 extends between spring contact strip 63 and the plastics material 60 on shoulder 24 of the support member 18. Spring contact strip 65 projects both sides of the shoulder 24 to overl ie and make electrical contact with the sol id state overvoltage protection devices 42A and 58A, respectively.
20 Spring contact strip 63 arches away from spring contact strip 65 to form two arched contact portions 90A and 92A to contact the ground plane 114 (Figure 4).
Another significant difference is that a pair of planar resistance elements in the form of ceramic chip 25 resistors 116 (only one is shown) are Positioned adjacent the medial shoulder or land 24 of support member 18, one such resistor each side of the central fastening screw 84. Each ceramic chip resistor 116 is housed in a recess 118 in the side of the support member 1~3. Instead of a single connector ~o666~ 18 strip 26, the interconnection for ~he "tip" conductor is made by conductors 120 and 122, respectively. Conductor 120 is connected at one end to a~~electrode in the form of contact pin 34A and conductor 122 is connected to an electrode in the form of contact pin 32A. The contact pins 34A and 32A are separate and replace the single U-shaped electrode 28 shown in Figure 1.
~ onductor 120 has a first tab 38A extending beneath sol id state overvoltage protector i2A and a second tab 40A, 10 serving as a contact, extending across shoulder or land 24 beneath the thermoplastics f~lm 60. An extension 124 extend6 from contact portion or tab 40A to overl ie and contact one terminal 126 of the ceramic chip resi6tor 116. The other conductor 122 extend6 longitudinally of the 6upport member 18 15 to connect to the other terminal 128 of chip re6i6tor 116.
Both conductors 120 and 12 ' may be sol dered to the respecti ve underlying terminals 126 and 128 of the chip resistor 116.
The chip resistor 116 is thus connected between the contact pins 34A and 32A and hence in series with the "tip"
20 conductor of the teiephone 7ine. Should a fault occur which is characterized by a sustained abnormally high current in the line, a so-called "sneak current", but not necessarily accompanied by a voltage high enough to operate the overvoltage protectors 42 and 58, the heat generated in the 25 chip resistor 116 will be conducted via extension 124 at the conductor 120, to tab contact 40A, to melt the plastics film 60, and connect the contact~ tab 40A to the spring contact p1ate 62, short-circuiting the protector.

.

