Improvements in Connecting-plugs for Electrical Switch-boards.
Year: 1899

page_text: Date of Application, 1st Nov., 1899-Accepted, 6th Jan., 1900
COMPLETE SPECIFICATION.
Improvements in Connecting-plugs for Electrical Switch-boards.
We, ARTHUR THOMAS MILNOR THOMSON, of No. 51, Beauval Road, East
Dulwich, in the County of Surrey, Electrical Engineer, and PERCY WARNFORD.
DAVIS, of Pomona Buildings, No. 61, Fore Street, in the Administrative County
of London, Gentleman, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement:
-
The present invention relates to improvements in connecting-plugs for electrical
switch-boards.
One of the main objects of it is to prevent the connecting wires carried in the
cord becoming broken, especially at or near the plug, which they frequently do
with the plugs as now constructed owing to the fact that the cord is led into
the extreme end of the plug, so that when the plug is being pushed into the.
jack the cord becomes bent and squeezed up between the end of the plug and the
hand, and it is not infrequent that operators drive the plug in by a blow with the
open hand, which even more suddenly and sharply bends the wires contained
in the cord; moreover when again withdrawing the plug, the cord, which has
been bent to nearly a right-angle in inserting the plug, is now straightened
again by raising it, and indeed the plugs are often pulled out solely by their
cords, and this frequent bending and rebending or straightening of the wires
at one place within the cord, notwithstanding that the latter is specially thickened
at the part handled, that is, near the plug, soon results in the breakage of the
wires, entailing much inconvenience and expense.
We will now proceed to describe my invention in detail, reference being had
to the accompanying sheet of drawings illustrating same, and in which:-
Figure 1 is a longitudinal section of a three-way plug, to which is connected
a two-wire or two-way cord, constructed in accordance with my invention.
Figure 2 is a longitudinal elevation of the tip and sleeve sections combined,
detached from the casing.
Figure 3 is a longitudinal elevation of the tip-section, detached.
Figure 4 is a longitudinal elevation of the combination of sleeve-section and
casing, detached.
Figure 5 is a cross-section of the complete plug, taken on the line 5-5 of
Figure 1.
Figure 6 is a cross-section of the complete plug, taken on the line 66 of
Figure 1.
Figure 7 is a longitudinal elevation of the complete plug and portion of
connecting-cord.
Figure 8 is the indicating disc which may be substituted for a lamp in the
end of the plug.
It must be understood that these drawings of a three-way plug and two-way
cord, are only given by way of example and that the invention may be embodied
in a two-way plug in combination with a three-way cord, and further, that if
necessary, more ways for the electric current may be provided either in the plug
[Price 8d.]

page_text: or the cord or both and a suitable number of contacts provided in the jack
accordingly.
In plugs as hitherto, constructed it has been customary for the cord bearing
the connecting wires to he led in at the extreme rear end of the plug, that is to
say, in alignment with the remainder of the plug. Thus the part of the cord
which enters the plug, under normal conditions is bent in relation to the re-
mainder of the cord which hangs downwards, and when in use the said bend
of the cord necessarily is interposed between the extreme end of the plug and the
hand, with the result above explained. Moreover, it is customary to screw-thread
the internal surface of the ferrule at this end of the plug to afford a grip for the
cord which is simply screwed therein, but as may be easily imagined, the material
of which the cord is composed being soft, the grip of it on the screw-threads
is very feeble and in actual practice it is found to very soon become loose and
limp at the part just outside the plug, thus bending the wires within it to a
curve smaller than is good for them.
Again, no provision has hitherto been made in these plugs whereby a particular
plug can be distinguished at a distance at a glance, when in the jack, from others
surrounding it thus much time is now taken up in tracing the connections or
cords in complicated systems, which in busy exchanges is appreciable.
We have endeavoured to remedy all the above defects and have succeeded in
devising means whereby the connection wires are prevented from becoming
broken and also means whereby any particular plug in use can be instantly dis-
tinguished from others.
According to our invention, in order to prevent the connection-wires becoming
unduly bent and so broken at or near the plug, instead of screwing the cord in
the end of the plug as usual, the casing of the plug is provided with a hole or
lateral passage as shewn at 1 (Figures 1, 4 and 7). This passage is preferably
formed with sloping sides indicated by 2, in order to afford the cord a good
bearing and support it at a fixed angle.
If desired, the passage 1 may be situated at some other part of the casing for
example nearer the middle, but it is advantageous to have it as near to the rear
end of the plug as possible for the reason that the connection cord when the plug
is in a jack is then more out of the way of other plugs in adjacent jacks; the
jacks on a switch board being sometimes required to be rather close together.
Further, the said passages may be extended outside the plug in the form of
a projecting tube if desired but in practice a mere oblique hole such as shewn is
found to answer the purpose well and is preferable.
Should a projecting tube be used it may be made of either a rigid material
such as metal or a flexible one such as india-rubber; or since its object would
be simply to afford a longer bearing and consequently a better support for the
cord, a mere helix of wire may be fastened to the casing and extend a short way
along the cord.
In order that the connection-cord may be readily inserted in the plug and
firmly secured in position the end of the plug is preferably made removeable and
as a matter of fact half the hole 1 is formed in the removable end 3-which latter
in the drawings (see Figures 1, and 7) is in the form of a socket to contain a
lamp 4 and half in the end of the casing, so that on sliding the removable socket 3
on to the end of the casing 5, up to the annular shoulder 6 formed on the pasing.
the cord becomes gripped between the two halves of the hole 1: the end piece
being in place it is secured by any suitable means such for example as a screw 7
tapped through it and into the casing 5.
By the above arrangement it will be seen that the cord cannot become unduly
bent by being squeezed between the hand and the end of the plug because the
cord enters the plug laterally and the fact of the cord being clamped in position
by the removable end piece 3 as above stated, ensures the cord being fixed firmly
at a certain angle and so prevents the wires being bent to-and-fro at each insertion
and withdrawal of the plug from the jack. Moreover, the removable piece 3

