Improvements in or relating to Metallic Junction Boxes for Concentric Electric Conductors and in the Mode of Connecting Conductors therein.
Year: 1893

page_text: .Date of Application, 28th Jan., 1893
Complete Specification Left; 28th Oct., 1893-Accepted, 2nd Dec., 1893
PROVISIONAL SPECIFICATION.
Improvements in or relating to Metallic Junction Boxes for
Concentric Electric Conductors and in the Mode of Connecting
Conductors therein.
We, HENRY ALexander Mavor, William Arthur Coulson and SAM
MAVOR of the Firm of Mavor & Coulson, Electrical Engineers, of 56 George
Square Glasgow in the County of Lanark, and WILLIAM BROOKS SAYERS
Electrical Engineer of Glenwood Bearsden in the County of Dumbartonshire, do
5 hereby declare the nature of this invention to be as follows:-
This invention has reference to metallic junction boxes or cases for concentrio
electric conductors and to a mode of making connections to such conductors or of
taking off branches from the same for which Letters Patent were granted to us
dated 6th October 1891, No. 16,958 and has for its object to provide improved
means whereby the said invention can be applied to concentric conductors of the
type in which the insulated central conductor is enveloped by a second insulated
conductor of tubular form and more particularly when the insulated conductor so
formed is further enclosed in a metallio sheathing or armouring. The principle
upon which the safety of the concentric system of wiring for electric lighting or
of concentric conductors for electric distribution and supply is based, is that one
conductor which may be called the supply, is completely enveloped by a metallic
sheathing which forms the other conductor or return. Our invention for which
Letters Patent No. 16,958/91 were granted, applies principally to cases where the
metallic envelope constituting the roturn conductor is earthed or not specially
O insulated and which might or might not form at the same time protection against
mechanical injury and the intrusion of moisture. The object of the present inven-
tion is to provide improved moans whereby our invention above referred to may be
used when the metallic envelope forming the return conductor is insulated and
more particularly when the supply and return conductors as described are again
3 enveloped in a metallic sheathing or armouring to give mechanical protection to
exclude moisture and for convenience in making connections. For this purpose
the outer metallic sheathing and lead covering either one or both according to the
type of cable or conductor upon which the connection is to be made and the
succeeding layers of which the cable is composed are cut away in steps at
O the point where connection has to be made leaving suitable lengths of the layers
of insulating, and conducting material projecting. A contact button is then
soldered upon the central conductor; next a metallic oup or thimble having a
central hole co-axial with the rim of such diameter as to pass small end of
connecting plug hereinafter described and one or more notches or side openings
according to the number of conductors passing into or out of the box of suitablo
shape and of depth to allow the insulated central core of the conductor to pass into
the interior of said cup is placed upon the cable so that the contact button is
opposite the co-axial hole in the cup or thimble. The diameter of the cup is such
as to leave sufficient longth of the insulated covering of the central conductor
between the contact button and the rim of the cup to avoid risk of connection or
short circuit between the two. The outer insulated conductor when composed of
stranded wire is preferably out in the centre and the wire straightened out and
bent back over the insulating covering exterior to them for convenience in cop-
pecting to the insulated cup hereinafter described. The wires of the outer
5 insulated conductor are then arranged around the outside of the cup or thimblo
preferably in a symmetrical fashion and soldered thereto: or the edges of the
notches or openings in the side of the cup or thimble may be formed with projecting
lips to. fit, around the outer insulated conductor the lips then being soldered to the

