Overvoltage protector unit for well constructions

Overvoltage protector unit for use in a well in which an overvoltage protection device is mounted in a grounding housing and electrically separates a conductor pin in the housing from the housing during normal voltage conditions. The conductor pin is mounted within a flame resistant resilient elastomeric dielectric support which also electrically isolates it from the housing. The support cushions the pin before installation of the unit and the unit is unlikely to suffer damage during storage or transit upon the protection device failing, the resilient support flexes to enable line to ground contact to be established.

This invention relates to overvoltage protector units for well 
constructions. 
In the telecommunications industry, overvoltage protector units are known 
to protect telecommunications equipment within customer's premises from 
damage such as could be caused by overvoltage conditions. These conditions 
may suddenly occur. For instance, an overvoltage condition may be as a 
result of a lightning strike to an outside line. Some overload protectors 
are of a design suitable for use in central offices in which an overload 
protector is provided in each line. Each protector normally includes two 
overvoltage protection unit devices and two overcurrent protection 
devices, the protection devices providing individual overvoltage and 
overcurrent protection for each tip and each ring line. 
In other constructions, overvoltage protection units are designed for 
fitting into wells which are formed by holes provided in a dielectric 
housing into which such a unit is fitted at one end of the well. A 
conductor line extends across the other end of the well and contact is 
made to the conductor line when the protection unit is disposed within the 
well. These constructions are such that the protector units are 
manufactured separately from the dielectric housings, the housings being 
attached permanently to walls of customer's premises and providing with 
the units the complete overvoltage protector. The protector units are 
manufactured separately in large quantities to be used, not only upon new 
facilities, but also as replacements for overvoltage protector units which 
have been subjected to overvoltage conditions and have failed. It is not 
uncommon therefore for large quantities of such protector units to be 
stored in containers or to be carried by maintenance and installation 
staff to various sites where replacement of protector units is required. 
As a result, such protector units should be substantially robust to 
protect them from damage either during storage or in transit. 
However, the structure of conventional protector units is such that they 
may be vulnerable to damage before they have actually been installed and 
such damage may render them completely unworkable or may make them 
function incorrectly after installation. Constructional features which 
render them vulnerable comprises a conductive cup or basket holding within 
it an overvoltage protection device and a conductor pin which is held 
within the cup or basket by a ceramic dielectric so that electrical 
contact with the cup or basket is avoided. The one end of the conductor 
pin extends from an open end of the cup or basket for contact with 
conductor the line upon assembly into a well. The ceramic and the 
conductor pin are held in position by fingers at the open end of the cup 
or basket, the fingers projecting into an annular groove in the ceramic. 
The other end of the conductor is electrically in contact with one side of 
an overvoltage protection device the other side of which is electrically 
connected to a base of the basket and to ground potential. Any sustained 
overvoltage condition results in failure of the overvoltage protection 
device so that grounding of the conductor line takes place through the 
base of the basket with the fingers making contact with the conductor line 
under spring pressure. 
Because of the geometry of the arrangement, it is necessary for the fingers 
to project outwardly beyond an open end of a housing which is used to 
assemble a unit into the dielectric housing. These fingers may become bent 
during handling or storage and such damage may easily result where a large 
number of the protector units are gathered together and are randomly and 
freely movable against each other inside a container. Distortion of one or 
more of the fingers may result in loosening of the ceramic holding the 
conductor pin possibly resulting in axial misalignment of the pin and the 
basket so that inaccurate installation and incorrect operation may occur 
or short may occur upon installation. In addition, the ceramic material 
itself may become cracked or broken if a protector unit is dropped thereby 
affecting the dielectric properties. 
The present invention seeks to provide an overvoltage protector unit which 
will minimize the above problems. 
Accordingly, the present invention provides an overvoltage protector unit 
comprising a housing for assembly into a well, the housing having an open 
end, a conductor and an overvoltage protection means disposed electrically 
in an in-series arrangement located at least partly within the housing 
with a first end of the arrangement electrically connected to the housing 
and electrically isolated from a second end of the arrangement during 
normal operating conditions, and the arrangement is also disposed with the 
second end accessible for the application of an end load in a direction 
into the open end of the housing, the overvoltage protection means being 
operable, in use, to fail upon sustaining certain abnormal voltage 
conditions in a respective signal line, and the conductor mounted within a 
surrounding flame resistant resilient elastomeric dielectric support means 
which is resiliently flexed by the end load upon failure of the 
overvoltage protection means caused by sustained overvoltage conditions so 
as to cause electrical connection between the first and second ends of the 
in-series arrangement. 
With the above structure according to the invention, no finger arrangement 
is required to hold the conductor and the dielectric support means. Also, 
the dielectric support means is a flame resistant resilient elastomeric 
material thereby avoiding problems with the use of a brittle dielectric 
support should the protector unit be mishandled. 
