Improvements in Electric Safety-fuses.
Year: 1898

page_text: Date of Application, 21st Sept., 1898-Accepted, 26th Nov., 1898
Improvements in Electric Safety-fuses.
A communication from abroad by the ACTIEN-GESELLSCHAFT ELEKTRICITAETSWERKE
(vorm. O. L. KUMMER & Co.), of Niedersedlitz, near Dresden, Germany.
I, WILLIAM LLOYD WISE, of No. 46, Lincoln's Inn Fields, in the County of
London, Chartered Patent Agent and Consulting 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:-
In a safety-fuse according to this invention, it is intended, by means of a simple
adjustment of the fuse, to prevent the unintentional insertion of too strong
fuse-cartridges.
In such a fuse (an example of which is shown in vertical section in Fig. 1, and in
plan in Fig. 2, of the accompanying drawings), when the cartridge is screwed on,
the current passes through the first connecting piece A¹, the lead wire P, which is
situated in the porcelain cartridge P, the attaching-screw S on the fuse-cartridge,
and lastly through the second connecting piece A³. When the current is too strong,
the circuit, which has a greater cross sectional area than corresponds to the lead wire,
is broken by the fusing of the lead wire Px in the porcelain cartridge P and is thus
rendered safe. If, on the contrary, a cartridge is screwed on having a lead wire of
greater cross sectional area than corresponds to the circuit, the latter is endangered
because with a higher current-strength the connected circuit is destroyed and the
lead wire remains uninjured.
The latter case may be caused by carelessness or mistake and not only can the
circuit be damaged thereby, but fires may also be caused. This danger is now
intended to be prevented by the safety-device herein described.
The fuse proper consists of two main parts :-
(1.) The plate F of porcelain with brass connecting and circuit-making
pieces A¹ and A2 and the adjustable attachment-screw S for the fuse-cartridge ;
and
(2.) The fuse-cartridge P consisting of the porcelain body with the inserted lead
wire P*.
The fuse itself is constructed for a current strength up to 15 ampères. To this
there belong four fuse-cartridges, of which
No. 1, for 4 ampères, protects a copper wire of 1.0 sq. mm.,
No. 2, for 6 ampères, protects a copper wire of 1.5 sq. mm.,
No. 3, for 10 ampères, protects a copper wire of 2.5 sq. mm.,
No. 4, for 15 ampères, protects a copper wire of 4.0 sq. min.
If, now, one of these fuse-cartridges, which must be selected according to the
circuit, is to be screwed on, first the attachment screw S must be adjusted to the
cartridge P if the latter is to fit. The adjustment can, however, only be made
by an expert, and by means of a special key R, shown in plan and in cross
section in Figs. 3 and 4 respectively. All four fuse-cartridges for the different
[Price 8d1

page_text: current-strengths are completely identical, as regards their main parts, which is very
important as regards their manufacture, and they differ only in the various
thicknesses of their lead wires P*, which can be easily inserted, and in their
attaching female screw-threads G, each of which is shorter by 3 mm. than the
corresponding thread of the cartridge for the next lower current-strength; the
effective length of the female thread of a cartridge can be easily adjusted by
means of a screw S¹ that is placed in its upper end.
It will be easily perceived that as the female screw-thread of a cartridge P is
shorter in each case, the screw-thread of the attaching screw S must also be shorter
if the cartridge is to make contact with the circuit-making surface C, which is
situated in a definite position. Otherwise, the cartridge will not make contact with
this surface and the circuit will be broken, and this will take place if a too strong
cartridge be screwed by mistake upon a weaker fuse.
Now, for the purpose of altering the effective length of the attaching-screw S by
3 mm. in each case, there is provided in the lower connecting piece A² a rotary but
not longitudinally movable nut M in which the attaching-screw fits.
This screw is
provided at its lower end with a square portion V and moves in a guide, so that it
cannot rotate, but can be moved up or down to the extent of four times 3 mm. only
by rotating the nut M by means of the special key R. The adjusting key R is
placed over the attaching-screw S until the collar B provided on the key abuts
against the circuit-closing surface C. It can now be seen through a lateral aperture,
and by means of a scale R¹ on the key, for what cartridge or current-strength the
thread of the attaching-screw has been set.
If the length of the thread of the attachment screw S does not agree, the nut is
rotated by means of the key R and the decrease or increase in the length of the screw-
thread is noted by means of the said key until the upper edge of the screw
indicates the desired current strength on the scale. Thus, for example, on the
key, h¹ indicates the height of the projecting screw for a cartridge for a working
current strength of 15 ampères. The corresponding cartridge will now be able to be
screwed thereon, and will reach the circuit closing surface C, whilst a cartridge for a
higher current strength if screwed upon this adjusted length of screw-thread, will
not be able to touch the surface C, but will remain at least 3 mm. away from the
latter, so that the requirement above stated is fulfilled.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
An electric safety-fuse adapted for the use of fuse-cartridges, in which, for the
purpose of preventing fuse-cartridges having too thick fuse-wires from being inserted
so as to conduct the current, the screw-spindle S on which the cartridges are to be
screwed is adapted to be adjusted as to its height by means of a nut M, which is
secured against longitudinal movement and can be rotated only by means of a
suitable key R provided with a scale, in such a manner that the projecting length of
the screw-thread of the spindle S can be suited to the corresponding lengths of the
screw-thread G in the cartridges.
Dated this 21st day of September 1898.
W. LLOYD WISE,
46, Lincoln's Inn Fields, London, W.C., Chartered Patent Agent.