W~ 9l/05387 PCr/CA9P/00336 It should be apprec~ated that the connections at the opposite, "ring", side of the support member 18 will be bifurcated in a similar manner and the second chip resistor inserted in series with the ring" conductor. An overcurrent - 5 or "sneak current" in the "ring" line will result in overheating of the second chip resistor to melt the Plastics film and short-circuit the "ring'' conductor to ground in a simllar manner to that described for the "tip" conductor.
A potential limitation of protectors in which a thin 10 plastics ~ilm is interposed directly between the contacts which are to short circuit, is that the thermal impedance of the film is relatively low, and becomes even less as the film begins to melt and the contacts begin to close. Hence the ground contact can act as a heat sink and lnhibit the heating 15 of the film to its meltlng polnt. This could be a problem when the source of the heat is a sneak current. The embod i ment d i sc l osed i n F i gu res 6 to 12 add resses th i s i ssue .
Referring now to Figure 6, a combination overvoltage and overcurrent protector is shown with a housing 210 which 20 is similar to the housing 10 shown in Figure l. The housing 210 takes the form of an elongate box of square cross-section, closed at one end and open at the other. A handle 212 projects ~rom the closed end. Adjacent the same end, a lever 214 extends generally parallel to the housing 210 and 25 terminates in a lip 216. The lever 214 has a depending detent (not shown) which sarves to limit withdrawal of the protector from~the equipment at a predetermined position until the lever 214 is fleXed to disengage the detent. The protector comprises a generally parallelepiped support block 218 which . ` ` 2~66648 has one surface ~that shown uppermost in Figure 6) stepped to provide in d~r~n~ing order, four steps 220, 222, 224 and 226 (see also Figure 7), respectively, with an inclined face 228 between step 224 and step 226. Two e~ ~:sses 230 and 232 are 5 provided in steps 220 and 224, respectively. The recesses 230 and 232 house overvoltage protectors 234 and 236, respectively .
Interconnecting members 238 and 240, respectively, extend along the side of the support block 218 which is 10 recessed to ac~ '-te them. The interconnecting members 238 and 240 comprise wire rod. At one end, the int~-o~ e~ Ling members 2 3 8 and 2 4 0 extend beyond the end f ace of the support blocX 218 and protrude through an end cap 242 as electrode pins 224 and 246, respectively. When the protector is 15 installed in the equipment cabinet, electrode pin 244 will connect to outside plant and electrode pin 246 will connect to a line to the central office.
Interconn~cting member 240 has a tab 248 (see Figure 7) which pro~ects into recess 232, beneath overvoltage 20 protector 236, and maXes contact with one t~rm;nll of the over-voltage protector 236. A cuL~ n~1;nq tab 250 (see Figure 7) of a ~OrL~ l;n~ inte~ u..l.e~ Ling member 252 on the RING side of the support bloc3c 218 extends into recess 230 to make contact with overvoltage Conn~ct~r 234 in like manner.
25 Adjacent its end remote from the electrode pin 246, int~:L~ ul~lle~_Ling member 240 has a section which extends perpendicularly and terminates in a connector pin 254 which has a reduced diameter. The r~nnnct,~r pin 254 extends into a t~rmi n;-l post 256 soldered into ~ printed circuit board 258 which i5 mounted upon the lowermost step 226 adjacent the end of support block 218. A ceramic chip resistor 260 is surface-mounted upon the printed circuit board 258 and has one te~rrin~l cnnn~ 1 ed by printed circuit conductor 262 to 5 terminal post 256. The other terminal of chip resistor 260 is connected by printed circuit conductor pad 264 to a second tPrminAl post 266 which is mounted upon the printed circuit board 258. A connector pin 268, formed as a reduced~ r ~r section of interconnecting member 238, protrudes into tPrmlnAl 10 post 266. Hence, the chip resistor 260 is connected in series between the electrode pins 244 and 246, respectively, 2nd hence in series with the line hetween the central of f ice and the outside plant once the protector is installed.
A second chip resistor 270 is mounted upon printed 15 circuit board 258 and is c~nn~ct~d in series with the other wire of the line. Thus one terminal of chip resistor 270 is connected by printed circuit conductor 272 to a terminal post 274 which receives a connecting pin 276 o~ int~:r- u..n~_-ing member 252. ~rhe other terminal of chip resistor 270 is 20 connected by printed circuit conductor pad 278 to a t~rmin;~l post 280 which receives a connecting pin 282 formed at one end of an interconnecting member 284. The ends o~ intt:r~_o~e~ Ling members 252 and 284 remote ~rom the printed circuit board 258 protrude through end plate 242 as electrode pins 286 and 288, 25 respectively. Hence, chip resistor 270 is connected in series between electrode pins 286 and 288 and hence in series with the line between the central off ice and the outside plant.
A spring contact member 290 overlies the support block 218 and is fastened to it by a central screw 292. The ~ 20666~8 spring contact member 290 has three finqer portions 294, 296 and 298 at one end and three finger portions 300, 302, 304 at the other end. Middle fingers 296 and 302, respectively, curve away rrom the support block 218 to protrude through 5 respective slots 306 and 308 in the housing 210. In use, the curved fingers 296 and 302 will make contact with a ground plate 310 of the ~1 i L into which the protector i8 installed .
A bifurcate contact plate 312 has a bight portion 10 314 at one end which is clamped between spring contact member 290 and the step sur~ace 222 o support block 218. The limbs 316 and 318 of the bifurcate contact plate 312 extend longitll~;nllly o~ the protector to a position above the printed circuit board 258. Their distal ends are supported 15 by plastic spacers 320 and 322, respectively, so that limbs 316 and 318 extend adjacent, but not touching, connecting pins 276 and 254, respectively. The contact plate 312 is resilient, ~or example spring metal, and so shaped that the limbs 312 and 318 are urged towards the adjacent ends Or 20 connecting pins 276 and 254 but prevented rrom contacting them by the plastic spacers 320 and 322, respectively.
Figure 9 is a detail diagrammatic end view of the printed circuit board 258 showing the limbs 316 and 318 o~
contact plate 312 supported by plastic spacers 320 and 322, 25 respectively, in the normal or "open-circuit" position. The plastics spacers 320 and 322 are o~ cruciform shape, having central limbs or "web" portions 324 and 326, respectively, and lateral arms 328/338 and 330/331, respectively. The web portions 324 and 326 support, at one end, the contact plate WO 9t~05387 2 0 6 6 6 ~ 8 PCT/CA90/00336 23 ~ :
limbs 316 and 318, respectively. Thei~r opposite ends extend a small distance into corresponding holes 332 and 334, respectively, in the printed circuit board 258. The lateral arms 328 and 329 of spacer 320 rest upon the subjacent printed 5 circuit conductor sections 336 and 338, respectively, and support the spacer 320 against the spring force exerted by the contact plate limb 316. In like manner, lateral arms 330 and 331 of apacer 322 rest upon subjacent printed circuit conductor sections 333 and 335, respectively.
Figure 12 shows the conductor pattern of the printed circuit board 258 in more detail. Conductor 262 has at one end a solder pad area 340, to which the terminal post 274 Will be soldered, and at its other end a conductor pad 342 to which one term~nal of resistor 260 is soldered and which extends to 15 join pad 335 beneath the lateral arm 331 of spacer 322.
Conductor pad 264, the bonding pad for terminal post 266, is connected to a second bonding pad 346 for the other terminal of resistor 260. Portion 333 which extends between the resistor bonding pad 346 and terminal pad area 264 and beneath 20 the arm 330 of spacer 322, is relatively wibe as compared with conductor 262. Conductor 262 which interconnects the resistor bonding pad 342 and the terminal bonding Pad 340, is relatively long and narrow. The width of the conductor strip 262 and its length, are selected so that the thermal 25 resistance between the terminal pad 340 and the resistor 260 i s much greater than that between the spacer 322 and the resistor 260. This determines the sensitivity of the sneak current protection by controlling heat sink effects due to the thermal mass of ground electrode 114 (Ftgure 4) (318 in Figure WO 91/05387 2 0 6 ~ 6 4 8 PCr/CA90/00336 7). The interconnecting member 240, connects pad 340 to SSOVP
236 which in turn is connected by contact member 2gO to sround electrode 310, which is, in effect, a virtually infinite heat sink. On the other hand, in-terconnecting member 238 connects 5 pad 344 to electrode 244 which, in use, is connected to wiring having a relatively low heat sink effect.
Conductors 272 and 278 associate~ with resistor 270 and spacer 320 are formed in a similar way to conductors 262 and 264 and so wi 11 not be descri bed i n detai l .
A through slot 348 extends down the middle of the printed circuit board 258 to provide thermal isolation between the resistors 260 and 270.
When an overvoltage condition operates SSOVP device 234 heat is conducted via printed circuit conductor 272 to 15 conductor section 338 to heat arm 329 of spacer 320. Heat is also transmitted by way of resistor 270 to conductor section 336 to heat the other arm 328 of the spacer 320. When SSOVP
device 236 operates, heat is transmitted in like manner via printed circuit conductor 262 to heat the lateral 330 and 331 20 of spacer 332.
When an excessi ve ( sneak ~ current heats one of the resistors 270 and 260, the heat is conducted by printed circu;t conductors 333 and 335, or 336 and 338, directly to the lateral arms 328 and 329, or 330 and 331 of the associated 25 spacer 320 or 322. When sufficient heating has occurred, the lateral arms 328 or 330 melt= or shear~w=ith a snap action from the associated web portion -324 or 326. The associated limb 316 or 318 of the spring contact plate 312 displaces the web portion 324 or 326 into the corresponding hole 3,2 or 334 WO 9l/05387 ~ ,PCr/C~90/00336 ~ 25 206664~
until the ~imb 316 or 318 make& contact with the corresponding connector pin 254 or 276 to short circuit the associated RING
or - TIP to ground. Figures ~0 and 11 i1lustrate such displacement of spacer 320 permitting contact between limb 318 5 and~connecting pln 254.
As mentioned previously, the ground electrode 114/318 in the equipment is, in effect, a virtually infinite heat sirk and the contact plate 312 is connected to it. The height of the central limb of the spacer provides thermal 10 insulation between the contact plate 312 and the resistance element. This ensures that the heat generated by the resistance element is avai lable to melt the lateral projections.
It should be appreciated that an overvoltage 1~ protector will usually produce more heat, when conducting, than a resistance element conducting a sneak current.
In the specific embodiment of Figure 6 - 12, the spacers 322 and 320 straddle conductor sections 333/335 and 336~338, respectively, and hence are in paralle1 with the 20 corresponding resistance element 268 or 270. Consequently, heat from the protector is transmitted to one of the lateral arms via the associated resistance element and directly to the other l ateral arm . A mod i f i cati on i s env i saged i n wh i ch both arms of each spacer rest on the same conductor section and 25 hence are both heated to the same extent. This entai ls enlarging conductor sections 338 and 335 to encompass the holes 332 and 334, respectively, and provide an area of conductor around the hole to ~ontact both arms of the spacer.