page_text: provides a projection to catch hold of to withdraw the plug from a jack so that
no inducement similar to the old form is offered to pull the plug out of the jack
by means of the cord alone.
Another important feature of our invention is the provision of an electric lamp
such as 4 or a disc such as Figure 8, bearing a number or character fixed in the
back end of the plug to form a visual signal or indicator as the case may be
to enable an operator to trace any particular connection at a glance and to replace
correctly any given cord from the complex set at the switchboard. Thus, lighted
lamps may indicate either " engaged" or disengaged" lines. The lamp is
preferably fixed in a socket such as 9, the said socket being fitted into a short
tubular holder which is slid over the end of the casing, up to the said shoulder
and may be secured in place by means of a screw as above stated. There are
other obvious ways of fitting this lamp in the end of the casing and we do not
confine ourselves to the precise way above specified.
The disc which may replace the lamp may be fitted in the end of the removable
capping piece or socket 3. This disc is preferably made of ivory.
When a lamp is provided in the end of the plug as shewn in Figure 1 the wires
of the lamp may be led one to the casing of the plug as shewn at 10 and the
other to the sleeve as shewn at 11 the two wires of the connection-cord being
led, one to the sleeve and the other to the tip-section 12.
In order to make provision for this lamp circuit, the plug is either made a
three-way one and connected to a two-way cord or double conductor as shewn in
Figure 1, or it is made a two-way plug and connected to a three-way cord or
treble conductor.
The three-way plug is formed by dividing the sleeve and insulating the parts
from each other and from the casing.
Both the lamp and the disc may be employed in one and the same plug, the
disc being fixed in front of the lamp, that is, in the rear end of the plug and
preferably made of glass, horn or other suitable transparent substance.
Furthermore, the number or character may be marked on the glass of the lamp
itself if desirable.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed, we declare that what
we claim is:-
1. In a connecting-plug for electrical switch-boards, the combination with the
casing of the plug, of a lateral aperture therein adapted to admit the end of the
connection-cord and hold it firmly at a fixed angle, substantially as described.
2. In a connecting-plug for electrical switch-boards, the combination with the
casing of the plug, of the lateral aperture adapted to admit the end of the con-
nection-cord and of a socket at the rear end of the plug adapted to receive an
electric lamp, said lamp and connection-cord and means for connecting the wires
with the lamp and plug, substantially as and for the purposes described.
3. A three-way connecting-plug for electrical switch-boards, consisting of the
combination with the casing, the tip-section and a two-way connection-cord, of
the lateral aperture in the casing and a sleeve-section insulated from the casing,
substantially as and for the purposes described.
4. In a two-way connection-plug for electrical switch-boards, the combination
with the casing, of the lateral aperture therein, the socket, the lamp therein, and
a three-way connection-cord the wires in which are electrically connected with
the plug and the lamp, substantially as described.
5. In a connection-plug for electrical switch-boards, the combination with the
rear end of the plug, of a disc bearing a number or other distinguishing sign,
as and for the purpose described.
6. In a connection-plug for electrical switch-boards, the combination with the
rear end of the plug, of an electric lamp and means for supplying and conveying
electric energy to light said lamp, as described.

page_text: 7. In a connecting-plug for electrical switch-boards, the combination with the
rear end of the plug, of an electric lamp and a transparent disc closing the
extremity of the plug behind the lamp, and means for supplying and conveying
electric energy to light said lamp, as described.
Dated this 1st day of November 1899.
PHILLIPS & LEIGH,
No. 22, Southampton Buildings, Chancery Lane, London, W.C.,
Agents for the Applicants.