Improvements in Electric Cables.
Year: 1896

page_text: Improvements in Electric Cables.
I, GEORGE HINDE NISBETT, of "Ashfield," Huyton, in the County of
Lancaster, Engineer, do hereby declare the nature of this invention to be as
follows:-
This invention has reference to electric cables in which a lead or like metal
sheathing is employed; and it has for its object to construct a cable of this class
or kind, in which the defects inherent in such cables, as usually constructed, are
obviated.
When a fault occurs in a cable of the class above specified, between the
conductor and the lead sheathing, the current causes an arc to be set up, resulting
in the production of great heat at the point of the fault, and the melting or
damage of the sheathing and cable. In some cables of this kind, attempts to
obviate the difficulties referred to have been made, and this has been done by
armouring the cables, that is, the lead sheathing has had covered or wound about
it, strips of steel or equivalent metal, and such steel or metal having a higher
melting point than lead, and being connected in parallel with it, has helped to
convey the current away to earth, and this has limited the damage due to the fault
to the cable itself, i.e. has prevented the fault having effects outside the cable.
Now according to the present invention, the obviation of the defects hitherto
existing in cables of this class, and the damage to which they are now subject, is
effected by constructing such cables with steel, copper, or other suitable metallic
covering outside and upon the insulation, and again applying outside this the lead
sheathing. The steel, copper, or other suitable metallic covering is conveniently
applied in strips or bands of any convenient section, and preferably they are
wound on the insulation in the form of as bands or tapes spirally, the thickness and
dimensions of the bands or strips depending upon the size of the conductor in the
cable, and the thickness of the lead, and other circumstances. This metal band or
strip covering, and the lead sheathing, are preferably in metallic continuity
throughout their length. By this construction, should a fault or leakage between
the sheathing of the cable and the conductor take place, as the steel or copper
covering strip or band has large conductivity, and a high melting point, and
being connected in parallel with the lead as a conductor, the path for the
current to earth is rendered as easy a one as possible, and it is safely conveyed to
the earth without such an amount of local heating as will melt the lead or
sheathing.
CHEESBROUGH & ROYSTON,
15 Water Street, Liverpool, Applicant's Patent Agents.

page_text: I, GEORGE HINDE NISBETT, of "Ashfield," Huyton, in the County of
Lancaster, 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 has reference to electric cables in which a lead or like metal
sheathing is employed; and it has for its object to construct a cable of this class
or kind, in which the defects inherent in such cables, as usually constructed, are
obviated.
When a fault occurs in a cable of the class above specified, between the
conductor and the lead sheathing, the current causes an are to be set up, resulting
in the production of great heat at the point of the fault, and the melting or damage
of the sheathing and cable. In some cables of this kind, attempts to obviate the
difficulties referred to have been made, and this has been done by armouring the
cables, that is, the lead sheathing has had covered or wound about it, strips of
steel or equivalent metal, and such steel or metal having a higher melting point
than lead, and being connected in parallel with it, has helped to convey the current
away to earth, and this has limited the damage due to the fault to the cable itself,
i.e. has prevented the fault having effects outside the cable. Now according to the
present invention, the obviation of the defects hitherto existing in cables of this
class, and the damage to which they are now subject, is effected by constructing
such cables with steel, copper, or other suitable metallic covering outside and upon
the insulation, and again applying outside this the lead sheathing. The steel,.
copper, or other suitable metallic covering is conveniently applied in strips or bands
of any convenient section, and preferably they are wound on the insulation in the
form of or as bands or tapes spirally, the thickness and dimensions of the bands or
strips depending upon the size of the conductor in the cable, and the thickness of
the lead, and other circumstances. This metal band or strip covering, and the lead
sheathing, are preferably in metallic continuity throughout their length. By this
construction, should a fault or leakage between the sheathing of the cable and the
conductor take place, as the steel or copper covering strip or band has large
conductivity, and a high melting point, and being connected in parallel with the
lead as a conductor, the path for the current to earth is rendered as easy a one as
possible, and it is safely conveyed to the earth without such an amount of local
heating as will melt the lead or sheathing.
The drawing accompanying this specification shews a cross section of a cable
according to my invention."
a represents the conductor, 6 the insulation, c the lead sheathing or covering,
and d the band or strip of metal having a a relatively high melting power, such as
copper, steel, or other suitable metal, placed over the insulation and directly under
the lead sheathing.
It is to be stated that I am aware that a lead covered electric cable has been
constructed with a metallic conductor within the lead covering, to serve as a return
conductor within such cable; whereas in my cable this interposed metallic covering
or sheathing normally carries no current, and only comes into operation on the
occurrence of a fault, and then and thereafter acts in such a way as to help the
lead sheathing both to resist the action of the heat generated at the fault, and to
safely carry the leakage current along until a suitable "ground" on the cable
is made.

page_text: Having now particularly described and ascertained the nature of this inven
tion and in what manner the same is to be performed, I declare that what I
claim is
1. The herein described improvement connected with electric cables having a
lead covering for preventing the local melting of the lead covering on the
occurrence of a fault, and consequent formation of an arc, consisting of the
construction of such cables with a band or strip or strips of metal having a
relatively high melting power placed over the insulation, and under the lead
covering, in such a manner, as to afford a low resistance path to earth for the
electrical current on such occurrence of a fault, and formation of arc, such band or
strip or strips of interposed metal, being adapted normally to carry no current :
substantially as set forth.
2. In a lead covered cable, bands or strips of metal having relatively high
conductivity placed over the insulation and under the lead covering and arranged
in such a manner as to increase the conductivity of the sheathing of the cable
sufficiently to safely convey to earth any leakage of current there may be ;
substantially as set forth.
Dated this 12th dox of Narember 1896
CHEESBROUGH & ROYSTON,
15 Water Street, Liverpool, Applicant's Patent Agents.