Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
SPRING LOADED GROUND CLAMP
Technical Field
This invention relates to the field of clamping devices that removably clamp a
ground cable onto an electrical conductor, and in particular to a ground clamp
that releasably clamps onto an electrical conductor using only a fixed jaw and
a
high compression spring-loaded movable jaw, wherein the spring loaded jaw
cannot be manually retracted away from the fixed jaw without the use of a
customized hot stick, made to provide a lineman with a significant mechanical
advantage so as to be able to retract the movable jaw from the fixed jaw.
Background
Electrical workers use grounding cables regularly in the industry to handle
dangerous voltage and current hazard on de-energized power lines and
electrical
equipment. Grounds are designed to be installed and removed using a long
insulating tool, referred to herein as a hot stick, to keep the worker at a
safe
distance from the hazard.
When installing grounds, the first connection is always made to a ground or
earth
point. Workers will normally make this connection by hand instead of with the
insulated hot stick, as there is no hazardous energy when making this
connection.
Any time a connection is made to an electrical conductor or apparatus that
could
be at a different electrical potential from ground, this connection must be
made
using an insulating tool. This is especially true in a high voltage
environment (for
example, over 69 kV). Due to the design of conventional ground clamps, they
can
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be installed and removed by hand instead of being installed using an
insulating
tool. It is not uncommon in applicant's experience for workers to make the
mistake of installing a ground clamp on a conductor, or removing one from a
conductor by hand instead of with an insulating tool. This potentially exposes
the
worker to a voltage and current potential and consequently may result in
electrocution of the worker. To applicant's knowledge, this has accounted for
fatalities and electrocution incidents in the industry.
Consequently, there is a need in the industry for a ground clamp that operates
in
combination with an insulating tool so as to prevent the worker or lineman
from
3.0 being able to operate the ground clamp without the use of the
insulating tool.
This is to inhibit workers or linemen from attempting to install or remove the
ground clamp by hand. To accomplish this a lock out mechanism in the form of a
strong spring having a large spring force is described below which prevents
manual operation of the ground clamp as the ground clamp can only be actuated
or un-locked with the customised insulating tool.
Summary
A grounding clamp system according to the present disclosure includes a first
jaw
and a second jaw in opposed facing relation to the first jaw so as to define a
gap
therebetween. The first jaw is a piston mounted movable jaw. The piston is
slidably mounted in a housing. A first end of the piston is mounted to the
first
movable jaw. The housing is coupled to the second fixed jaw by a rigid frame
so
as to maintain the first and second jaws in their opposed facing relation. A
spring
is mounted in the housing and is coupled to the piston to resiliently urge the
piston and the first jaw towards the second jaw so as to resiliently close the
gap
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between the first and second jaws. The spring has a spring force in the range
of
150 to 250 pounds force required to fully compress the spring.
A hot stick connector, such as an eye mounted to the second end of the piston,
extends from the second end of the piston. The second end of the piston is
opposite the first end of the piston.
The system includes an insulated hot stick having a hook retractably mounted
in a
first end thereof. A tensioning rod linkage is coupled to the hook at one end
of
the rod linkage, and coupled at the other end of the tensioning rod linkage to
a
lever arm. The lever arm is pivotally mounted on the hot stick, on handle end
of
the hot stick. The handle end of the hot stick is opposite the first end of
the hot
stick. The other end of the tensioning rod linkage is mounted to the lever arm
at
a mechanical advantage distance along the lever arm away from the hot stick.
The first end of the hot stick is adapted to have the housing seat thereon
when
the hook is engaged with the hot stick connector eye and the hook retracted to
a
first retracted position by rotation of the lever arm in a first direction so
as to
tension the tensioning rod linkage. In the first retracted position the hook
pulls on
the connector to seat the ground clamp housing onto the first end of the hot
stick. Continued and increasing tension on the tensioning rod linkage by
further
rotation of the lever arm in the first direction away from the first end of
the hot
stick and towards the second end of the hot stick retracts the hook to a
second
retracted position wherein the piston, for example a flange on the piston,
compresses the spring against the return biasing spring force of the spring so
as to
retract the first jaw away from the second jaw to thereby open the gap so as
to
allow entry or exit of a conductor into the gap between the jaws.
