Improved Means for Conveying Currents of High Tension, and in Appliances used for this Purpose.
Year: 1892

page_text: Date of Application, 17th Feb., 1892
Complete Specification Left, 17th Nov., 1892-Accepted, 17th Feb., 1893
PROVISIONAL SPECIFICATION.
Improved Means for Conveying Currents of High Tension, and in
Appliances used for this Purpose.
I, SEBASTIAN ZIANI DE FERRANTI, of 120 Fellows Road, Hampstead, in the
County of Middlesex, Electrician, do hereby declare the nature of this invention
to be as follows:-
In order to transmit electricity of high tension to a considerable distance it has
hitherto been the custom to use either an insulated cable laid in the ground, or a
bare copper wire fixed on porcelain insulators-in the way in which telegraph wires
are commonly supported. Where the current has been of very high tension the
insulators have been of a modified form, and have had an oil dish round about them
to improve their insulating power. Another method is to have a copper insulated
cable hung from a suspender wire, and in the Specification of Patent No. 12418, in
the year 1887, I described improved means of doing this, which have been
extensively applied.
Cables buried in the ground, and also insulated cables hung overhead are for
many reasons disadvantageous, principally on account of their expense, and secondly
on account of their capacity.
The bare wire system is generally speaking, the most desirable but it has been
found very difficult to maintain the insulation of the lines and also great trouble has
been given by the high tension current piercing the insulators.
One method by which I carry overhead wires to avoid these objections is by
means of a special insulator, which consists of a porcelain or glass rod held in a
clamp at the bottom to fix upon the poles, and having a cap fixed on its top end,
which holds the wire to be insulated, or it may be that the wire may be passed
through a hole or slot in the end of the insulating rod instead of being held by a
cap fixed on the rod. The rod may under certain circumstances be hung from the
fixing on the pole, and the wire passed through or hung by means of a cap from its
lower end.
If these insulating rods are made of sufficient length they form a very certain
means of insulating an overhead conductor, as there is no metal inside the rod as
in the case of insulators cemented on to an iron bolt, and the rod cannot therefore
be pierced by a current.
The only way in which its insulation can suffer is by surface leakage. In most
cases it is found desirable to cement or fasten, by means of an insulating material,
glass or porcelain washers or washers of other insulating material on to the rod
with a small interval between each, the surface is then enormously increased
between the ends of the rod. In fact the current would then have to leak over a
great many feet of surface before it could get to earth or to the other conductor.
These rods may be so formed that they may be hung from the poles or stood in
sockets so as to be easily removed, when they may be cleaned by immersing in hot
oil or other dissolving fluid, and also if found desirable dipped in some form of
parafine, wax, oil, or other insulating substance, which will leave them with a
surface which will prevent moisture depositing upon them for a considerable period,
and thus improve the insulating quality of the surface.
Two or three rods may be grouped together so as to give greater strength to the
insulating support for the wires. The discs which are threaded on to the rods may
have their outer edges turned up a little so as to admit of each one forming a
shallow oil cup.
These rods may be moulded with the discs or projections upon them, but a better

page_text: quality of article is obtained by making the insulators composite. One method of
putting on the discs is to thread them on to the rods with rubber or other flexible
washers in between them, and then tighten up from each end so as to make the
flexible washers make a good contact between the rod and the various washers.
An adhesive and insulating substance may also be used in this process.
Another means of efficiently suspending the high pressure conductors is to carry
them from the pole on a long length of cord of silk, manilla or other flexible
insulating material. The cord may also be prolonged for a corresponding length
below the wire and held tight in order to prevent the wires swinging about. These
cords are made of sufficient length to give the necessary insulation. I prefer to
soak these cords in an insulating oil or wax in order to make them as far as
possible waterproof, and to confine moisture to their surface and to prevent it
entering into the body of the cord.
In order to maintain them in an oily condition they may terminate in oil cups at
each end, and there may also be an oil cup on the cable fastening where the upper
and lower cords are attached. The cords will thus act as wicks, and keep them-
selves fully saturated with oil, which will of course help to maintain their insulating
qualities.
In some cases where insulating rods are used I cover their surface with a thin
coating of fibrous material and saturate this by preference with insulating oil or
wax.
