Disclaimer: I'm not experienced in many phyiscal nor electrical terms and I have no idea where to ask this question elsewhere. I'd be open for a move request if needed.

Today when using public transport in switzerland I noticed something odd. All trians emitted a lot of sparks where they met the electrical supply line. Seen in different train stations on different trains. enter image description here (Image not from today, just as example)
I never noticed even in rain. The only difference from other days was the temperature.

Time / Date: 7:15 - 7:40, January 16th
Sky: Still dark, not cloudy
Temperature: -2°C
Humidity: 92%
Last snow / rain: The day before yesterday

Can these conditions cause an entire train network to emit sparks? If so why? Is there another possible explinations?


The Swiss Federal Railways explained that very same phenomenon in a (German) newspaper article from 2013.

The basic idea is that the cold weather leads to a thin layer of ice forming on the overhead wires. The Swiss rail electrification system works with a voltage $15kV$, which is easily enough to lead to an electric arc between the engine collector and the wires.

On a side note, looking at the arcs directly is not advisable, due to the high light intensity. This effect was (still is) used for movie projectors and high intensity searchlights.

  • 1
    $\begingroup$ As an additional warning, the arcs are likely to contain UV radiation which can damage the eyes. $\endgroup$ – my2cts Jan 16 '19 at 11:39

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