In one preferred construction a cup member is mounted within and is 
electrically connected to the housing. An open end of the cup member faces 
in the same direction as the open end of the housing and the in-series 
arrangement lies within the cup member. In this structure, resilient means 
resists movement of the cup member further into the housing. 
In an alternative preferred construction, no cup member is provided and the 
overvoltage protection means is immovably mounted within the housing. 
In the preferred constructions, it is preferred that the dielectric support 
is held by a friction grip within the cup member or the housing as the 
case may be. Alternatively, the dielectric support means may be disposed 
in position, for instance, by a suitable adhesive which is compatible both 
with the material of the dielectric support means and of the cup member or 
of the housing. 
To locate the dielectric support means correctly within the cup member, it 
is advantageous to provide the cup member and the dielectric support means 
with interengaging axially extending groove and rib means. Preferably, 
this comprises at least three grooves and interengaging ribs spaced apart 
circumferentially of the cup member and dielectric support means so as to 
stabilize the dielectric support means within the cup member. In a 
practical construction, the grooves are formed in the cup member and the 
ribs upon the dielectric support means. 
It is also preferable for the dielectric support means to be prestressed 
within the cup member or within the housing to prevent the conductor from 
moving uncontrollably and minimize the possibility of the conductor 
becoming misaligned relative to the overvoltage protection device should 
the protector unit be mishandled. Prestressing may be provided with parts 
of the dielectric support means adjacent to the cup member or housing 
being held resiliently biassed axially of the conductor beyond a normal 
unstressed position relative to inner parts of the support means. It is 
also preferable for the dielectric support means to have radially inner 
and outer annular walls, the inner wall securely mounting the conductor 
and the outer wall connected by resilient web means to the inner wall. 
With such an arrangement the prestressing of the dielectric support takes 
place about the web means as this allows for axial displacement of the 
outer wall relative to the inner wall. 
Although the overvoltage protection device may comprise carbon or gas tube 
devices, the protector unit according to the invention is particularly 
suitable for use with a protection device which comprises a solid state 
overvoltage protection device. 
The invention also includes an overvoltage protector comprising a 
dielectric body and an overvoltage protector unit, wherein: the dielectric 
body defines a well and has a first conductor means secured to the 
dielectric body and extending into the well at a position spaced from an 
opening to the well; and the overvoltage protector unit comprises a 
housing having an open end, the housing mounted through the opening and 
into the well with the open end of the housing facing towards the first 
conductor means while being electrically isolated from the first conductor 
means, and with the housing electrically connected to a second conductor 
means, a conductor and an overvoltage protection means disposed 
electrically in an in-series arrangement located at least partly within 
the housing with a first end of the arrangement electrically connected to 
the housing and electrically isolated from a second end of the arrangement 
during normal operating conditions, the second end electrically connected 
to the first conductor means, the overvoltage protection means being 
operable, in use, to fail upon sustaining certain abnormal voltage 
differential conditions between the first and second conductor means, and 
the conductor mounted within a surrounding flame resistant resilient 
elastomeric dielectric support means; the first conductor means applying 
an end load to the second end of the in-series arrangement whereby upon 
failure of the protection means, the second end of the in-series 
arrangement is caused to move towards the first end during resilient 
flexing of the dielectric support means to provide an electrical 
connection between the first and second ends.

In a first embodiment, as shown in FIG. 1, an overvoltage protector unit 10 
comprises a drawn metal housing 12 having a closed end 14 at which is 
provided an hexagonal end region 16 (see FIG. 2) for engagement by a 
wrench for mounting the housing within a well. For this purpose the 
housing is formed with a rolled thread 18, and a flange 20 for seating 
against a dielectric member (to be described) is disposed between the end 
region 16 and the rolled thread 18. 
Within the housing 12 is disposed a resilient means in the form of a 
compression spring 22 which is engaged at one end against the closed end 
14 and has its other end in engagement with a cup member 24 which is 
slidable within a cylindrical skirt 25 of the housing member 12, the 
housing being open at a free end 27 of the skirt. The cup member 24 is of 
substantially cylindrical form shaped from stamped and formed metal strip 
or sheet and has a cylindrical wall 26 one end of which is formed with 
abutment means provided by four circumferentially spaced flanges 28 which 
extend inwardly from the wall 26 towards a common axis of the cup member 
and the protector unit. The spring 22 rests against the flanges 28 as is 
clearly shown in FIG. 1. At its other end, the cup member is open and the 
position of the cup member is such that the open ends of cup member and 
housing 12 face in the same direction from the protector unit with the cup 
member extending slightly outwardly beyond the open end of the housing as 
shown in FIG. 1. 