Where alternating currents are used I find that if a little moisture is deposited
upon the surface of an insulator and the distance between the points of high
E.M.F. is sufficiently great, that enough current will he conducted by the moisture
to dry it up, and so render the insulator perfect. Where the surface is solid
porcelain or other insulator with a smooth surface the result of moisture is generally
the formation of an arc, or there is a sufficient amount of moisture deposited to
form a permanently bad insulation. Now I avail myself of these facts in the above
system. The suspending cords and also the fibrous material on the surface of the
insulators in the first place do not get much moisture deposited on their surfaces.
In the second place what is deposited is evenly distributed, and thus in times of
damp or wet weather a small amount of current flows and maintains the insulation
of the insulators in very perfect condition.
With both these systems, as also with the plan of insulators as ordinarily used, I
prefer to enclose the insulators, and in fact to cover in the space around the pole
which carries the insulators with a small house or box, with holes of considerable
size in relation to the diameter of the line wire for it to pass through. These holes
may be sheltered against rain and moisture blowing in by means of baffle plates at
a short distance inside and outside the box. The holes in the box may also be
fitted with insulating tubes, and also have baffle plates as before.
By this means a box is obtained which although the insulator is thoroughly in
contact with the air prevents the deposition of a great deal of dirt and moisture
upon the insulators or cords which carry the wires, and thus maintains their
insulation in very much better condition than it would otherwise be.
In some cases the holes in the box are nearly covered by a diaphragm of thin
fibrous material, but this, as also nearly covering the holes with any other form of
insulator, has a certain disadvantage that under certain circumstances sparks will
continuously jump from the wires on to these insulators, which can only be considered
as partial insulators. In practice the size to make these holes for the wires
entering, and the extent of covering up of these holes with screens will be found for
each particular case and climate.
In cases where the roads or country along which the conductors pass is much
frequented, or where danger from the wires is anticipated I insulate one of the
conductors as above explained on either specially good insulators or suspended in a
fixed position by means of insulating cords round which as I have explained I
prefer to put a protecting box or covering. This lead or conductor represents the
central conductor in concentric cable and the outside conductors of the concentric

page_text: cables I replace by wire stretched from pole to pole upon insulators placed round
about the central conductor and central insulator. These outside or return
conductors can be placed outside the projecting box. It is desirable to make the
return conductor in as many wires as possible, so as to make as complete a network
round about the insulated or outgoing conductor as possible. These external
conductors I connect to earth either at several places or at one place along the
line, preferably at the dynamo end, and so the potential upon them can never be
greater than that due to the copper loss upon the line. These external conductors
may be threaded through rings every few yards in order to keep them in as nearly
as possible a circular form and they may also be held in rings at the posts which
rings are carried on insulators.
The conductors may also be so arranged that they form an open spiral round
about the outgoing conductor, by this means it is impossible to get at the inner
conductor without breaking or going between the outside or earth conductors.
Also if the central conductor falls it will be immediately short-circuited, on the
outer ones, and thus prevent its doing any damage.
When transmitting currents of high tension through long electric mains it
prequently happens that certain parts of the circuit and apparatus are charged to
a pressure considerably in excess of the maximum working pressure.
In order to overcome this difficulty I place non-inductive resistances of suitable
form and dimensions across the poles of the dynamo, across the poles of the trans-
formers and across the mains at various places. I may also connect the same to
earth by such means.
The inductive resistance may be made of very fine wire or material of high
resistance. They may be made of strings or wicks kept moist with water so as to
be of very high resistance, and to dissipate a very small quantity of current only, or
they may be made of a number of cells of water in series with electrodes dipping
into each cell.
Or they may consist of long tubes filled with water, and being of sufficient
section to conduct any desired amount of current. The object to be sought after
being that they should have as little self-induction as possible.
Their
Moreover the liquid resistances are desirable from the point of view that a
momentary rush of current can take place through them more easily.
resistance only coming up after a current has flowed for some little time.
These resistances will form as nearly as possible a non-inductive path through
which any extra or charge currents may be with facility discharged, and so
prevent the critical state which gives rise to charge currents appearing upon and
damaging apparatus used in the system.
These dischargers may also be used as lightning arresters for continuously con-
ducting away and transmitting to earth any electrical charge, rather than letting it
accumulate until it has reached a sufficient E.M.F. to break down the insulation
of the system.
In some cases it is desirable to use a number of these dischargers, as well as
forming one circuit in series with an air gap between points or electrodes set at a
distance which is just too great for the ordinary E.M.F. to spark across.
