Improvements in Electric Terminals and Switches.
Year: 1889

page_text: Date of Application, 28th Oct., 1889-Accepted, 7th Dec., 1889
COMPLETE SPECIFICATION.
Improvements in Electric Terminals and Switches.
I, HENRY INKSON HARRIS, of 61 Ossory Road, Old Kent Road, S.E. in the County
of Surrey, Electrician 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 :—
My invention relates to an improved form of electric terminal, which by a slight
modification, can be constructed to operate as a switch, the main feature of the inven-
tion being the enclosure of the contact making parts, in an insulated chamber, shut
off from communication with the external atmosphere, so that any sparking, which
may take place on making or breaking contact, is confined to the said chamber, and
in consequence, terminals or switches constructed according to my invention, may
be safely operated in mines containing explosive gases, in gunpowder magasines, or
other situations where the use of an ordinary terminal or switch might result in an
explosion.
In the accompanying sheet of drawings, Fig. 1 is a perspective elevation of a
terininal constructed in accordance with my invention; Fig. 2 is a sectional elevation
of the same through the centre, and Fig. 3 is a sectional elevation shewing the parts
disconnected; Fig. 4 is a perspective elevation, shewing the apparatus constructed as
a switch, and Fig. 5 is a sectional elevation of the same, through the centre.
Similar letters of reference denote similar parts throughout the drawings.
In Figs. 1, 2, and 3, representing the terminal, A is a metal cup secured by a
screw B, or other suitable device, to the base C, or instrument to which it is to be
applied. The cup A is cemented into a cylindrical tube D of vulcanite or other suit-
able insulating material. A cap E also formed of vulcanite, or other suitable insulating
material, is fitted to slide tightly over the tube D. It has fixed within it a conical
metal plug F, by means of a screw H or other device, and the interior of the cup A
is coned to the same taper as the said plug. One wire J of the circuit is fixed to H
and the other to B.
The cap E is surrounded by a metal case K. A rubber washer L is placed around
the wire J and a cap M, fitted to screw on the case K, compresses the said washer,
causing it to completely cover and insulate the joint between the wire J and the
screw H. The plug F and the cup A form the two contact surfaces of the terminal.
When the cap E is slid upwards, contact is broken, and when it is pushed down contact
is made. To lock the terminal in the latter position, any suitable device may be
employed. In the drawings, the case K is provided with a flange N, having a
notch P, which when the cap E is pushed down clears the head of a screw or
stud Q, fixed in the base C, and on rotating the cap, the flange N is held by the
head of the said screw, or stud. The twisting motion necessary to effect this,
causes, the plug F to rub in the cup A, and thus keep the contact surfaces clean and
in good condition. When contact is broken, any sparking which may take place
between the surfaces of F and A is enclosed in the insulated chamber formed by the
cap E and tube D, and if the cap be lifted completely off, as shewn in Fig. 3, the
contact will have been broken, and the sparking ceased, at the first part of the
upward movement of the cap and long before the chamber can become open to
the atmosphere.
The use of the rubber washer L is to prevent the possibility of sparking at the
joint formed between the wire J and screw H through a naked wire coming in contact
with the joint, or through an imperfection or breaking in the joint.
The switch, shewn in Figs. 4 and 5, is constructed substantially in the same
manner as the terminal, the difference consisting in the mode of operating the
cap E.
A tube R is affixed to the base C and has a slot S formed in it. This

page_text: slot is inclined for the greater part of its length, but terminates in a short hori-
zontal piece at the upper end. A screw or stud T is fixed into K and projects
through the said slot, and a handle U is fixed to the top of the cap E.
In the position shewn in the drawings, the pieces F and A are in contact, and the
circuit closed. To break contact, the cap E is rotated by the handle U, and the
stud T sliding up the inclined part of the slot S, causes the plug F to be withdrawn
from the cup A, and a slight further rotation causes the stud T to travel along the
upper horizontal part of the slot and hold the switch securely in this position.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what 1
claim is
1. An electric terminal or switch, having contact surfaces consisting of a cup A and
a plug F, enclosed within insulating tubes D and E, substantially as and for the
purposes herein set forth.
2. An electric terminal or switch, having contact surfaces consisting of a cup A
and a plug F, enclosed within insulating tubes D and E, and provided with an
insulating washer L, secured by a cap M, all substantially as and for the purposes
herein set forth.
3. An electric terminal constructed substantially as herein described and shewn
with reference to Figs. 1, 2, and 3 of the accompanying drawings.
4. An electric switch constructed substantially as herein described and shown with
reference to Figs. 4 and 5 of the accompanying drawings.
Dated this 28th day of October 1880
AMBROSE MYALL,
21, Cockspur Street, London, S.W., Agent for the Applicant.