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When the lever arm is rotated in a second direction opposite to the first
direction,
the return biasing spring force of the spring urges the first jaw towards the
second jaw to thereby at least partly close the gap. This engages the jaws
with a
conductor positioned in the gap. The heavy or strong spring force keeps the
ground clamp jaws tightly clamped on the conductor.
The lever arm is rotated in the first direction to open the gap between the
first
and second jaws. The lever arm rotated in the second direction to at least
partly
close the gap so as to clamp a conductor between the first and second jaws.
Advantageously the tensioning rod linkage is pivotally mounted to the lever
arm.
3.0 Further advantageously the tensioning rod linkage includes first and
second linear
rods, wherein the first linear rod is coupled at a first end thereof to the
hook and
is slidably mounted to the first end of the hot stick so as to translate
linearly along
and parallel to the first end of the hot stick, and wherein the first linear
rod is
pivotally coupled at a second end thereof, opposite the first end of the first
linear
rod, to a first end of the second linear rod. The second end of the second
linear
rod, being pivotally mounted to the lever arm, is pivotable relative to the
first
linear rod so as to form a small included angle between the second linear rod
and
the hot stick as the lever arm is rotated to open and close the first and
second
jaws.
Yet further advantageously, the lever arm is an over-center lever arm
releasably
lockable into an over-center position when fully rotated in the first
direction until
a handle end of the lever arm is flush against the handle end of the hot
stick.
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Brief Description of the Drawings
FIG. 1 is a side elevation view of a ground clamp according to the present
specification.
FIG. 2 is a section view along line 2-2 in FIG. 1.
.. FIG. 3 is, in perspective view, the ground clamp of FIG. 1 mounted on the
end of a
customised hot stick with a ground clamp tensioning assembly according to the
present specification, with the jaws of the clamp open.
FIG. 4 is the spring loaded ground clamp system of FIG. 3 in front elevation
view.
FIG. 5 is the spring loaded ground clamp system of FIG. 4 in side elevation
view.
3.0 FIG. 6 is the spring loaded ground clamp system of FIG. 5, with the
jaws of the
clamp closed.
FIG. 7 is a section view along line 7-7 showing the ground clamp in its open
position with spring completely compressed in FIG. 5.
FIG. 8 is the section view of FIG. 7 showing the jaws of the clamp closed with
the
.. spring uncompressed, and showing an alternative embodiment of the hook and
hook shank wherein the hook is pivotally mounted on the shank.
FIG. 9 is, in partially cutaway view, the ground clamp of FIG. 1 with the
clamp jaws
clamping a conductor having a maximum diameter that can be accommodated in
the illustrated embodiment.
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FIG. 10 is the view of FIG. 9 with the clamp jaws partly closed so as to clamp
a
slightly smaller diameter conductor.
FIG. 11 is the view of FIG. 10 with the clamp jaws closed to accommodate a
small
diameter conductor.
FIG. 12 is, in perspective view, the hot stick of the system shown in FIG. 3.
FIG. 13 is, in side elevation view, the hot stick and tensioning assembly of
FIG. 12,
with the hot stick head removed.
FIG. 14 is the view of FIG. 13 showing the tensioning assembly on the hot
stick in
its partly tensioned position with the hot stick head removed.
FIG. 15 is an enlarged perspective view of the lever arm and tensioning rod
linkage of the tensioning assembly in its partly tensioned position.
Detailed Description
As seen in the accompanying illustrations wherein like part numbers represent
corresponding parts in each view, the present disclosure is a spring loaded
grounding clamp system which employs a strong spring as a safety lockout for
the
ground clamp.
The system includes a ground clamp 12 which, when connected to and seated on,
the hook end of a hot stick 14, provides for electrically insulated remote
operation of a spring loaded ground clamp by a lineman holding the hot stick
and
pulling on, or releasing, a lever arm on the hot stick. The system provides
increased safety for the lineman as the heavy, in the sense of having a strong
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spring force, spring providing the spring loading of the clamp has a high
spring
force to overcome; the object being that the lineman is forced to use the hot
stick
tool in order to overcome the spring's spring force and cannot usefully
operate
the spring loaded ground clamp manually without the hot stick tool.
