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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)

winny
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SpecialFx
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    yes, in a suburban environment (flat land) a nearby strike can audibly (and simultaneously) produce an audible "tick" as wall-mounted switches and/or power plugs arc over - thunder occurs a few seconds later. A high location could easily provide an electric field environment that extends the range. – glen_geek Aug 06 '18 at 14:49
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    How good is the ground? In dry, rocky locations, it may be difficult to achieve a good ground. See https://www.ecmweb.com/content/achieving-acceptable-ground-poor-soil Also, in the open, there are strong inductive and capacitive effects, causing induced voltages in long conductors. Thanks for posting your interesting anecdotes, BTW. – DrMoishe Pippik Aug 07 '18 at 00:34
  • @glen_geek: thank you! Two questions: - the reason? EMF spike from the power line? - I'm trying to understand if it could be dangerous for us in case of closest lightning strikes, I'm quite worried BTW our location is in the mid mountain, in a mountain pasture surrounded by a wood – SpecialFx Aug 07 '18 at 01:52
  • @DrMoishePippik: thank you too! Our location is not dry neither rocky, rather the high terrain moisture causes humidity problems inside the cabin. Long conductors: yes, it's a suspect I have that the pheriperal location of cabin + lot of cable just to connect us could be a cause; I think I can verify this hypothesis observing if there is a correlation between strike location and the phenomenon intensity: for the last half mile the cable should run quite straight so the EMF should be different if the lightning strikes aside or ahead / behind. I'll give it a try. – SpecialFx Aug 07 '18 at 01:59
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    I've never heard of this effect before, it's quite interesting. If you're certain of the quality of your system grounding, are you certain that each of these metal bodies is grounded? Just to rule out that this could be at least partly capacitive? Just because your house itself is grounded does not mean that each metal object in it was properly bonded together. – K H Aug 07 '18 at 02:39
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    Hard to tell if your interior cabin wiring itself is acting as antenna, or if power line to your cabin is the source. Even with modern 3-wire (hot, neutral, ground) interior wiring, I've heard the "tick" arcs from nearby strikes. No damage done - no fires started. – glen_geek Aug 07 '18 at 02:42
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    A good test for if it's charge built up in unintended capacitors, you can either ground the object manually and see if it stops the sparking (it almost certainly will) and/or use a nonconductive string and hang a piece of wire close to but not touching one of these earthen walls. – K H Aug 07 '18 at 02:43
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    Hmmm... Also tell us roughly how many mm of air you're seeing these sparks arc through. – K H Aug 07 '18 at 02:45
  • @KH: the metal bodies SHOULD be grounded (both water heater and LED lights have the plugs with the ground), I will check it. If not, I agree, ground the objects manually should solve the problem. The hypothesis I think are three: 1) cabin is acting as antenna 2) power line is acting as antenna 3) the terrain around the cabin is acting as antenna (continue) – SpecialFx Aug 07 '18 at 12:09
  • Actually I think that the wiring of the cabin is too small to be affected by lightnings that are 2 miles away; a long straight cable instead should be much more sensitive to EMF; if so I'm expect spikes on both netural and phase, but when devices are powered off just the phase is disconnected, so if there is a spike on the neutral we have a differential potential between it and the wall / ground. Sparks are little, I cannot say exactly but at a rough guess from 5 to 15 mm (1/5" to 3/5"). – SpecialFx Aug 07 '18 at 12:14
  • @glen_geek: thank you, it's reassuring to hear it :) our electrical system is new and uses the 3 wire interior wiring everywhere – SpecialFx Aug 07 '18 at 12:17
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    If the spark is jumping 5mm, that means you have a localized buildup of around 15000V, which leans towards either static electricity, or if it's inductance, it would indicate that the objects were inadequately connected to ground and acting as both antenna and capacitor. I don't think it's likely at all this is coming from your lines, because any resultant voltage there would be from the lines to ground, not from random metal objects to ground. – K H Aug 07 '18 at 21:45
  • @KH: I verified the connection between bodies and ground with a tester and it seems OK; I found a little differential potential between ground and the wall where they are attached, is possibile that this wall could be a better ground than the ground itself (after all the wall has a lot of surface against the terrain, and both have high level of moisture)? However I'll try: 1) to mount surge arrester (both type 1 and type 2) 2) re-check the ground 3) to record, the next thunderstorm, an event with a camera to share it with you – SpecialFx Aug 08 '18 at 07:44
  • I could also try to connect a digital oscilloscope between ground and netural to record any transients, using a resistive divider to avoid to burn the input channel. What do you think about? – SpecialFx Aug 08 '18 at 07:44
  • It would probably help to have a better video. The one you posted doesn't really show anything of use. I also kind of wonder if you could test with a makeshift lightning rod mounted uphill of your house. Ideally lightning rods operate by bleeding static out of the air before it can build enough to create a lightning strike. I'm quite curious and I'll keep thinking about it, but it doesn't seem clear to me without more info. As for the oscilloscope, I wouldn't risk a nice one, but perhaps a cheap one. It'll be difficult to size that voltage divider though. – K H Aug 08 '18 at 23:33
  • @KH: I have added a lot more details + 2 videos to the laptop2d's answer – SpecialFx Aug 17 '18 at 22:59
  • @gleen_geek: just posted 2 videos, duplicate post because I can't notify multiple users with just one post :| – SpecialFx Aug 17 '18 at 23:02

1 Answers1

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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

Voltage Spike
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  • Thank you very much! I think capacitive coupling is the most likely thing, but it's not easy to understand who is responsible. I have some updates that bring some extra elements. Before I heard a spark bursting at the same time as a distant lightning (about 12 km), proof of how the phenomenon is NOT absolutely connected to direct or secondary discharges. Now there was a thunderstorm right here and I noticed that only a few lightning strikes the described effects, it seems to depend more on direction than distance. – SpecialFx Aug 17 '18 at 22:51
  • So far I have only considered two possibilities for capacitive coupling: some elements of the house (e.g. the chimney) the long underground cable that connects us to the electricity grid In reality there is a third possibility: the metal pipe that connects us to the aqueduct. To better visualize the situation I prepared an image: https://snag.gy/5z2NC4.jpg In yellow there is the (presumed) cable route. in blue there is the path of the pipe to the well The red X indicates where the earth post is installed. – SpecialFx Aug 17 '18 at 22:51
  • (the slope increases to the south, the bottom; the level of the land in the south is about 4 meters higher than in the north) – SpecialFx Aug 17 '18 at 22:52
  • BONUS During today's thunderstorm I managed to resume both effects, spark and led: https://www.youtube.com/watch?v=GKW2Awuv63k I verified that the pipe, from the water heater up to where the spark is triggered, is connected to the ground; from there on, no. https://www.youtube.com/watch?v=g5G9EKJeUXo the spotlight has 6 LEDs; the number of LEDs that light up depends on the intensity of the phenomenon; they are NOT reflected. – SpecialFx Aug 17 '18 at 22:56
  • I believe that the capacitive coupling with the aqueduct tube is the most likely hypothesis: on the one hand you have the ground of the house, on the other you have the cold water tube directly connected to the aqueduct tube. What do you say about it? Thank you very much to everyone! – SpecialFx Aug 17 '18 at 22:57
  • Great answer! @SpecialFx If the spark is occurring at the point where things start to be isolated from ground, that explains things, and connecting ground across that gap should alleviate the problem at that location. That spark is much more significant than I would have anticipated. I wonder if a grounding ring around your house with lightning arrestors on it would help or not. – K H Aug 17 '18 at 23:14