WO 91/05387 PCr/CA90/00336 j 20~,~66~ 26 -~ ~
A separate conductor would connect the resistance element to i ts assoc i ated te rm i na l pad .
The chip resi~stor could be stocked in various values and readily substituted during manufacture to allow economical 5 manufacturing of protection~devices with different current ratings. These advantages are not real ised by existlng protectors which employ heat coils in the form of wire-wound resistors around plunger pins of gas tube protection devices.
of course, being planar itself, the ceramic chip resistor is 1u partlcularly advantageously employed in a protector which employs general ly "planar" or "epitaxial " components as disclosed hereinbefore.
In the afore-mentioned US patent number~4,û56,84û, the plastics film is required to protect the gas tube against 15 failing open circu~t. Embodiments of the present invention protect the plastics support member 18 and plast1cs housing 10 against overheating.
The characteristics of the plastics material used for the spacer ~film 6û, cruciform spacers 320, 322~ are "O determined according to the operating requirements of the device. ~Thus, since Valox 4205E0, the, material of the support member (18, 218?, has a heat deflectior temperature of about 2ûûC, and the typical maximum, environmental temperature is about 70C, the p1astics spacer must melt at a temperature in ~5 the range 70-20û~C. A melting temperature closer to the upper end of the range is preferred sir~ce the device would then be less suscepti~le to early demise due to AC faults. Especially where a thin fi lm, preferably about O.û02 inches, is employed so as to minimize travel of the thermal spring shunt, good . , , ,,, ,, , , , _,, _ _ _ _ , 2~66648 dielectric strength, greater than 20 kV/mm., is required as also is good creep resistance since the usual design life o~
such a device is about 40 years. Similar considerations apply to the lateral arms 328, 329, 330, 331 since they also are 5 relatively thin as compared to the length of the central limb 324, 326 which is intended to provide good thermal insulation between the c~n~ tn~s 333, 335, 336 and 338 and the contact limbs 316 and 318. The preferred material, high molecular weight, high density polyethylene, meets these reguirements.
10 The specific material described herein (SCLAIR WCI 46C) has a melting point of about 125C, dielectric :~Lreh~h of about 200 kV/mm., low creep rate, is available in thin fil~s, and the products of its combustion are not corrosive or particularly toYic.
SCLAIR WCI 46C is a polyolefinic polymer of the polyethylene class. It has a clearly defined melting point at the required temperature. It also keeps its conformation requirements up to the melting ~ ~Lu.,as. Other polyethelynes, indeed other polyolefines such as polypropylene 20 or polybuteric, can be used providing that the degree of crystallinity, stereospeci~icity and molecular weight combine to give the reguired thermal and mechanical properties.
Other polyolefins might also be suitable. A high density, of at least about 0.941, has been found to give a 25 suitably clear and guick transition between the solid and li~uid states. For those ~mho~ ts of the invention in which the plastics spacer is in the form of a film, manufacturing limitations may limit the specific gravity to about 0.g65. A high molecular welght, ~t lea~t ~5O,o00, has -WO 91~05387 PC~CA90)DD336 ~ -206664~ 2~ --been found to provide the necessary strength to meet the long ~term creepage re~ui rements, == It is enYisaged that other crystalline po1ymers, such as nylon, could be used since they exhibit a clearly 5 deflned melting point. However, because they melt at a higher temperature than SCLAIR hlCI 46C, the other components used in the protector, particularly the synthetic plastics support member 18, 218, would need to tolerate the higher temperature.
It will be appreciated that, where a synthetic plastics 10 support member is used, its heat deflection temperature should be greater than the melting point of the thermoplastlc spacer or film.
Further simpl if ication and economy might be achieved by laminating the plastics film to the spring contact plate 15 before assembly. Moreover, the end cap could be an integral part of the support member. In the case of the embodiment of Figure 5, the two parts of the spring contact member 62A might be clamped together by means of the screw 84A rather than we 1 ded or r i veted .
It should be appreciated that the spring contact members 62 (Figures 1-4~ and 62A (Figure 5) are interchangeable, regardless of whether or not the overcurrent resistors are incorporated.
It should also be appreciated that the sneak current ''5 protector could be used alone.