Within the cup member is disposed an overvoltage protection means which 
comprises a solid state overvoltage protection device 30 of known 
construction. The device 30 is spaced from the abutment means provided by 
the flanges 28 by a solder pellet 32 of the overvoltage protection means, 
the pellet 32 seated against the flanges 28. The solder pellet 32 is of 
doughnut shape and has a central hole 34. 
Within the cup member 24 and below the overvoltage protector device 30 is 
disposed an assembly 36 of a conductor 38 and a dielectric support means 
for the conductor 38. The support means is provided by a molded flame 
resistant resilient elastomeric support capable of withstanding 
temperatures to which it may be raised during passage of an overvoltage 
surge through the conductor 38. In this embodiment the support is an 
olefin based elastomer. 
While the dielectric support 40 may be of a solid molded material, it is in 
this embodiment formed with an inner wall 42 and an outer wall 44 which 
are connected together during molding by a radially extending resiliently 
flexible web 46 of annular configuration. The structure of the dielectric 
support 40 is shown particularly in FIG. 3. 
The conductor 38 comprises a conductive pin with a knurled outer surface 48 
separating an upper small end 50 and a lower enlarged end 52. The 
conductor 38 is mounted within the dielectric support 40 during molding of 
the support so that the inner wall 42 of the support is molded into the 
knurled surface of the conductor thereby securely fixing the conductor 
within the inner wall. 
For location purposes within the cup member 24, interengaging axially 
extending groove and rib means is provided between the cup member and the 
dielectric support. For complete stabilization, the groove and rib means 
requires at least three grooves and interengaging ribs spaced 
circumferentially of the cup member and dielectric support. In this 
embodiment four ribs 54 are molded in equally spaced positions apart 
around the outer wall 44 of the cup member as is shown in FIG. 2, each of 
the ribs extending axially along the outer surface of the outer wall. 
Similarly, the cup member 24 is pressed with four axially and radially 
outwardly extending projections 56 which are also equally spaced around 
the cup member (FIG. 2), these projections forming grooves 58 (FIG. 1) on 
the inside surface of the cup member. 
As shown by FIG. 3, the dielectric support 40 is molded with the web 46 in 
an unstressed condition and lying substantially in radial planes of the 
support. However, upon assembly of the dielectric support into the cup 
member 24 and upon the complete assembly of the protector unit 10, then 
the dielectric support is pressed into the cup member and the conductor 38 
terminates in its axial movement during insertion upon engagement of its 
end 50 with the protection device 30 as shown by FIG. 1. The conductor 38 
and the overvoltage protection means thus form an in-series arrangement in 
which they are connected electrically. The outer wall 44 of the dielectric 
support 40 is pressed further into the cup member 24 so that it moves 
axially beyond a normal unstressed position relative to the inner wall 
whereby the web 46 is in a resiliently flexed and stressed condition. This 
is indicated in FIG. 1 wherein as can be seen, the web 46 in its stressed 
condition is arched slightly upwardly out of the normal planar condition 
shown in FIG. 3. The reason for forcing the inner wall into this position 
within the cup member is to prestress the web 46 and stabilize the inner 
wall and supported conductor 38 within the cup member so as to resist any 
tendency of the conductor and the inner wall to move freely under impact 
loads caused for instance by handling of the protector unit before 
installation. The position of the conductor 38 is thus controlled and 
cannot become misaligned with the protector device 30 before installation 
into a well. 
In the assembled condition, the dielectric support 40 is thus assembled 
into the cup member 24 and is held in position by frictional grip with the 
ribs 54 engaged within the grooves 58. The cup member 54 has a slight 
frictional contact with the housing 12 so as to resist any tendency for 
the cup member to fall completely from the housing. 
In use and to provide an overvoltage protector, as shown by FIG. 4, the 
overvoltage protector unit 10 is inserted into a well 60 formed in a 
molded solid dielectric body 62 secured to the wall of a customer's 
premises. In the assembled condition the exposed larger end 52 of the 
conductor 38 engages a conductor means in the form of a domed region 64 of 
a plate 66 which forms part of the telecommunications line, the domed 
region extending into one end of the well. The overvoltage protector unit 
is inserted from the other end of the well with the screw thread 18 screw 
threadably engaged with a corresponding thread 68 in the hole. During 
insertion of the unit 10 into the well 60, the domed region 64 in engaging 
the conductor 38 holds the conductor in position as the housing is screwed 
downwardly into the well. This causes the domed region 64 to apply an end 
load against the end 52 of the conductor 38 and axially up into the 
housing 12, resulting in movement of the cup member 24 towards the closed 
end 14 of the housing 12 thereby compressing the spring 22 as shown by 
FIG. 4. In this condition, the cup member 24 while being electrically 
connected to housing 12 is isolated from the conductor 66, the free end 27 
spaced from the domed region 64. At the other end, the housing 12 is 
permanently connected to ground by a ground conductor (not shown) clamped 
between an annular ridge 69 of the housing and the flange 20. 