When
the charge current gets to sufficient pressure to escape it will do so across the air
space provided rather than break down the insulation of the system, but no great
quantity of current will flow. The arc will go out on account of the high
resistance of the cells in series with it there not being sufficient quantity of current
for the arc to maintain.
These discharge points may have a blast of air between them, or may have a fan
working to help the blowing out of the arc.
In some cases I prefer to make the discharge points in such a way that one of
them consists of a conducting point nearly touching or at a moderate distance
above a dish of water which is in connection with the other pole. In some cases a
second point may project up through the water or liquid to near the surface, or
several points may be used above the surface of the water, in this way any very

page_text: small quantity of current from high tension will easily jump to the water and so be
discharged, but no current of any quantity will be able to follow this up.
This apparatus may be used as a high pressure discharger or as a lightning
protector.
In some cases I make dischargers or lightning protectors of 2 points or 2 tubes
closely facing each other, and across which the dynamo current will not jump.
When a lightning or other discharge takes place, rather than hurt the apparatus it
will jump across this air space, and be immediately blown out by the strong
blast emerging from the two tubes or across the points, produced by a fan or
blower.
Dated this 17th day of February 1002
CARPMAEL & Co.,
Agents.
COMPLETE SPECIFICATION.
Improved Means for Conveying Currents of High Tension, and in
Appliances used for this Purpose.
I, SEBASTIAN ZIANI DE FERRANTI, of 120 Fellows Road, Hampstead, in the
County of Middlesex, 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 :-
In order to transmit electricity of high tension to a considerable distance it has
hitherto been the custom to use either an insulated cable laid in the ground, or a
bare copper wire fixed on porcelain insulators in the way in which telegraph wires
are commonly supported. Where the current has been of very high tension the
insulators have been of a modified form, and have had an oil dish round about them
to improve their insulating power.
Another method is to have a copper insulated cable hung from a suspender wire
and in the Specification of Patent No. 12418 in the year 1887 I described improved
means of doing this, which have been extensively applied.
Cables buried in the ground, and also insulated cables hung overhead are for
many reasons disadvantageous, principally on account of their expense, and secondly
on account of their capacity.
The bare wire system is generally speaking the most desirable but it has been
found, very difficult to maintain the insulation of the lines and also great trouble
has been given by the high tension current piercing the insulators.
One method by which I carry overhead wires to avoid these objections is by
means of a special insulator such as is shewn by Figures 1 and 2 which consists of
a porcelain or glass rod held in a clamp at the bottom to fix upon the poles, and
having a cap fixed on its top end, which holds the wire to be insulated.
In Figures 1 and 2 a is an arm projecting from the post is a metal socket
with a tongue passing through the arm and secured by a nut, c is a porcelain or
glass rod screwed into the socket with cement. d is a cap screwed and cemented
on to the top of the rod, and e is the electric conductor secured to the cap by
binding, or it may be that the wire may be passed through a hole or slot in the end
of the insulating rod as represented in Figure 8 instead of being held by a cap
fixed on the rod.
Figures 4 and 5 show a modification, the lower end of the rod c being inserted.
into a socket formed to receive it in the arm a. The rod may under certain
circumstances be hung from the fixing on the pole as is shown by Figures 6, 7
and 8 the wire being passed through or hung by means of a cap from its lower
end.
If these insulating rods are made of sufficient length they form a very certain
means of insulating an overhead conductor, as there is no metal inside the rod as
in the case of insulators cemented on to an iron bolt, and the rod cannot therefore.

page_text: be pierced by a current. The only way in which its insulation can suffer is by
surface leakage.
In most cases it is found desirable as is indicated in Figures 9, 10, 11 and 12 to
cement or fasten by means of an insulating material, glass or porcelain washers or
washers of other insulating material on to the rod with a small interval between
each, the surface is then enormously increased between the ends of the rod. In
fact the current would then have to leak over a great many feet of surface before
it could get to earth or to the other conductor. These rods may be so formed
that they may be hung from the poles or stood in sockets so as to be easily removed
when they may be cleaned by immersing in hot oil or other dissolving fluid, and
also if found desirable dipped in some form of parafine, wax, oil or other insulating
substance, which will leave them with a surface which will prevent moisture
depositing upon them for a considerable period, and thus improve the insulating
quality of the surface.
Two or three rods may be grouped together as is indicated by the Figures 13
and 14 so as to give greater strength to the insulating support for the wires. The
discs which are threaded on to the rods may have their outer edges turned up a
little as seen in Figure 15 so as to admit of each one forming a shallow oil cup.