INDUSTRIAL APPLICA~ILITY:
An advantage of spacing the fusible thermoplastics spacer away from the actual overvoltage protection device is , WO 91/05387 2~ n ~ ~ 6 ~ ~ PCI'/CA90/00336 that the thermoPlastics material may have-- a~ ~ower meltlng point than, for example, fluoroplastics. Even though the contacts juxtaposed to the spacer or film are connected to the terminal of the protection device, the interconnection will 5 limit heat conduction. This enables materials to be used which have a lower melting point and which do not produce corrosive byproducts of combustion. Polyethylene is such a mater i al .
Fluoroplastics, such as are disclosed in the cited 10 patent specifications, have a poorer resistance to creep, a broader range of deflection temperatures, and their com~ustion can produce hydrofluoric acid (in the presence of water), which is undesirable in a central office where hundreds of protectors might operate simultaneously, and in subscriber's 15 premi ses .
An advantage of the "planar" or "laminar form of protector disclosed herein, i.e. wherein the protection devices and contacts are assembled onto top and side faces of the support member, is that it facili~ates automatic 20 manufacture. It is anticipated that this wi l l lead to cost savings compared to known protectors which employ coaxial gas tubes, heat coils, solder discs, and so on. Placing the shunt away from the protection devices (SSOVP) enhances the life expectancy of the device since it avoids early tripping of the ~5 protector on low level AC faults that normally can be handled by the SSOVP device. This is in contrast to certain gas tube devices which have a solder pellet mounted directly to the gas tube, and the gas tube device disclosed in the afore-mentioned 206664~ 30 U.~. paten~: speclfication number 4,212,047 which has a fusible plastics sleeve mounted directly upon the gas tube.
The use of a plast7cs film which ruptures to allow short-circuiting of the protectior devices advantageously 5 reduces the size of the protector and permlts an epitaxial form of construction with a general~ly planar cor'tact plate assembl y on one face of a support member .
A disadvantage of protectors employing gas tubes is that the gas tubes are relatively bulky and assembly of the 10 various components is relatlvely complicated and hence relatively costly. The sizQ of the protector may be reduced by using soiid-state devices instead of gas tubes. Such a solid state protector is ~disclosed in U.S. patent number 4,796,150 by Dickey et al, issued 8anuary 3, 1989, to which 15 the reader is directed for reference. Dickey et al disclose protector having a plurality of disc-shaped solid state protection devices located in recesses in opposite sides of a support member and contacting a central ground plane. These devices are secured to the support member by means of U-shaped 2~ spring clips which also provide a path to ground for the surges. Although the individual surge-prctection devices are rel ati vel y smal l, the arrangement i s sti l l rel ati vel y bul ky and compl Icated to assemble.
In preferred embodiments of each aspect of the 25 invention the overvoltage prote-ction device is a solid-state device. It will be appreciated, however, that an alternative protection device, such as a gas tube, could be used.
Mounting the resi~tance eleme~ and circuit elements on a substrate provides a more robust, -hermally efficient and WO 91/0~387 PCT/CA90/00336 ~ 31 ~66~48 reliable protector since it avoids having to solder the resistance element directly to the interconnection means.
Since the snea~; currents are relatively small, it is preferable to maintain a relative7y large separation of 5 the first and second contacts so as to reduce heat absorption.
At the same time, however, it is desirable to melt only a relatively small amount of material to cause the contacts to close. The cruciform spacer effects a satisfactory solution to t~1~ D~r~o,~