During normal usage, line current passes along the line 66. Upon being 
subjected to a surge in voltage, a sustained overvoltage condition results 
in a breakdown in the overvoltage protection device 30 and the solder 
pellet 32 becomes heated and is melted and is caused to flow partially 
into the aperture 34 under spring pressure. The removal of the pellet 32 
in this fashion results in the spring 22 urging the cup downwardly 
relative to the conductor 38 so that the lower free end 27 of the cup 
member 24 engages the domed end 64 of the line 66. This is the position 
shown in FIG. 5. This movement, as may be seen from a comparison of the 
positions of the web 46 in FIGS. 4 and 5, results in the outer wall 44 
being carried with the cup member axially relative to the inner wall 42 
whereby the web 46 returns towards its initial unstressed condition. 
As may be seen from the above embodiment, the overvoltage protector unit 
having the flame resistant resilient elastomeric dielectric support 
provides a structure which, in a stressed condition within the cup member, 
holds the conductor 38 in stable condition in axial alignment with the 
overvoltage protector device 30 during mishandling before installation of 
the unit into a well. In addition, the support 40 is secured within the 
cup member by frictional grip thereby eliminating the need for weak 
holding structures such as fingers to hold a ceramic support in position 
and which could become broken due to mishandling before insertion into a 
well. 
In a second embodiment as shown in FIG. 6, a structure of protector unit 70 
is similar to that described for the first embodiment and is also shown 
inserted into a well 60 in a solid molded dielectric member 62. In this 
structure, features similar to those described in the first embodiment 
bear similar reference numerals. The unit 70 differs from unit 10 of the 
first embodiment in that it has a dielectric support 72 having an inner 
wall 42 and an outer wall 74 integrally formed together by a web 46 and in 
which the outer wall 74 extends axially towards the closed end 14 beyond 
that of the first embodiment. In the second embodiment, the axial 
extension 76 of the wall 74 is sufficient of the protection device 30. 
This arrangement is used to simplify the alignment of the parts during 
assembly of the protector unit. 
In a third embodiment shown in FIGS. 7 and 8, a protector unit 80 is of 
simpler construction than the units of the first and second embodiments in 
that the unit 80 does not include a resilient means, i.e. a compression 
spring within its structure and no cup member is provided. 
Instead in the unit 80 which bears reference numerals included in the first 
and second embodiment for similar parts, the in-series arrangement of the 
conductor 38 and the overvoltage protection device 30 are disposed with 
the conductor held within the dielectric support 72. As shown, the solder 
pellet 32 contacts the radial wall 82 forming the base of a cup 84 formed 
in the closed end 14 of a housing 86. The dielectric support 72 is 
frictionally held by the inside surface of the partially threaded 
cylindrical wall 88 of the housing. The axial extension 76 of the wall 74 
surrounds the protection device 30 to hold it radially in position and the 
solder pellet which is bonded to the protection device 30 is thereby also 
held radially in position. 
In assembled condition of the unit, the wall 74 is urged axially beyond its 
normal unstressed position relative to the inner wall 42 so as to 
prestress the resiliently flexible web 46 and urge the conductor 38 
towards the closed end 14 of the housing 86 thereby holding the solder 
pellet 32 and protection device 30 axially in position between the radial 
wall 82 of the cup 84 and the small upper end 50 of the conductor. 
The protector unit 80 is incorporated, in use, into a well 90 in a molded 
solid dielectric body 92 as shown in FIGS. 7 and 8. A line conductor 94 
forms a dish 96 at the base of the well, the dish holding one end of a 
compression spring 98 which is compressed through engagement at its other 
end with a disc 100 which is urged downwardly by engagement with the lower 
end 52 of the conductor 38 as the housing 86 is screwed into position 
within the well. 
The spring thus places an end load upon the conductor 38 whereby, upon 
attainment of a sustained overvoltage condition, the overvoltage 
protection device 30 fails resulting in melting of the solder pellet as 
current passes through it and into the housing and the disc 100 is urged 
by the spring 98 upwards into electrical contact with the lower end of the 
housing (FIG. 8). This action results in permanent electrical connection 
between the line conductor 94 and a ground conductor (not shown) held 
between a flange 102 of the housing and the upper end of the dielectric 
body 92. The upward movement of the disc 100 causes the conductor 38 and 
inner wall 42 of the dielectric support also to move upwardly so that the 
web 46 is flexed.