Spiral hoar frost and spiral device around telephone or electric landlines

Question

I live in Germany. When I travel by train, sometimes there are cables that run from pole to pole parallel to the train track.

From the lack of insulation between wire and pole, I guess these are telephone landlines, or electrical cables with low voltage.

Sometimes on these black, rubber-covered cables in the summer I see a thick, shiny, metallic or white spiral wound around them for about a metre (3 feet).

It looks something like this sketch:

When it is cold enough for hoar frost to form, the frost on the cables takes on a spiral shape as well. This spiral hoar frost forms not only on the device, but beyond it and along the whole length of the cable.

What is the purpose of those spiral devices on the cables? And why does the hoar frost form spirals?

Answer 1

In the first image, a grounded wire atop a high-voltage tower shows spiral oscillation dampers. This ground cable also contains fiber-optic inside - any curves in the cable must be smooth - the loop in your diagram suggests that fiber-optic is inside the cable that you see from the train.
The second image shows the cable detail where it is routed to a box at ground level. The sheath is spiral-wound. It is likely that frost settles selectively on the spines of the sheath:

Answer 2

Depending on exactly how they are configured, this is probably a spiral vibration damper:

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From what I understand they are useful on smaller cables, to dampen high frequency oscillation from wind, and cheap to install.

I can't answer the part about spiral frost. Maybe the frost forms on the spiral and is then slowly dragged down by a combination of gravity and new frost forming, helped along by the constant tiny vibrations from wind. It would still remain in the shape it had when it formed.