' .

Claims (48)

1. A protector arrangement for protecting telephone equipment against excessive voltages, comprising:
a support member (18;218) a protection device (42;236) supported by said support member (18;218);
electrode means (32,34;244,246) for coupling said protection device (42;236) to the equipment to be protected;
mutually proximal first and second contacts (40,74';254,318) biased one toward the other but maintained apart by spacer means (60;322) of thermoplastics material preventing electrical connection between said first contact and said second contact;
interconnecting means (26;240) connecting one terminal (42B) of said protection device (42;236) to said electrode means (32,34;244,246) and to said first contact (40;254);
a contact member (62;312,290) connecting said second contact to a second terminal (42A) of said protection device (42;236) and comprising a ground contact (90;296) for connecting to a ground electrode;
the arrangement being such that excessive heating of the protection device causes the spacer means to melt and permit electrical connection between said first contact and said second contact, characterized in that said first and second contacts and the spacer means therebetween are spaced from said protection device, said interconnecting means providing a heat transfer path for conducting between said spacer means and said protection device the heat required to melt the spacer.

2. A protector arrangement as claimed in claim 1, characterized in that the support member (18;218) supports a second protection device (58;234) and further comprises second electrode means (52,54;288,286) for coupling said second protection device (58;234) to the equipment to be protected, mutually proximal third and fourth contacts (46,72';276,316), the four contacts being spaced from both protection devices (42,58;236,234), said third and fourth contacts being biased one toward the other but maintained apart by spacer means (60;320) of thermoplastics material preventing electrical connection therebetween, second interconnecting means (44;252) connecting one terminal of said second protection device (58;234) to said second electrode means (52, 54) and to said third contact (46;276), said contact member (62;312,290) connecting said fourth contact to a second terminal of said second protection device (58;234), the arrangement being such that excessive heating of the second protection device causes the spacer means to melt and permit electrical connection between said third and fourth contacts, the second interconnecting means providing a heat transfer path for conducting between said spacer means and said second protection device heat required to melt the spacer.

