Improvements in Apparatus for Testing Insulation Resistance of Electric Wires.
Year: 1890

page_text: Date of Application, 1st Nov., 1890
Complete Specification Left, 30th July, 1891-Accepted, 10th Oct., 1891
PROVISIONAL SPECIFICATION.
Improvements in Apparatus for Testing Insulation Resistance of
Electric Wires.
1, JOHN JAMES RATHBONE, of 10 Bramley Road, Notting Hill, Middlesex,
Electrical Engineer, do hereby declare the nature of this invention to be as
follows:-
The object of my invention is the employment of an electric generator of high
electromotive force, in conjunction with an electrometre for testing insulated, electric
wire for small leakages, and for indicating approximately the amount of such
leakage.
It is well known that electric currents of high tension will attract light bodies
within certain limits, I take advantage of this fact.in my electrometre as follows:
I employ a magnetic compass with preferably, a piece of wood fixed across it, this
wood is. attached to the needle and revolves with it.
"The compass is fixed' to a moveable or pivotted glass base or other suitable
insulating material. On this base, I fix a terminal near to the needle but not in
contact with any part of it, the position being so arranged that the needle is pulled
over, when the current generator is applied, for a distance of about three eighths of
an inch, providing the circuit to be tested. is free from leakage. For this purpose,
the line wire to be tested has one. end removed and affixed to the terminal, so that
on applying the generator to the terminal the needle is (deflected) pulled over to a
stop arranged in its path. If it is not free from leakage, the needle will not be
deflected so much by reason of the current going to earth. The amount of deflection
can be indicated by turning the base on its pivot for a pointer on the base to move
over a graduated scale the distance required to bring the needle opposite the
terminal by the current, the degrees of deflection representing the amount of
leakage.
The graduated scale is on a plate of glass or other insulator. For testing
purposes, I use a generator, such as a Clark's Electric Gas Lighting Instrument,
with the exception that the long tube is shortened to about an inch in length to
keep it out of reach of its centre wire and thus prevent sparking across.
The whole of the apparatus can be made to weigh less than one pound in working
order.
COMPLETE SPECIFICATION.
Improvements in Apparatus for Testing Insulation Resistance of
Electric Wires.
I, JOHN JAMES RATHBONE, of 10 Bramley Road, Notting Hill, Middlesex,
Electrical Engineer, 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 :-
According to my invention I employ an electric generator of high electro-
motive force, such as a frictional electric machine, in conjunction with an electro-
metre for testing insulated electric conductors for small leakages, and for

page_text: indicating approximately the amount of such leakage, as I shall describe referring
to the accompanying drawings.
Fig. 1 is a section and Fig. 2 is a plan of my apparatus which consists of a
magnetic compass needle A with a light index B fixed across it, and attached
to the needle so as to move with it.
The needle is mounted on a base C of insulating, material, on which basc I
fix a terminal D near to the end of the index B which may be in the form of a
disc as shewn, the position being so arranged that by the attraction which the
terminal D exerts on the index the needle is pulled over a certain distance, when
the current generator is applied, by connecting it to a post E which is in
connection with the line wire and with the terminal D.
If there be leakage from the line wire, there will be less attraction of the
index by reason of some of the charge going to earth.
In this case, the base is turned partly round so as to bring the terminal D
near enough to the index to attract it up to it, and the extent of the leakage
may be estimated by the number of degrees the base is moved round as indicated
on a scale F.
For ordinary testing purposes a convenient form of generator is that employed
in some cases for electric gas lighters.
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 I
claim is :-
Apparatus for testing insulation of electric wires consisting of a magnetic
needle which is deflected more or less from its polar position by the attraction
exerted by a static charge in the wire on an index attached to the magnet
substantially as described."
Dated this 30th day of July 1891.
ABEL & IMRAY,
Agents for the Applicant.