Improvements in Earthing Devices and Safety Fuses for Electrical Circuits.
Year: 1899

page_text: Date of Application, 20th Dec., 1899
Complete Specification Left, 20th Sept., 1900-Accepted, 8th Dec., 1900
PROVISIONAL SPECIFICATION.
Improvements in Earthing Devices and Safety Fuses for Electrical
Circuits.
I, LOUIS JOHN STEELE, of Plume Works, Aston, Birmingham, in the County
of Warwick, Electrical Engineer, do hereby declare the nature of this invention
to be as follows:-
This invention is an improved earthing device, or safety fuse, for use in
electrical circuits for ensuring an automatic connection to earth, or to safety,
if an abnormal and dangerous current should at any time arise therein.
An earthing device according to this invention is constructed as follows:-
Located within a box-like casing connected in a suitable way to earth is a con-
ductive portion comprising two plates connected with the circuit to be pro-
tected and insulated from the casing, the said portion constituting the earth
terminal of the protected circuit. Standing up from one of the plates, as afore-
said, is a peg upon which is threaded a carrier for a fuse wire. The said carrier
is formed of two metal discs connected face to face with a layer of perforated
micanite between them, and the fuse wire, which is in the form of a loop, passes
round the boundary edge or periphery of one of these discs which is insulated
from the conductive portion, as aforesaid, and the post, by the micanite layer and
a non-conducting bush, the latter let into the centre of the disc to surround the
post and face the micanite layer. A screwed thumb nut engages the post above
the discs, and holds the fuse carrier in position thereon. The outer end of the
looped fuse wire passes round a circular piece carried upon the one end of a
short arm fulcrumed to a second arm jointedly connected to the casing of the
device. An under-lever is also fulcrumed to the second arm to move as one
piece with the short arm. The fulcrum to this under-lever is formed by a stud
standing up from the bottom of the casing and a slot in the under lever with
which the said stud engages, the said fulcrum becoming thereby a shifting one.
A yielding contact piece is carried upon the second arm, for engaging the plates,
before described, of the conductive portion, by forcing itself wedge-like between
them by the action of a spring, the action of said spring however being held in
check by the looped fuse wire so long as the said fuse wire is intact or "not
blown." When the said contact piece engages the plates of the conductive
portion the protected circuit is put to earth.
In action, the under-lever is operated, by pulling inward the free end of the
short arm, to withdraw the contact piece from engagement with the plates by
moving the second arm-this through the shifting fulcrum, and when the fuse
wire passes round the circular piece on the said free end the said contact piece is
held, against the action of the spring, out of contact with the plates of the
conductive portion, until such time as the fuse wire "blows," when the said
spring acts upon the second arm to make connection between the contact piece
and the plates.
The blowing of the fuse wire takes place immediately a current passes through

page_text: the conductive portion sufficiently strong to jump the air gaps formed by the
perforations in the micanite layer of the fuse, the thickness of the said layer
being accurately predetermined to adjust the sparking distance between the
discs of the fuse.
The whole of the levers and arms are neatly enclosed in the box-like casing
adjacent to the conductive portion, and the said casing is closed by a lid. .
Tied the 10th
STY
1000
W. P. THOMPSON & Co.,
11, Burlington Chambers, New Street, Birmingham,
Patent Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in Earthing Devices and Safety Fuses for Electrical
Circuits.
I, LOUIS JOHN STEELE, of Plume Works, Aston, Birmingham, in the County
of Warwick, 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:-
This invention is an improved earthing device for use in an electrical circuit
for ensuring an automatic connection of the said circuit to earth if an abnormal
and dangerous current should at any time arise therein.
The said device is set forth in the annexed sheet of drawings in plan in Fig. 1
and in vertical section in Fig. 2, the position of the parts being one
66 set" or
shutting out the earth connection from the circuit. In this device a fuse wire
is used, and the particular manner in which it is applied and fitted to form a
part of the earthing device is particularly shown by the section Fig. 3. Fig. 4
is a section of a part forming an earth terminal to the device in the protected
circuit.
In this sheet of drawings 2 represents a casing of a box construction to enclose
and form a carrier for the active parts of the device, the said casing being con-
nected in a suitable way from a connection 3 to earth. 4 represents a conductive
portion (a portion capable of conducting electrically) comprising two plates 5
and 6, the first named plate connected to the circuit to be protected and insulated
from the casing 2, and the last named plate connected to the casing 2 the said
portion constituting the earth terminal of the protected circuit. 5*, Fig. 1, is
a connection screw for the wire of the protected circuit, and is in electrical
communication with the plate 5. A screwed post or peg 7 stands up from the
plate 5, and upon it is placed a carrier 8 for the fuse wire 9, the said carrier
being formed by two circular plates 10, 12, connected together with a layer 13
of perforated micanite between them. The fuse wire 9, which is in the form of
a loop, passes round the boundary edge or periphery 14 of the plate 12, the latter
being insulated from the plate 10, which is in electrical communication with the
post 7 and the plate 5, by the micanite layer, as aforesaid, and a non-conducting
bush 15, let into the centre of the plate 12 to surround the post 7 and face the
micanite layer. A screwed thumb nut 16 engages the post 7 and holds the fuse
carrier 8 in position thereon and prevents the parts of it becoming in any way
displaced.
The outer end of the looped fuse wire 9 passes round a circular disc 17 carried
upon the one end of a short arm 18 fulcrummed at 19 to a second arm 20 jointedly
connected at 21 to the casing 2; an under-lever 23 being also fulcrummed to the

