When having to carry out operations of maintenance or repair on an overhead electric line, the rules in force (CEI-EN 61239) provide for the use of two grounding and/or shorting devices on the stretch of the line involved in the operation, from which the voltage has already been previously removed so as to create a safety zone apt to guarantee protection to the operators from any possible accidental voltage returns.

At present, the grounding and shorting devices comprise three pliers of conductive material, electrically connected one to the other and/or to the ground, each apt to tighten around one of the cable conductors of the electric line. In the devices used at present, the pliers work similarly to a chisel, that is, they are opened and set up for operation, and they snap shut when the conductor hits an unlocking lever. Such devices also include a coupling unit, with a control rod to position the grounding pliers on the overhead electric line, the release of the coupling unit from the pliers being obtained by simply imparting a tractive force onto elastic locking means.

Due to the increase of the estimated short-circuit currents and to the introduction of devices to remove the oxides developing on the surfaces of the bare cable conductors, the grounding and shorting device is at present usually gauged so as to generate, in operation, a very high tightening force on snapping of the pliers. This leads to the serious drawback of damaging the bare cable conductors, especially if narrow sized.

The object of the present invention is to supply a grounding and shorting pliers device apt to reduce the unfavourable stresses on the bare cable conductors, by adopting an improved system to clamp such conductors and release the coupling unit, which makes use of the tractive

force to insert the bare cable conductor into the pliers, while a mechanical consenting device, depending on the correct working position of the conductor into said pliers, provides to release the coupling unit.

According to a first essential aspect of the present invention, the grounding and shorting pliers device for bare cable conductors is characterized in that, each of the pliers-comprising a body and a movable jaw formed by two articulated portions, the first portion being pivoted on said body and being urged into a closing position towards said body by spring means-is equipped with an oscillating lever apt to engage the coupling unit of the device, said lever comprising at one end a tooth caused to cooperate with the head of a pin of said coupling unit by a release spring carried by an extension of said lever, while the other end of said lever is arranged so as to be engaged by the bare cable conductor inserted into the pliers between said body and the second articulated portion of said movable jaw, in order to cause the release of the coupling unit only at the moment in which the position of the conductor into the pliers corresponds to the correct working position.

Suitably, the second portion of said movable jaw is articulated to the first portion by means of a pivot, with possibility to perform oscillations limited by stops, and the bare cable conductor engages said second portion, in its working position, beyond said pivot, towards the first portion of the jaw.

According to another aspect of the present invention, said release spring merely acts on the head of the pin of the coupling unit.

According to a further aspect of the present invention, the portions of the grounding and shorting pliers of the device, between which is inserted the bare cable conductor, are knurled or indented so as to remove the oxides from said conductor.

The invention will now be described in further detail, with reference to a preferred embodiment thereof, illustrated by way of example on the accompanying drawings, in which:

Fig. 1 is a diagrammatic view of the grounding and shorting pliers of the device, according to a preferred embodiment of the invention, ready to be hoisted on the overhead electric line with a coupling unit and the respective control rod; and Figs. 2 and 3 are similar section views of the same pliers, illustrating their operating conditions in an intermediate position and, respectively, in a working position of the pliers.

As shown in fig. 1, each of the grounding and shorting pliers forming part of the device according to the invention comprises a body 1, onto which there is pivoted in 2 a movable clamping jaw 3, consisting of two portions 3A and 3B articulated by means of a pivot 3C. The movement of the jaw 3 is controlled by spring means consisting of a cylindrical spiral spring 4, ajustable by means of a screw 4A around which it winds. An L- shaped engagement lever 5 is mounted, oscillating about a pivot 6, into the body 1 of the pliers. To an extension 5A of said lever 5 there is associated a release spring 7, arranged into a seat 8 housing the pin 9 and the head 10 of the coupling unit 11, which-usually by making use of a suitable hooking control rod-allows to hoist the grounding and shorting device onto the overhead electric line. The body 1 is also provided with a ring 12, which helps to recover said body at the end of the maintenance operations on the electric line, and with a nut 13 to connect the shorting and/or grounding cables. The portion 3B of the jaw 3 is apt to perform limited oscillations about the pivot 3C, in respect of the portion 3A of said jaw, projections (not shown)-acting as stops-being provided on either one of said jaw portions.

When the device is in the condition illustrated in fig. 1-namely the condition of rest, previous to use-the head 10 of the pin 9 of the coupling unit 11 cooperates with a tooth 15 formed at one end 14 of the oscillating lever 5, and is pressed by the release spring 7 into engagement with said tooth 15. In this condition, the movable camping jaw 3 is in contact with

the body 1 with its portion 3A and the length of the portion 3B pivoted thereto.

Figs. 2 and 3 show two successive working steps of the grounding and shorting pliers of the device, as it starts to operate. When the pliers are positioned onto the bare cable conductor 16, this latter causes the opening of the jaw 3, engaging its portion 3B against the action of the spring 4 (fig.

2); the conductor 16 thus gradually inserts itself between the body 1 of the pliers and the portion 3B of the clamping jaw 3. The portion 3B of said jaw 3 is thereby gradually parted from the body 1, oscillating clockwise about the pivot 3C so as to properly house the conductor 16, which is guided between the body 1 and the camping jaw 3 (fig. 2) thanks to the mere tractive force imparted by the operator through the coupling unit 11 and the respective control rod. During this step, the bare cable conductor 16-due to its friction against the surfaces of the body 1 and of the portion 3B of the camping jaw 3, preferably knurled or indented-is cleared from all oxides, while moving forward, so as to obtain a more thorough contact thereof with the pliers. As it moves forward between the body 1 and the jaw 3, the bare cable conductor 16 presses against the oscillating lever 5 engaging the coupling unit 11, and causes the progressive counterclockwise oscillation of said lever 5 about the pivot 6, thereby lifting its end 17 and simultaneously parting its end 14 from the pin 9 of the coupling unit 11, up to causing the disengagement of the tooth 15 from the pin head 10. At this point, the conductor 16 is housed in its seat (fig. 3), formed between the body 1 and the jaw 3 thanks to the counterclockwise oscillation of said jaw and the clockwise oscillation of the portion 3B thereof. The conductor 16 is thereby stopped from accidental outlets from its seat. At the same time, the spring 7 associated to the extension 5A of the lever 5-which merely acted on the head 10 of the coupling unit 11-becomes inactive, and the lever 5 remains idle on its pivot 6 and no longer imparts any pressure onto the bare cable conductor 16. The coupling unit 11 with its control rod are simultaneously released (as shown in fig. 3), remaining at

the disposal of the operator for any subsequent uses, and the pliers are now in working conditions with the conductor 16 properly retained between the body 1 and the jaw 3.

Once the maintenance operations have been carried out, the conductive conditions on the electric line are restored by removing therefrom the device of the present invention. This is obtained by acting on the ring 12 with a recovery hook (not shown), so as to cause the rotation of the whole pliers up to overturning the same and thereby produce, always by tractive force, the outlet of the conductor 16 from the seat into which it had been inserted, between the body 1 and the jaw 3, thanks to opening of said jaw against the action of the spring 4. Once the conductor 16 has been released, the pliers take up again the configuration illustrated in fig. 1, with the portion 3B of the jaw 3 performing a counterclockwise oscillation upon contact with the body 1 of its end pivoted in 3C to the portion 3A.

It is anyhow understood that the invention is not limited to the aforedescribed and illustrated preferred embodiment thereof, but that several modifications and variants could be introduced therein, all within reach of a technician skilled in the art, without thereby departing from the protection scope of the invention itself.