page_text: same. In this latter case the outer insulated conductor would be cut away in tho
centre leaving part projecting beyond its insulating covering instead of being
parted in the middle and bont back as described when the conductor is to be
wrapped rotind the outside of thimble. An insulating disc of vulcanite, hard wood
or other suitable insulating material is next fitted into the end of thimble against
the back of the contact button, and the end of the thimble is then closed by a
metal cap preferably soldered in. The thimble now forms part of the outer
insulated conductor and encloses the contact button having only a hole opposite
said contact button for the insertion of the contact plug hereinafter described.
The cable is next laid into a junction box or case made according to our herein-
before referred to Patent No. 16,958/91 care being taken that the hole in the cup
is placed opposite the screwed hole for receiving the fitting or brauch in the
external case or junction box the ends of the sheathing or other covering of the
cable are thon sealed into the pockets formed in the case in the manner described
in the before mentioned Patent No. 16,958/91 and the central cavity containing the
parts described is closed first with an insulating disc and next with a metal cover
sealed on by soldering. The connection to the parts enclosed in the junction box
is made by means of a plug consisting of a cylindrical holder or part made of
insulating material mounted in the end of a metal tube which is screwed externally
to fit the junction box. The insulating holder has a projection co-axial with
screwed tube of suitable length and diameter on the end of which is a contact
button which is connected to ono wire of the fitting or other apparatus to be
connected. The connection to the other wire of the fitting or other apparatus is
made through a helical spring attached to the end of the other conductor and
preferably abutting against a shoulder formed on the insulating holder. The length
of the projecting insulating part and the position of the shoulder are such that
when the plug is screwed into position in the junction box, the helical spring first
makes contact with the end of the thimble and when compressed sufficiently to
make a proper contact the contact button on the end of the holder comes into
contact with the button which is fixed to the inner or supply conductor. Thus
connection is established with both the inner and outer conductors and the opening
in junction box is closed by the screw plug,
The invention may be applied to the making of junctions between cables or con-
ductors without the use of the screw plug and when so used the co-axial hole in
the insulated cup or thimble is not required; the number of notches or openings
around the rim as also the number of pockets in the external case or junction
box corresponding with the number of conductors entering and leaving the junction
box.
1
HENRY A. MAVOR.
W. ARTHUR COULSON.
SAM MAVOR.
W. B. SAYERS.
COMPLETE SPECIFICATION.
Improvements in or relating to Metallic Junction Boxes for 46
Concentric Electric Conductors and in the Mode of Connecting
Conductors therein.
B
HENRY ALEXANDER MAVOR, WILLIAM ARTHUR Coulson and Sam Mavor,
of the Firm of Mavor and Coulson, Electrical Engineers, 67 West Nile Street,
late of 56 George Square, Glasgow, in the County of Lanark, and WILLIAM 60
BROOKS SAYERS of Glenwood, Bearsden, near Glasgow, in the County of
Dumbarton, do hereby declare the nature of this invention and in what manner
the same is to be performed, to be particularly described and ascertained in and
by the following statement
This invention has reference to metallic junction boxes or cases for concentrio of

page_text: electric conductors, an to a mode of making connections to such conductors, or
of taking off branches from the same for which Letters Patent were granted to us
dated the sixth day of October Eighteen hundred and ninety one- -No. 16,958 and
has for its object to provide improved moans whereby the said invention can be
applied to concentric conductors of the type in which the insulated central
conductor is enveloped by a second insulated conductor of tubular form and more
particularly when the insulated conductor so formed is further enclosed in a metallio
sheathing or armouring.
The principle upon which the safety of the concentric system of wiring for
electric lighting, or of concentric conductors for electric distribution and supply is
based, is that one conductor, which may be called the supply, is completely
enveloped by a metallic sheathing_which forms the other conductor or return.
Our invention for which Letters Patent No. 16,058/91, were granted, applies
principally to cases where the metallic envelopo constituting the return conductor
was earthed or not specially insulated, and which might or might not form at the
same time protection against mechanical injury, and the intrusion of moisture.
The object of the present invention is to provide improved moans whereby our
invention above referred to, may be used when the metallic envelope forming the
return conductor is insulated, and more particularly when the supply and return
conductor as described are again enveloped in a metallic sheathing or armouring
to give mechanical protection to excludo moisture and for convenience in making
connections.
For this purpose the outer metallic sheathing and lead covering either one or
both according to the type of cable or conductor upon which the connection is to
be made and the succeeding layers of which the cable is composed are cut away
in steps at the point where connection is to be made leaving suitable lengths of the
layers of insulating and conducting material projecting. A contact button is then
soldered upon the central conductor, next a metallic cup or thimble having a
central hole co-axial with the rim of such diameter as to pass the small end of
connecting plug heroinafter described and one or more notches or side openings
according to the number of conductors passing into or out of the box of initable
shape and of depth to allow the insulated central core of the conductor to pass into
the interior of said cup is placed upon the cable so that the contact button is
opposite the co-axial hole in the cup or thimble.
The diameter of the cup is such as to leave a sufficient length of the insulating
covering of the central conductor between the contact button and the rim of the
cup to avoid risk of connection or short circuit between the two. The outer
insulated conductor when composed of stranded wires is preferably out in the centre
and the wires straightened out and bent back over the insulating covering exterior
to them for convenience in connecting to the insulated cup hereinafter described.
The wires of the outer insulated conductor are then arranged around the outside of
the cup or thimble proferably in a symmetrical fashion and soldered thereto, or the
edges of the notches or openings in the side of the cup or thimble may be formed
with projecting lips to fit around the onter insulated conductor the lips then being
Boldered to the same. In this latter case the outer insulated conductor would be
cut away in the centre leaving part projecting boyond its insulating covering
instead of being parted in the middle and bent back as described when the
conductor is wrapped round the outside of thimble. An insulating disc of vulcanite,
hardwood, or other suitable insulating material is next fitted into the end of the
thimble against the back of the contact button, and the end of the thimble is then
closed by a metal cap preferably soldered in. The thimble now forms part of the
outer insulated conductor and encloses the end of the contact button having only
a hole opposite said contact button for the insertion of the contact plug bereinafter
described. The cablo is next laid into a junction box or case made according to
our berein-before referred to Patent No. 16958/91, care being taken that the hole
in the cup is placed opposite the screwed hole for receiving the fitting or branch in
the external case or junction box the ends of the sheathing or other covering of