These rods may ha moulded with the diene or roinntions non thom in
Figure 16 but a better quality of article is obtained by making the insulators
composite. One method of putting on the discs is indicated by Figure 17; it is to
thread them on to the rods with rubber or other flexible washers in between them,.
and then tighten up from each end so as to make the flexible washer make a good
contact between the rod and the various washers. An adhesive and insulating
substance such as pitch may also be used in the process.
Another means of efficiently suspending the high pressure conductors is to carry
them from the pole on a long length of cord of silk manilla or other flexible
insulating material. The cord may also be prolonged for a corresponding length
below the wire and held tight in order to prevent the wires swinging about. These
cords are made of sufficient length to give the necessary insulation. In Figure 18
findicates the post. gg wires or electric conductors and hh the fibrous cords. I
prefer to soak these cords in an insulating oil such as petroleum oil or wax in order
to make them as far as possible waterproof, and to confine moisture to their surface
and to prevent it entering into the body of the cord.
In order to maintain them in an oily condition they may terminate in oil cups at
each end. This arrangement is shown in Figure 19 are the upper and lower
oil cups and there may also be an oil cup 3 on the cable fastening where the upper
and lower cords are attached. The cords will thus act as wicks, and keep them-
selves fully saturated with oil, which will of course help to maintain their insulating
qualities.
In some cases where insulating rods are used I cover their surface with a thin
coating of fibrous material and saturate this by preference with insulating oil or
In Figure 20 k is a jacket of fibrous material around the porcelain or glass.
rod and is an oil cup into which it dips.
wax.
Where alternating currents are used I find that if a little moisture is deposited
upon the surface of an insulator and the distance between the points of high E.M.F.
is sufficiently great, that enough current will be conducted by the moisture to dry
it up, and so render the insulator perfect.
Where the surface is solid porcelain or other insulator with a smooth surface
the result of moisture is generally the formation of an arc, or there is a sufficient
amount of moisture deposited to form a permanently bad insulation. Now I avail
myself of these facts in the above system. The suspending cords and also the
fibrous material on the surface of the insulators in the first place do not get much
moisture deposited on their surfaces. In the second place what is deposited is
evenly distributed, and thus in times of damp or wet weather a small amount of
current flows and maintains the insulation of the insulators in very perfect
condition.

page_text: With both these systems, as also with the plan of insulators as ordinarily used,
I prefer to enclose the insulators, and in fact to cover in the space around the pole
which carries the insulators with a small house or box, with holes of considerable
size in relation to the diameter of the line wire for it to pass through. These holes
may be sheltered against rain and moisture blowing in by means of baffle plates at
a short distance inside and outside the box.
In Figures 21 and 22 m is the house or box, m¹ the openings for the passage of
the conductors and n n are baffle plates fixed upon the conductors. Figure 23
shows a similar arrangement but with the conductors suspended and insulated by
cords. The holes in the box may also be fitted with insulating tubes as seen in
Figure 24 and also have baffle plates as before. The tubes marked o may be
made in porcelain; they are fixed in diaphragms which serve to close the ends of
the box. By this means a box is obtained which although the insulator is thoroughly
in contact with the air prevents the deposition of a great deal of dirt and moisture
upon the insulators or cords which carry the wires, and thus maintains their insula-
tion in very much better condition than it would otherwise be. Figure 25 shows
another form; in this case the box p consists of a cylinder with conical arms on
either side of it. The conductor passes concentrically through holes in the
cylindrical part of the box; these holes are sheltered by baffle plates. The con-
ductor is suspended by insulating cords q with oil cups. The box can either be
hung from a support above it or it may be fixed to a post or posts in any convenient
way. In some cases as illustrated by Figures 27 and 28 the holes in the box are
nearly covered by a diaphragm of thin fibrous material such as oil skin, but this,
as also nearly covering the holes with any other form of insulator, has a certain
disadvantage that under certain circumstances sparks will continuously jump from
the wires on to these insulators, which can only be considered as partial insulators.
In practice the size to make these holes for the wires entering, and the extent of
covering up of these holes with screens will be found for each particular case and
climate.
In cases where the roads or country along which the conductors pass is much
frequented, or where danger from the wires is anticipated I adopt an arrangement
analogous to that in concentric cables and represented diagrammatically by
Figure 29. I insulate one of the conductors marked s as above explained on either
specially good insulators or suspended in a fixed position by means of insulating
cords round which as I have explained I prefer to put a protecting box or covering.