3. A protector arrangement as claimed in claim 1, characterized in that the contact member (62), protection device (42,58) and interconnecting means (26,44), are housed in a housing (10) having at least one aperture (94) in a side juxtaposed to said support member (18), said ground contact (90) being resiliently-biased to project through said aperture.

4. A protector arrangement as claimed in claim 1, characterized in that the interconnecting means (26) extends along one side of the support member (18) to connect to said electrode means (30).

5. A protector arrangement as claimed in claim 2, characterized in that the first and second interconnecting means (26) extend along opposite sides of the support member.

6. A protector arrangement as claimed in claim 1, characterized in that said protection device (42) is located in a recess (20) in said support member (18) and said contact member (62) extends across the mouth of said recess to contact said protection device (42).

7. A protector arrangement as claimed in claim 2, characterized in that said second overvoltage protection device (58) is located in a second recess (22) in said support member (18) and said contact member (62) extends across the mouth of said second recess to contact said second overvoltage protection device.

8. A protector arrangement as claimed in any preceding claim, characterized in that said contact member (62) has slits defining a resilient longitudinally extending limb that is biased away from said support member to serve as said ground contact (90).

9. A protector arrangement as claimed in claim 1, characterized in that said contact member (62) has a medial portion (64) formed as a spring (66, 68), the second contact comprising a marginal portion of said contact member urged towards said first c3ontact by said spring.

10. A protector arrangement as claimed in claim 2, characterized in that said contact member (62) has a medial portion (64) formed as a first spring (66) and a second spring (68), the second contact comprising a marginal portion of said contact member urged towards said first contact by said first spring, and said fourth contact comprises an opposite marginal portion of said contact member urged towards said third contact by said second spring.

11. A protector arrangement as claimed in claim 9 or 10, characterized in that the each said spring (66,68) is substantially semi-cylindrical with its cylindrical axis extending longitudinally of said contact member (62).

12. A protector arrangement as claimed in claim 11, characterized in that said contact member (62) is made of resilient material, and the protector arrangement further comprises fastening means (84) for bearing against said medial portion to urge said marginal portion of said contact member towards said support member.

13. A protector arrangement as claimed in claim 8, characterized in that said spacer means (60) comprises high density, high molecular weight polyolefin.

14. A protector arrangement as claimed in claim 8, characterized in that said spacer means (60) comprises polyethylene having a molecular weight of at least 250,000.

15. A protector arrangement as claimed in claim 14, characterized in that said spacer means (60) comprises polyethylene having a molecular weight in the range 250,000 to 500,000.

16. A protector arrangement as claimed in claim 8, characterized in that said spacer means (60) comprises polyethylene having a specific gravity of at least 0.941.

17. A protector arrangement as claimed in claim 16, characterized in that said spacer means (60) comprises polyethylene having a specific gravity in the range 0.941 to 0.965.

18. A protector arrangement as claimed in claim 13, characterized in that said spacer means (60) comprises polyethylene.

19. A protector arrangement as claimed in claim 1, characterized in that said spacer means (60) comprises a film.

20. A protector arrangement as claimed in claim 1, characterized in that said spacer means (320,322) comprises a limb (324,326) and at least one lateral projection (328,329,330,331), the projection abutting a heat-conductive element (333,335,336,338) for transmitting heat from the protection device (234,236), one of said first and second contacts acting against the limb to urge it towards the heat-conductive element, the arrangement being such that said excessive heating melts the spacer at the junction between the lateral projection and the limb permitting the limb to displace until the first and second contacts make contact.

21. A protector arrangement as claimed in claim 1, further characterized by overcurrent protection means comprising a resistance element (116) connected to said electrode means (30) so as to be in series with a line to be protected, such that heating of said resistance element by excessive current therethrough will cause said spacer means (60) to melt.

22. A protector arrangement as claimed in claim 21, characterized in that said resistance element (116) is substantially planar and disposed in a recess (118) in said support member (18).

23. A protector arrangement as claimed in claim 22, characterized in that said resistance element (116) is a ceramic chip resistor.