Thus as seen in FIGS. 1 and 2, ground clamp 12 includes a first movable jaw 16
and a second fixed jaw 18. The first and second jaws 16 and 18 are in opposed
facing relation so as to define a conductor-receiving gap 20 therebetween.
Spring
housing 22 contains a piston 24 slidably journaled therethrough for
translation of
the piston in direction A. An upper end 24a of piston 24 is mounted to the
3.0 underside of the first jaw 16 so as to also translate first jaw 16 in
direction A.
Spring housing 22 is coupled to the second jaw 18 by a rigid frame 26 so as to
maintain the first and second jaws in their opposed facing relation oppositely
disposed about gap 20.
Spring 28 is mounted in the spring housing 22. Flange 30 is mounted to piston
24
within housing 22 so as to couple piston 24 onto spring 28. Spring 28 presses
against flange 30 so as to resiliently urge piston 24 and first jaw 16 towards
the
second jaw 18. Translation of first jaw 16 towards second jaw 18 at least
partially
closes the gap 20 so as to clamp a conductor 32 between the jaws thereby
forming an electrical connection between the ground clamp and the conductor.
Advantageously spring 28 is a helical coil spring having a strong, preferably
linear,
spring force, for example in the range of 150 to 250 pounds force required to
fully
compress the spring.
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The spring force is selected so as to balance two competing human factors. To
applicant's knowledge a lineman, using both of his hands, would be hard
pressed
to continuously pull a tension force between his hands of no more than
approximately 150 pounds force.
Keeping in mind that, in the present
application, if a lineman was capable of that pulling force, it would in
applicant's
view still be very difficult for the lineman to translate that strength into
compressing the spring 28 in the ground clamp so as to open the clamp's jaws
16
and 18, and then operating the ground clamp described herein in which the
spring 28 has a spring force in full compression of at least 150 pounds force,
3.0 without the assistance of the hot stick 14 also described herein.
Without the use
of the hot stick 14, the lineman would have to hold the ground clamp 12 in one
hand, for example by grasping the ground clamp frame 26 which holds the two
jaws in their alignment and hold the ground clamp-to-hot stick connector (for
example the eye 34 extending from the lower end 24b of the piston 24 in the
illustrated examples) in the other hand, and while pulling the two apart
manually
so as to open the jaws. Then, without releasing the tension, the lineman would
have to reach out, for example from the bucket truck in which the lineman is
standing and hook the open jaws of the ground clamp 12 over the conductor 32.
Applicant is of the view that the lineman would if given the choice take the
easier
(and also safer) route and use the hot stick 14 with the tensioning assembly
described herein.
Another human factor that applicant has taken into consideration in the design
of
the present ground clamp system, is the force that a lineman can exert on the
lever arm 36 mounted on hot stick 14 when compressing the spring 28 in the
.. ground clamp 12. Given the mechanical advantage provided by the lever arm
36,
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a lineman must still be able to fully compress the spring in the ground clamp
using
the tensioning assembly on the hot stick, which may become difficult where the
spring has a very high spring force at full compression. Hence there will be
an
upper limit on the spring strength of the spring, above which a lineman may
struggle to operate the tensioning assembly.
There will also be an upper limit on the spring strength of the spring, above
which
the lever arm 36 and tensioning rod linkage 38 may not withstand after
repeated
operation of the tensioning assembly, without the lever arm and linkage having
to
be heavy in order to be sufficiently strong. If the lever arm and tensioning
linkage
3.0 are overly rugged and heavy, the hot stick may become cumbersome. In
applicant's opinion, a heavy and cumbersome hot stick is less likely to be
used by
a lineman than one that is relatively light and thus more easily used. The
design
factor to be considered then becomes whether a relatively lightweight lever
arm
36 and associated tensioning rod linkage 38 will withstand the repeated force
necessary to repeatedly fully compress the spring 28 in the ground clamp 12
when fully opening the clamp's jaws 16 and 18. In the illustrated example in
FIGS.
3-7, it takes approximately 160 pounds force to fully compress spring 28.