page_text: the cable are then sealed into the pockets formed in the case in the manner
described in the before mentioned Patent No. 16958/91, and the central cavity
containing the parts described is closed first with an insulating disc, and next with
a metal cover sealed on by soldering.
The connection to the parts enclosed in the junction box is made by means of a
plug, consisting of a cylindrical holder or part made of insulating material mounted in
the end of a metal tube which is screwed externally to fit the junction box.
The insulating holder has a projection co-axial with the screwed tube of suitable
length and diameter on the end of which is a contact button which is connected to
one wire of the fitting or other apparatus to be connected. The connection to the
other wire of the fitting or other apparatus is made through a helical spring
attached to the end of the conductor, and preferably abutting against a shoulder
formed on the insulating holder. The length of the projecting insulating part,
and the position of the shoulder are such that when the plug is screwed into
position in the junction box, the helical spring first makes contact with the end of
the thimble, and when compressed sufficiently to make a proper contact the contact
button on the end of the holder comes into contact with the button which is fixed to
the inner or supply conductor. Thus connection is established with both the inner
and outer conductors and the opening in the junction box is closed by the screw
plug.
The invention may be applied to the making of junctions between cables or
conductors without the use of the screw plug and when so used the co-axial hole in
the insulated cup or thimble is not required; the number of notches or openings
around the rim as also the number of pockets in the external case or junction
box corresponding with the number of conductors entering or.leaving the junction
box.
Referring to the attached drawings
Fig. 1 is a vertical section and Fig. 2. a horizontal section on line 2. y. of a
junction box made according to our invention and applied to lead covered and
armoured cable.
In both figures A is the cable in which al is the central insulated con-
ductor 61. the insulating material between it and outer insulated conductor.
62, 63, is the lead sheathing, 64 a serving of jute or equivalent material, and
65 the external armouring. The various layors of the cable are cut away suc-
cessively in steps, as shewn in Fig. 1. so as to exposo suitable portions of them for
making the several connections as described. Ċ is the contact button which is
soldered to the central insulated conductor al; D is the metallio thimble having
a hole d 1 co-axial with the rim, through which passes the insulating stem of the
contact plug F. 2, d2, are the notches or sido openings which are formed with
U shaped lips so as to fit around the under side of the outer insulated conductor a 2,
and to which they are sweated or soldered so as to make a good electrical con-
nection; d3, (Fig. 1.) is the insulating disc of mica, vulcanite, hardwood, or other
Fuitable material and №4 is the metal cap which is preferably soldored into the
insulated cup or thimble D. (Fig. 1 & 2.). E is the junction box made according
to our Specification No. 16958/91 having the pockets e 1, e1, el, into which the
molten solder or fusible metal is poured; also the insulating disc 2 and the cover
or dish € 3, which are both fitted and the dish soldered in, all in accordance with
our aforementioned Specification No. 16958/91. F. (Fig. 1.) is a section of a
plunger for making connection to the insulated conductors within the junction box,
in which 1 is the cylindrical holder of insulating material, such as hardwood,
porcelain, or other suitable material, 2 the metal tube or thimble into which it is
fixed and which is screwed externally to fit the screwed oponing e4 in the junction
box E. ₤3 is the contact button which is connected to one wire of the fitting or
other apparatus for which the supply is tapped, and which is mounted upon the
co-axial projection on tho insulating holder 1. This co-axial projection passes
through the hole d1 in the insulated thimble D aud makes connection with the
contact button C. ƒ4 (Fig. 1.) is the helical spring which makes contact against

page_text: the shoulder formed by the edge of the hole d 1 in the insulated thimble D. and
the other end of which rests against the shoulder on the insulating holder f1, and is
connected to the other wire of the fitting or other apparatus.for which the supply
is tapped. When the invention is used to form a connection between two or more
cables and it is not desired at the same time to tap the supply for a fitting or other
apparatus by means of the plug F. the central conductors are united to each other
by soldering to the contact button Cand the junction box is made without any
screwed opening as indicated by dotted lines Fig. 1. or tho screwed opening may be
closed by a metallic plug. Figs. 3, 4, 5, and 6 represent respectively one way, two
way, three way, and four way junction boxes according to our invention. Our
invention is applicable to concentric conductors having two or more conductors
insulated from oue another either armoured metallically covered or unarmoured.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner it is to be performed we declare that what we
claim is :-
1. The method of making junctions in or between concentric electric cables
having both conductors insulated and at the same time tapping the supply for a
fitting or other apparatus substantially in the manner, and for the purpose herein
set forth with reference to Figs. 1, 2, 3, 4, 5 & 6 of the accompanying drawings.
2. The method of making junctions in or between concentric electric cables
having two or more insulated concentric conductors substantially in the manner and
for the purpose herein set forth with reference to Figs. 1, 2, 3, 4, 5 and 6, of tho
accompanying drawings.
Dated this Twenty-seventh day of October 1893.
HENRY A. MAVOR.
W. ARTHUR COULSON.
SAM MAVOR.
W. B. SAYERS.