This lead or conductor s represents the central conductor in a concentric cable and
the outside conductors of the concentric cables I replace by wires ttt stretched
from pole to pole upon insulators placed round about the central conductor and
central insulator. These outside or return conductors can be placed outside the
projecting box. It is desirable to make the return conductor t in as many wires as
possible, so as to make as complete a network round about the insulated or outgoing
conductors as possible. These external conductors I connect to earth either at
several places or at one place along the line, preferably at the dynamo end, and so
the potential upon them can never be greater than that due to the copper loss upon
the line. Figure 30 shows more in detail a suitable arrangement. The insulator
carrying the conductor s is within a wooden barrel arranged as already described.
The wires tt are fixed on the exterior of the barrel and the barrel has arms uu
which are supported by porcelain or glass insulators v fixed upon posts w. These
external conductors may be threaded through rings every few yards as in Figure 31
in order to keep them in as nearly as possible a circular forin and they may also
as already described be held on rings at the posts which rings are carried on
insulators.
The conductors may also as in Figure 32 be so arranged that they form an open
spiral round about the outgoing conductor, by this means it is impossible to get at
the inner conductor without breaking or going between the outside or earth
conductors. Also if the central conductor falls it will be immediately short-
circuited, on the outer ones, and thus prevent its doing any damage.

page_text: When transmitting currents of high tension through long electric mains it
frequently happens that certain parts of the circuit and apparatus are charged to
a pressure considerably in excess of the maximum working pressure.
In order to overcome this difficulty I adopt an arrangement which is shown
diagrammatically by Figure 33. I place non inductive resistances marked A of
suitable form and dimensions across the poles of the dynamo B across the poles of
the transformers C C and across the mains DD at various places. I may also
connect the same to earth by such means.
The non-inductive resistance may be made of very fine wire or material of high
resistance. They may be made of strings or wicks kept moist with water so as to
be of very high resistance, and to dissipate a very small quantity of current only.
Figure 34 indicates a thin string wound upon a frame; it is kept moist by water
which is allowed to find its way along it. Figure 35 shows wicks hung over rods
and dipping into vessels containing water. Or as is represented in Figure 36 the
non-inductive resistances may be made of a number of cells of water in series with
electrodes dipping into each cell. Or as in Figure 37 they may consist of long
tubes filled with water and being of sufficient section to conduct any desired amount
of current. The object to be sought after being that they should have as little
self-induction as possible.
Moreover the liquid resistances are desirable from the point of view that a
momentary rush of current can take place through them more easily. Their
resistance only coming up after a current has flowed for some little time.
These resistances will form as nearly as possible a non-inductive path through
which any extra or charge currents may be with facility discharged, and so prevent
the critical state which gives rise to charge currents appearing upon and damaging
apparatus used in the system.
These discharges may also be used as lightning arresters for continuously con-
ducting away and transmitting to earth any electrical charge, rather than letting
it accumulate until it has reached a sufficient E.M.F. to break down the insulation
of the system.
In some cases it is desirable to use as indicated in Figure 38 a number of these
dischargers marked E as well as and forming one circuit in scries with an air gap
at F between points or electrodes set at a distance which is just too great for the
ordinary E.M.F. to spark across. When the charge current gets to sufficient
pressure to escape it will do so across the air space provided rather than break
down the insulation of the system, but no great quantity of current will flow. The
arc will go out on account of the high resistance of the cells in series with it there
not being sufficient quantity of current for the arc to maintain.
Figure 39 indicates a combination of non-inductive resistances and air gaps
forming outlets between electric mains fed by a dynamo and the earth.
These discharge points may have a blast of air between them, or may have a
fan working to help the blowing out of the arc. This arrangement is illustrated
by Figure 40 where F F are the discharge points, G a fan and H is a nozzle by
which the air issues producing a strong current between the surfaces F F.
In some cases I prefer to make the discharge points as in Figure 41 in such a
way that one of them consists of a conducting point nearly touching or at a
moderate distance above a dish of water which is in connection with the other
pole. In some cases as in Figure 42 a second point may project up through the
water or liquid to near the surface, or as in Figure 43 several points may be used
above the surface of the water, in this way any very small quantity of current from
high tension will easily jump to the water and so be discharged, but no current of
any quantity will be able to follow this up. Non-inductive resistance may also be
arranged in series.
This apparatus may be used as a high pressure discharger or as a lightning
protector.