The lever arm 36 provides a mechanical advantage to the lineman. This allows
the
lineman to pull the required compression force on the ground clamp spring 28
via
the lever arm 36 and tensioning rod linkage 38 to open the jaws 16 and 18
while
using only one hand to pull on the lever arm 36 all the way to the locked over
center position, and then manipulating the hot stick 14 with the both hands.
As
seen by way of example in the illustrations, for example FIGS. 6, and 12-14,
the
mechanical advantage may in one embodiment be in the range of approximately
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3:1 to 4:1. The approximate range of mechanical advantage may be seen by
comparing in the figures the distance D1 (shown in FIG. 6) between the lever
arm
hinge 40 (where the lever arm 36 is pivotally mounted to hot stick 14), and
the
handle end 36a of lever arm 36, to the distance D2 between the lever arm hinge
40 and the pivoting connection (pinned hinge 42) where the rod linkage 38 is
joined to lever arm 36 by an adjustable threaded connection between 38a and
46.
Distance D2 is alternatively referred to herein as the mechanical advantage
distance of the lever arm.
Thus, by way of example, if the required compression force to fully compress
3.0 spring 28 is 160 pounds force, then, using lever arm 36, the lineman would
have
to pull in direction B on lever arm handle end 36a using approximately 40
pounds
force if the mechanical advantage is approximately 4:1.
Using the same
mechanical advantage ratio of 4:1, if the spring force of spring 28 at full
compression is 240 pounds force, then the lineman would have to pull on lever
arm 36 with 60 pounds force. If the mechanical advantage ratio is only 3:1,
then
in the latter example, the lineman would have to pull on the lever arm with 80
pounds force, which in applicant's opinion is likely the upper limit, and
possibly
more than the upper limit, of what a lineman may possibly be able to achieve.
Advantageously, as illustrated, lever arm 36 may be mounted on hot stick 14
using a collar or sleeve 44, wherein the lever arm hinge 40 is mounted onto
sleeve
44, for example midway along its length. The length of sleeve 44 assists in
distributing the load on hinge 40 to hot stick 14 during rotation of the lever
arm in
direction C in order to open the ground clamp's jaws 16 and 18. Lever arm
hinge
40 is elevated off sleeve 44 by a small distance, sufficient to provide for
over-
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center locking of lever arm 36 against hot stick 14 once lever arm 36 has been
fully rotated in direction C. The length of rod linkage 38 is adjustable so
that
spring 28 is fully compressed as lever arm 36 comes to it's fully rotated over
center and locked position parallel to hot stick 14 upon completion of full
rotation
in direction C. Preferably, as lever arm 36 is rotating about hinge 40 into
it's over-
center position flush along hot stick 14, a small force component from the
tension
on the tensioning rod linkage 38 urges lever arm 36 against hot stick 14. This
retention force may for example be in the order of five pounds force. Thus, in
that example, the lineman would have only to exert five pounds force pulling
3.0 lever arm 36 away from hot stick 14 in order to release lever arm 36
from its over-
center locked position closing the ground clamp.
As seen in FIG. 15, in the illustrated embodiment, not intended to be
limiting,
lever arm hinge 40 is mounted to, so as to be raised off, sleeve 44, on a pair
of
parallel mounting ears 43. Parallel fork arms 36b on lever arm 36 extend from
the
handle end 36a to lever arm hinge 40, where the ends of fork arms 36b are
pinned to their corresponding mounting ears 43 for rotation of lever arm 36 in
direction C so as to rotate lever arm 36 relative to sleeve 44 and hot stick
14.
Tensioning rod linkage 38 includes a planar threaded member 38a rotationally
coupled at one end to pinned hinge 42 on fork arms 36b, and at the other end
to
a length adjustment coupling member 46. Length adjustment coupling member
46 may be mounted in threaded engagement to planar member 38a, or may be
threaded at both female ends of member 46 in the manner of a turnbuckle, so as
to allow selective lengthening or shortening of tensioning rod linkage 38. As
lever
arm 36 is rotated in direction C into its over-center locking position flush
along
hot stick 14, planar member 38a is nested between fork arms 36b and mounting
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ears 43 so as to allow tensioning rod linkage 38 to also lie flush along hot
stick 14.