24. A protector arrangement, for protecting equipment against excessive voltages and excessive currents, comprising:-at least one overvoltage protection device (42;234,236);
a pair of electrodes (32A,34A;244,246,286,288) for connecting the overvoltage protection device to equipment to be protected;
interconnecting means (120,122;238,240,250,252) connecting said pair of electrodes to one terminal of said protection device;
a contact member for connecting a second terminal of said overvoltage protection device (42) to a ground electrode of the equipment;
first and second contacts (40,74';316,254,276,318) connected to respective ones of terminals of the protection device;
said first and second contacts being biased one toward the other;
thermoplastics spacer means (60,320,322) maintaining separation of said first and second contacts; and a resistance element (116;260,270) connected to said interconnecting means (26,44;238,240,252,284) and in series between one (32A;238,284) of said electrodes and said one terminal (42A) of said overvoltage protection device (42);
means (24;262,272,333,335,336,338) serving to conduct heat from both said resistance element and said overvoltage protection device to said spacer means;
the arrangement being such that melting of said spacer means by heat from either one of said protection device and said resistance element permits electrical connection between said first and second contacts.

25. A protector arrangement as claimed in claim 24, characterized in that said spacer (320,322) comprises a limb (324,326) and at least one lateral projection (328,329,330,331), the projection abutting a heat-conductive element for transmitting heat from the resistance element, one of the pair of contacts acting against the limb to urge it towards the heat-conductive element, the arrangement being such that heat generated by an excessive current melts the spacer at the junction between the lateral projection and the limb and the limb is displaced until the contacts make contact.

26. A protector arrangement as claimed in claim 24, characterized in that said resistance element (116) is substantially planar and disposed in a recess (118) in said support member (18).

27. A protector arrangement as claimed in claim 24, characterized in that said resistance element (116) is a ceramic chip resistor.

28. A protector arrangement as claimed in claim 2, characterized by overcurrent protection means comprising resistance elements (116) each connected to a respective one of said first and second electrode means so as to be in series with a line to be protected, there being a heat transmissive path between each resistance element and a respective one of the spacer means, such that heating of a said resistance element by excessive current therethrough will cause said melting of said spacer means.

29. A protector arrangement as claimed in claim 1, characterized in that said overvoltage protection device (42) is a solid-state protector.

30. A protector arrangement as claimed in claim 28, characterized in that each said overvoltage protection device (42) is a solid-state protector.

31. A protector arrangement for protecting against excessive currents in telecommunications equipment, comprising a resistance element (260,270), electrodes (244,246,286,288) for connecting the resistance element in series with a line to the equipment which is to be protected, a contact member (290) for connecting to a ground electrode when the protector arrangement is in use, a pair of mutually proximal contacts (316,276;318,254) connected one to the contact member and the other to one of the electrodes, said contacts being biased one towards the other, a spacer (320,322) of insulating material preventing electrical contact between said contacts, said spacer comprising a limb (324,326) and at least one lateral projection (328,329,330,331), the projection abutting a heat-conductive element (333,335,336,338) connected to the resistance element, one of the pair of contacts acting against the limb to urge it towards the heat-conductive element, the arrangement being such that heat generated by an excessive current in the resistance element melts the spacer at the junction between the lateral projection and the limb and the limb is displaced until the contacts make contact.

32. A protector arrangement as claimed in claim 31, characterized in that the resistance element (260,270) is mounted upon a printed circuit board (258).

33. A protector arrangement as claimed in claim 32, characterized in that said resistance element is connected to said electrodes by circuit elements (262, 272) printed on said printed circuit board.

34. A protector arrangement as claimed in claim 33, characterized in that at least one of said circuit elements is circuitous and dimensioned to provide a desired thermal impedance between said resistance element and said spacer.

35. A protector arrangement as claimed in claim 31, characterized in that said spacer (320, 322) is mounted upon a support having a hole (332,334), said heat-conductive element being disposed adjacent said hole and said limb being aligned with said hole, said projection being supported at the periphery of the hole, such that melting or at least part of the spacer in the vicinity of the junction between the arms and the limb allows the limb to enter the hole.

36. A protector arrangement as claimed in claim 35, characterized in that the resistance element (260,270) is mounted upon a printed circuit board.

37. A protector arrangement as claimed in claim 36, characterized in that said interconnecting means comprise circuit elements (262,272) printed on said printed circuit board.

38. A protector arrangement as claimed in claim 37, characterized in that said circuit elements are circuitous and dimensioned to provide a predetermined thermal impedance between said resistance element and said interconnecting member.

39. A protector arrangement as claimed in claim 31, comprising a second resistance element, connected to electrodes for connection in series with a second line to equipment to be protected, and a thermal barrier (348) between the first resistance element and the second resistance element.