page_text: arm 20 at 19 so as to move as one piece with the arm 18. The fulcrum to this
under-lever 23 is formed by a stud 24, standing up from the bottom of the
casing 2, and a slot 25 in the under-lever with which the said stud engages, the
fulcrum becoming thereby a shifting one. A yielding contact piece 26 is carried
upon the arm 20 for engaging the plates 5 and 6 by forcing itself wedge-like
between them by the action of a spring 27, which, however, is held in check
by the looped fuse wire so long as the said fuse wire is intact or "not blown."
When the contact piece 26 engages the plates 5 and 6, the protected circuit, of
which the plate 5 forms a part, is put to earth.
In action, the under-lever 23 is operated, by pulling inwards the free end of
the armi 18, to withdraw the contact piece 26 from engagement with the plates 5
and 6, by moving the arm 20, and when the fuse wire passes round the disc 17
on the said free end holds it in position represented in Fig. 2, viz:-against the
action of the spring 27, until such time as the fuse wire 9 "blows," when the
spring 27 acts upon the arm 20 immediately the arm 18 is released from being
held in by the fuse wire.
.
The "blowing" of the fuse wire takes place immediately a current passes
through the plates 5 and 10 sufficiently strong to jump the air gaps of the per-
forations in the micanite layer 13, the thickness of the said layer being accurately
predetermined to adjust the sparking distance between the plates 10 and 12.
The arm 18 is mounted on the contact arm 20 at 19 and the under-lever 23 is
also carried by arm 20. The spring 27 constantly tends to swing the arm 20
on its pivot or joint 21 towards the conductive portion 4, so that the contact
arm 20 shall engage the plates 5 and 6. The arm 20 is however, controlled in
the direction against the spring 27 by the under-lever 23 and the arm 18 through
the fulcrum stud 24 and the slot 25. The retention of the arm 18 by the fuse
wire is in a similar direction to the action of the spring 27, whereas the fuse
wire in action holds the arm .20 against the spring 27. This comes about by
the arm 18 being fulcrumed by the under-lever 23 and the stud 24 to the casing
and used as another lever to move the arm 20 against the spring 27, the fulcrum
of the under-lever 23 being a shifting one, or one capable of compensating for
the radial movement of the arm 20 in bringing forward the contact piece 26 to
engage the plates 5 and 6. Assuming that the fuse wire has "blown" and that
the contact piece 26 engages the portions or plates 5 and 6, to
break the contact between the parts 26 and 5 and 6, the arm 20 is moved
against the action of the spring, so as to withdraw the contact piece, by pulling
inwards (towards the carrier 8) the free end of the arm 18 and with it the under
lever 23 (it being a rigid part), and rocking them both upon the stud 24; there-
fore the lever 20 is moved against the spring by another lever 18 and 23, ful-
crumed by the parts 24 and 25.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is: -
First. In an earthing device, the combination of a conducting portion forming
an earth terminal of the protected circuit, a looped fuse wire connected thereto
so as to be insulated by a perforated micanite layer, an under-lever having a
shifting fulcrum and to which the other end of the looped fuse wire is indirectly
connected, a jointed arm carrying a contact piece and to which the under-lever
is jointedly connected, and a spring acting upon the arm carrying the contact
piece substantially as described.
Second. In an earthing device, the combination of a conducting portion form-
ing an earth terminal of the protected circuit, a looped fuse wire connected
thereto by plates 10, 12, having between them a perforated micanite layer, a
jointed arm carrying a contact piece and fitted with a spring, an under-lever
jointedly connected to said arm and having a slot within it engaging a fixed
stud to form a shifting fulcrum, and an arm connected to the under-lever so as

page_text: to move as one with it and over whose free end the other end of the looped fuse
wire passes, substantially as described.
Third. In an earthing device, the combination of a suitable box-like casing, a
conducting portion 4 arranged therein, a looped fuse wire 9 connected to the
said portion by plates 10 and 12, micanite layer 13, bush 15 and post 7, a jointed
arm 20 carrying a contact piece and fitted with a spring, an under-lever 23
jointedly connected to arm 20 and having within it a slot 25 engaging
stud 24 on the casing, an arm 18 connected to the arm 20 so as to move as one
with the under-lever, and a disc 17 around which the other end of the looped
fuse wire is adapted to take, substantially as described.
fixed
Fourth. In an earthing device, the combination of a conducting portion 4
forming the earth terminal of the protected circuit, a looped fuse wire 9 con-
nected thereto by a carrier 3, a lever to which the other end of the looped fuse
wire is indirectly connected, and which holds from contact with the portion 4 a
contact piece, and a spring exerting an influence upon the said lever, substantially
as described.
Dated 1: 10+1 of Cantamh 1000
W. P. THOMPSON & Co.,
11, Burlington Chambers, New Street, Birmingham,
Also at Liverpool, London and Manchester,
Patent Agents for the Applicant.