When lever arm is unlocked from it's over-center locked position by being
rotated
in a direction opposite to direction C, a small pulling force is required, for
example
approximately five pounds force, to provide the moment required to break open
the over-center locking. As the rotation of lever arm 36 then continues,
tensioning rod linkage moves in direction D thereby releasing the tension
holding
spring 28 compressed closing ground clamp. Spring 28 then urges piston 24 and
first jaw 16 towards second jaw 18, at least partly closing gap 20, and
clamping a
conductor 32 located in the gap between the jaws 16 and 18 with the return
3.0 spring force of spring 28. Preferably, spring 28 is substantially
linear so that
spring force is almost the same through all or substantially all of its full
range of
motion, that is from uncompressed to fully compressed.
Tensioning rod linkage 38 further includes at least a long, primary linkage
member, or tie rod 38b, which may be an electrically insulated flexible rod
such as
made of fiberglass so as to be relatively light weight yet strong in tension.
The
length of tie rod 38b will depend on the length of hot stick 14. The longer
the hot
stick, the longer tie rod 38b. In the illustrated embodiment, tie rod 38b
extends
from coupling member 46 to a hook rod 48. Tie rod 38b is pivotally coupled to
hook rod 48 by pinned hinge 52. Pinned hinge 52 allows rotation of tie rod 38b
in
direction E relative to hook rod 48. Hook rod 48 is slidably mounted in a
longitudinally extending channel 50a in hot stick head 50 for translation of
hook
rod 48 along the hook end 14a of hot stick 14, parallel and snugly adjacent to
hook end 14a of hot stick 14. The channel 50a in head 50 maintains hook rod 48
parallel to hot stick 14 during it's translation along the hook end 14a.
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Tie rod 38b does not however remain parallel to hot stick 14 as lever arm 36
is
rotated. As lever arm 36 is rotated about lever arm hinge 40, pinned hinge 42
is
correspondingly rotated through an arc about hinge 40. Because tie rod 38b is
coupled to pinned hinge 42 via members 38a and 46, rotation of pinned hinge 42
in an arc swings tie rod 38b in direction E about pinned hinge 52, and
correspondingly through a small included angle F formed between tie rod 38b
and
hot stick 14. The shorter the length of hot stick 14, the slightly greater the
included angle F, and conversely the longer the length of hot stick 14, the
slightly
smaller the included angle F.
A hook 54 is mounted onto the end of hook rod 48 opposite to pinned hinge 52.
The shank 54a of hook 54 is rigidly co-linear with hook rod 48, and is free to
slide
along the channel 50a in head 50 in which hook rod 48 is slidably mounted.
Thus
hook 54 is retractably mounted on the hook end 14a of hot stick 14. As
tensioning
rod linkage 38 is thus coupled to hook 54, rotation of lever arm 36 in
direction C
retracts hook 54 to or into the distal end 50b of head 50 on hot stick 14.
The hook end 14a of hot stick 14, and in particular head 50 is adapted to have
spring housing 22 seat onto the end of head 50 when 54 hook is engaged with
eye
34 and the hook retracted to a first retracted position by rotation of the
lever arm
in direction C so as to tension the tensioning rod linkage. A hollow guard
having a
bulbous cavity may optionally be mounted to the underside of the spring
housing
22 so as to cover eye 34 while allowing insertion of hook 54 and the end of
head
50 into the guard cavity so that a lineman may engage hook 54 with eye 34
inside
the guard. The guard is intended to inhibit a lineman from attempting to use a
shortcut to overcome spring 28 such as by inserting a hand held lever or
handle
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device, for example a screwdriver, through eye 34 so as to provide the lineman
with greater purchase to pull down on piston 24 with increased force.
In the first retracted position the hook 54 pulls on the eye 34 to seat the
spring
housing 22 onto head 50 at the first end of the hot stick. Continued and
increasing tension on the tensioning rod linkage 38 by further rotation of
lever
arm 36 in direction C (away from the first end of the hot stick and towards
the
second, opposite, end of the hot stick) retracts the hook 54 to a second
retracted
position wherein the flange 30 on piston 24 compresses the spring 28 against
it's
return biasing spring force so as to retract the first jaw 16 away from the
second
3.0 jaw 18 to thereby open the gap 20 so as to accept a conductor 32
therein.
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