40. A protector arrangement as claimed in claim 39, characterized in that said second resistance element is connected to a second pair of contacts, such contacts being maintained apart by a second insulating spacer having a limb and a second projection projecting laterally from the limb, said projection being supported by a second heat-conductive element, the second pair of contacts being urged one towards the other by one of the second pair of contacts, the arrangement being such that excessive current in said second resistance element effects melting of at least part of the second spacer in the vicinity of the junction between the projection and the limb allowing the limb to displace until the contacts meet.

41. A protector arrangement as claimed in claim 31, characterized in that said resistance element (116) is a ceramic chip resistor.

42. A protector arrangement for protecting telephone equipment against excessive voltages comprising:
a support member (218);
an overvoltage protection device (236) supported by said support member;
electrode means (244,246) for coupling said protection device to the equipment to be protected;
interconnecting means (240,238) connecting one terminal of said protection device to said electrode means and having a first contact (254);
a contact member (290,312) comprising a ground contact (296) for contacting a ground electrode (310) extending adjacent said protector arrangement when the protector arrangement is installed in said equipment and a second contact (318) juxtaposed to said first contact, said first contact and said second contact being biased one toward the other;

a spacer of thermoplastics material (322) separating said first contact and said second contact, said spacer comprising a limb (326) and at least one lateral projection (330,331), the projection abutting a heat-conductive element (335) for transmitting heat from the protection device, one of said first and second contacts acting against the limb to urge it towards the heat-conductive element, the arrangement being such that said excessive heating melts the spacer at the junction between the lateral projection and the limb permitting the limb to displace until the first and second contacts make contact.

43. A protector arrangement, for protecting equipment against excessive voltages and excessive currents, comprising:-at least one overvoltage protection device (236);
a pair of electrodes (244,246) for connecting the overvoltage protection device to equipment to be protected;
interconnecting means (238, 240) connecting said pair of electrodes to one terminal of said protection device;
a contact member (290,312) for connecting a second terminal of said overvoltage protection device (236) to a ground electrode (310) of the equipment;
first and second contacts (254,318) connected to respective ones of terminals of the protection device, said first and second contacts being biased one toward the other;
thermoplastics spacer means (322) maintaining separation of said first and second contacts; and a resistance element (260) connected to said interconnecting means and in series between one (244) of said electrodes and said one terminal of said overvoltage protection device (236);
the interconnecting means serving to conduct heat from said resistance element to said spacer means;
the arrangement being such that melting of said spacer means permits electrical connection between said first and second contacts, the resistance element and the protection device being both coupled thermally to the spacer, the coupling between the protection device and the spacer having a greater thermal impedance than the coupling between the resistance element and the spacer.

44. A protector arrangement as claimed in claim 43, characterized in that the interconnecting means (262) between the protection device and the spacer is longer than that between the spacer and the resistance element.

45. A protector arrangement as claimed in claim 43, characterized in that the interconnecting means (262) between the protection device and the spacer has a lesser cross-section than that between the spacer and the resistance element.

46. A protector arrangement for protecting telephone equipment against excessive voltages, comprising:
a support member (18) a pair of protection devices (42) supported by said support member (18);
electrode means (32, 34) for coupling said protection devices (42) to the equipment to be protected;
mutually proximal first and second contacts (40,74') biased one toward the other but maintained apart by spacer means (60;320,322) of thermoplastics material preventing electrical connection between said first contact and said second contact;
mutually proximal third and fourth contacts (40,74') biased one toward the other but maintained apart by spacer means (60;320,322) of thermoplastics material preventing electrical connection therebetween;
interconnecting means (26) connecting one terminal (42B) of each of said protection devices (42) to said electrode means (32, 34) and to a respective one of said first contact (40) and said third contact;
a contact member (62) connecting a second terminal (42) of each protection device to a respective one of said second contact and said fourth contact and comprising a ground contact (90) for connecting to a ground electrode (114);
the arrangement being such that excessive heating of the protection device causes the spacer means to melt and permit electrical connection between said first contact and said second contact, characterized in that the pair of protection devices are located in corresponding recesses in a face of the support member, said contact member (62) extends across the mouths of said recesses to contact said protection devices (42), and said interconnecting means (44) extends along a face of the support member (18) adjacent to the first-mentioned face.

47. A protector arrangement as claimed in claim 46, characterized in that the interconnecting means comprise first and second interconnecting means (26) extending along opposite faces of the support member.

48. A protector arrangement as claimed in claim 1, characterized in that the contact member (62), protection device (42,58) and interconnecting means (26,44), are housed in a housing (10) having at least one aperture (94) in a side juxtaposed to said support member (18), said ground contact (90) being resiliently-biased to project through said aperture.