In some cases as in Figure 44 I make dischargers or lightning protectors of
two points or two tubes closely facing each other, and across which the dynamo

page_text: current will not jump. In the figure K is a pipe receiving the air from the fan
and also connected with one of the electric mains or terminals. L is a plug con-
nected with the other terminal and impeding the air issuing from the pipe. When
a lightning or other discharge takes place, rather than hurt the apparatus it will
jump across this air space, and be immediately blown out by the strong blast
emerging from the tube or across the points, produced by the fan or blower.
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 :-
1. Insulators substantially as described consisting of a porcelain or glass rod
held in a socket or clamp at its lower end and at its upper end supporting the
conductor with or without the intervention of a cap.
2. Insulators substantially as described consisting of a porcelain or glass rod
held at its upper end in a socket or clamp hung from a supporting arm and at its
lower end carrying the conductor with or without the intervention of a cap.
3. Insulators substantially as described consisting of a porcelain or glass rod
suitably held or suspended and supporting the electric conductor and having discs
or projections of like material threaded or moulded upon them.
4. Insulators substantially as described consisting of two or more porcelain or
: glass rods held in a socket or clamp at their lower ends and at their upper ends
furnished with a cap upon which the conductor is supported.
5. Insulators substantially as described consisting of a porcelain or glass rod
- suitably held or suspended and supporting the electric conductor and having discs
or projections of like material and also compressible washers threaded upon it and
tightened up from the end by a screw and nut or its equivalent.
6. Insulators substantially as described consisting of fibrous cords suspending the
-electric conductors and oil cups supplying insulating oil to saturate the cords and
keep them free from moisture.
7. Insulators substantially as described consisting of fibrous cords suspending the
electric conductors, and enclosed and protected by a housing surrounding the cord
and the conductor, and with holes for the free passage of the conductor.
8. Insulators substantially as described and consisting of a porcelain or glass
rod suitably held or suspended, and supporting the electric conductor, and a jacket
of fibrous material surrounding the rod and dipping into an oil cup.
9. An insulator supporting an electric wire or conductor enclosed substantially
as described in a box with holes in the ends of the box for the passage of the wire
or conductor and with or without baffle plates to shelter the holes.
10. An insulator supporting an electric wire or conductor enclosed substantially
as described in a box with holes in the ends of the box and tubes of insulating
material fitted into the holes.
11. An insulator supporting an electric wire or conductor enclosed substantially
as described in a box with diaphragms of insulating material such as oil skin at
the ends and with holes in the diaphragms for the passage of the wire or
-conductor.
12. The arrangement of a high tension electric circuit substantially as described
the high tension wire or conductor being surrounded with a number of other wires
separated from it by an air space and serving to complete the circuit and which
are maintained at as low a tension as may be requisite for safety.
13. Aerial concentric conductors consisting of central and surrounding wires
supported on insulators with an air space between the centre wire and the outer
wires which constitute the return conductor.
14. In aerial concentric conductors in which the outer conductors form a cage or
network round the inner conductors, connecting the outer conductors to earth so as
to bring down their potential to that of the earth.
15. In aerial concentric conductors in which the outer conductors form a cage or
network round the inner conductors connecting the outer conductors to earth at

page_text: one point so as to bring down the potential of the conductors at that point to that
of the earth without a shunt flow of current through the earth.
16. The arrangement substantially as described of high tension conductors
suspended in the air in such a way that the lead if it should break and fall is
caught by the return or earth conductor.
17. The arrangement substantially as described of high tension electric con-
ductors so that the lead or insulated conductor is protected by a cage of return
conductors against being touched as by falling or swinging wires.
18. The combination substantially as described with high tension dynamo circuits.
of non-inductive resistances in such manner as to admit of the escape of current.
when shocks of excessive pressure from any cause occur.
19. The combination substantially as described with high tension or dynamo
circuits of non-inductive resistances in combination with air gaps in such manner
as to admit of the escape of current when shocks of excessive pressure from any
cause occur.
20. The combination substantially as described with high tension or dynamo
circuits of an air gap traversed by a blast of air driven by a fan in such manner
as to admit of the escape of current without risk of establishing an arc when
shocks of excessive pressure occur.
21. The combination substantially as described with high tension or dynamo
circuits of a point and water dish arranged in such manner as to admit of the
escape of current when shocks of excessive pressure occur.
Dated this 17th day of November 1892
S. Z. DE FERRANTI.