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While studying about overhead equipment I came across this video.

The below image taken from the video shows a G-jumper. The electric connection can be made using simple wire without any twist.

Why is this complex shaped wire used to connect these cables?

enter image description here

JRE
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mech_duck
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    A guess: the wire is flexible, not solid. It has extra length because the wires it's attached to are also flexible. And it runs parallel to those wires to allow the use of two connections, perhaps for redundancy – user253751 May 11 '22 at 11:50
  • @user253751 this is in fact the answer. – fraxinus May 11 '22 at 11:54

3 Answers3

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The lower contact wires (only) are pushed up by the pantograph of passing trains so the flexible jumper is shaped to allow the gap between the upper (catenary) and lower wires to reduce as trains pass.

The central loop also allows the two overlapping sets of wires to move independently from side to side.

A free[1] comprehensive guide to UK OHE practice is available at http://ocs4rail.com/

Section 12.4 on page 109 discusses overlaps and their associated jumpers. You should be able to use the search feature of your PDF reader to find other mentions of jumpers in the document.

[1] Charitable donations invited.

Graham Nye
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    In many other areas we use lazy bends so that not-very-flexible cables etc. can accommodate movement. It's common in laboratory gas delivery for example. If you tried to use the minimum length for foreseeable movement, even within-spec flexing would stress the wire at the clamp over time – Chris H May 12 '22 at 08:20
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Double connections avoid torsion stress on the connection points. A single connection would allow the jumper wire to rotate w.r.t. the overhead lines around the connection point in the presence of lateral forces, which would tear the metal apart.

With the double connection point, rotation is no longer possible. Instead, lateral forces would create tension in one point and compression in the other one, and metal parts withstand tension stress much better than shear stress than the rotation would produce.

The extra length of the jumper allows the overhead lines to move independently, so that the presence of the jumper has minimal impact on the longitudinal waves in the lines. Such waves appear as the train's pantograph moves along the line at high speed. A hard join would create a reflection point which would result in (ideally) a double amplitude in certain parts of the wave, which could be enough to wrap the overhead line around the pantograph and thus destroy it.

Dmitry Grigoryev
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Note: I have no knowledge about overhead catenary systems, but the answer seems straightforward:

The connecting wire must be flexible, since the wires it's connecting can move separately in the wind. So, it flexes. And when you connect all 8 points, you get that shape (or a similar one).

I assume that each wire is connected twice for redundancy.

user253751
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