Electronic – Sparks on grounded metal bodies on lighting strikes in the nearby (two miles)

electricityelectromagnetismemflightningspark

I have a strange phenomenon in our mountain cabin, on the Italian alps: lightning strike on the nearby (not so near: < 2 miles) causes audible / visible sparks on:

  • electric / fire wood water heater pipes (very frequently)
  • LED spotlights (rarely)

Both have the bodies grounded.

Details:

  1. In the dark I also see LEDs lighting up (just a weak flash)
  2. The nearest lighting I saw was > 1/2 miles from cabin so I cannot say how the phenomenon is affected by distance from strikes
  3. Electric system and ground are new and tested. I already asked to our electrician but he says that our ground is good, and he don't know what can cause the phenomenon (this is why I write here 🙂
  4. It seems that sparks occours only with metal bodies physically attached to a wall that has the ground on the other side (the cabin is on a slope; the ground level on the back is about 4 meters higher than on the front. Wall is made of stones and concrete, about 30" width)
  5. The cabin is one of the last one of the electric branch on which we are connected
  6. Water heater has a metal exhaust pipe (about 10 feets long) that run inside the masonry flue

For my knowledge strikes are too far to have a direct role, so I tend to thinking about spikes on the power line (the last mile is underground);
but a spark means a LOT of potential difference – and not destructive ones + no failure on the electronic devices I have plugged in 365 days/year means very little current, so I tend to exclude the power line.

Yes, I'm confused 🙂

Thank you very much

Ps: I found a video

https://www.youtube.com/watch?v=DuNLm284m80

You can hear the sound of / see (indirectly) the flash of the spark, but in this case the lightning is in the nearby, I can expect that could induce a lot of EMF; in my case lightnings are a lot far away (also > 10 seconds between lightning and thunder)

Best Answer

Short answer, lightning carries so much energy in the form of electromagnetic waves, it can create current in objects a few km's away.

Lightning can create electric fields that are more than 100kV/m directly, shown from data taken from a plane-strike.

enter image description here Source: http://www.atmo.arizona.edu/students/courselinks/spring15/atmo589/lecture_notes/apr03_2015.html

These taper off with near field and far field rules. If the lightning were obeying far field rules the electric field would taper off with the distance squared. These fields can still can be quite high even only 1km ( or a few kms) away from the strike, a 1m conductor would experience capacitive coupling of a few hundred volts a few kilometers from the strike.

I expect that the stove pipe is a little longer than this.

Here is the fields from a simulated strike. Even the magnetic fields are in the A/m range. Every conductor every wire could also have current inductively coupled into it.

enter image description here Source: Analysis of lightning electromagnetic field propagation in mountainous terrain and its effects on ToA‐based lightning location systemsenter link description here

At even a trace of 1cm could experience a few volts across it, which may be why your LED's are lighting up.

Apparently nearby mountains amplify electric fields as shown in this simulation (although the wave and the mountain in the simulation are not on the same scale, perhaps this is leading to even more amplification of the EM-waves):

enter image description here Source: Analysis of lightning electromagnetic field propagation in mountainous terrain and its effects on ToA‐based lightning location systemsenter link description here