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Thunderstorms Frying My Anemometer Displays

  1. May 7, 2016 #1
    Greetings, folks!

    I an a monk, camped out in an aluminum-framed trailer, high up in the mountains of Utah. I try not to pester you kind folks unless absolutely necessary, but yesterday’s storm has me back to “square one” for this bizarre (at least to me!) behavior.

    Here’s the set-up:

    116' length (most of which is coiled up inside the trailer) of braid-shielded, 22-gauge, twisted-pair cable, going between an anemometer and its display. Specifically, those two items are:

    ● Inspeed Vortex anemometer (reed switch and rotating magnet combo)

    ● Sigma Sport BC1200 display readout (I get mine from the fine folks at Inspeed.com )

    It is an excellent combination (I have two such setups, one at each end of the trailer at different heights) and is dearly cherished; We get serious wind up here!

    The issue is that one of the BC1200s has been getting reset and sometimes fried when severe thunderstorms roll through. This has never happened before in any other location, and I have cherished my Vortex anemometer setups for many years. The two BC1200 displays are mounted next to each other, inside the trailer.

    When a bad storm rolls in, I can hear and see arcs crackling between the two conductors at the end of the braid-shielded cable going to the BC1200, and/or see the BC1200’s screen go blank. This does not happen for every storm.

    Switching from plain, unshielded cable (never a problem in any other location) to braid-shielded cable did seem to solve the problem (I’ve been trying to solve this for a while now), but yesterday’s storm, with no thunder or lightning, again fried yet another BC1200.

    The identical anemometer and display at the opposite end of the trailer has a much shorter (~30") unshielded cable going to its BC1200, and I have never had any problems with it in any electrical storms. The latest frying (i.e. dead; this was the third time this has happened) of the BC1200 certainly seems to be due some kind of electrical field interaction between the trailer frame and the much-longer, braid-shielded, 22-gauge, twisted-pair cable.

    After I disconnect the BC1200 from the braid-shielded cable (often getting a strong jolt doing so!) and put a VOM between the aluminum trailer frame and either of the braid-shielded cable’s quick disconnect connectors, I can get up to 15VDC (sometimes, but rarely, much higher) between the two. The polarity will often reverse! (WOW!)

    I assume that the aluminum trailer frame is creating an electromagnetic field due to the storm, but the braid-shielded, 22-gauge, twisted-pair cable was installed to specifically stop any such electromagnetic interference! It really did seem to work for months . . .

    This is the only location—high up on top of a rocky mountain—I have ever been where this happens! When I touch either end of the braid-shielded cable during such storms, I can get some powerful zaps!

    How can a rainstorm (much less a thunderstorm!) cause braid-shielded, 22-gauge, twisted-pair cable to arc across the two adjacent quick disconnect connectors at either end of the cable, and also conduct voltage to and from the trailer frame? I have even seen this happen when the storm was miles away! There is no short-circuit between the twisted pairs of the cable, or between the cable and the trailer frame.

    I baffled, and this is getting expensive!


    Blessings, and Thank You!!,

    Richard Fairbanks
  2. jcsd
  3. May 8, 2016 #2


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    Sounds like you need to ground the trailer, the cable shield, and the pole the anemometer is mounted on (if it is a metal pole). Eight-foot grounding rods are commercially available at electrical supply stores but some people just use a length of water pipe. Since driving an 8 foot rod into rocky ground is "interesting", you will probably have to use several shorter ones spaced a foot or two apart and then wire them all together. Lightning rods are normally wired with a braided cable about an inch in diameter to carry the high current of a lightning strike. Put the grounding rods where the cable shield can be connected to them before entering the trailer.

    Also run a short, heavy wire from the trailer chassis to the grounding rods. Do not connect this wire to the "skin" of the trailer, the high current of a nearby lightning strike can melt the thin sheet metal at the connection point.

    There are Lightning Arrestors available for TV antennas that are useful for protecting the signal leads. Connect the leads to the two screw terminals and then connect a wire from the Lightning Arrestor to the grounding rods. There should be instructions that come with it. As a final barrier, you could also use Surge Protectors that are available for low voltage signals and for telephone lines.

    Finally, be aware that with lightning there are no guarantees, there is just too much energy involved.
  4. May 8, 2016 #3

    jim hardy

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    Sounds to me like "St Elmo's Fire"

    Is it the higher one giving the trouble ?
    first part of this talks about electric field accompanying thunderstorms

    Is your shield not earthed ? Is either of the wires from the reed switch earthed ?
    Is the trailer frame earthed by incoming utility power ?

    I would connect anemometer shield to metal pole outside and earth the pole. That gives a drain and will encourage lightning to follow the pole down to earth outside your living quarters.
  5. May 8, 2016 #4


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    Some locations are much more lightning prone than others. It sounds like you may be in one of those hot spots. You should worry about your personal safety more than your gadgets.

    Take heed to what others in this thread told you about grounding. In addition, if you have metal pipes in your plumbing, double check the earthing of that.

    Above all, avoid stepping outdoors during one of those storms. If your mountain top cabin has an outhouse, you should keep your legs crossed and not visit it during a storm.

    Make sure your life insurance is paid up, that your will is up to date, and that someone not on the mountain top will check up on you following each storm. You may be living in a very hazardous spot.
  6. May 8, 2016 #5


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    Raindrops prefer to form on nuclei of dust or pollution that carry a charge. Those small drops merge in the cloud to form larger drops that fall faster, so some drops of rain carry a concentrated charge that may be dumped onto your equipment and cables as the first rain drops fall. That charge flows over wet insulation surfaces and so reaches the conductors.

    In my experience with long wire antennas it is usually only the first rain in the shower that carries most of the charge. That is because earlier drops falling to the bottom of the cloud evaporate and so concentrate charge at the base of the cloud. When the rain first reaches you and the mountain, it is effectively the charge in the base of the cloud that you are encountering.

    You can listen to charged rain by tuning an AM radio between stations. Lightning strikes sound like random clicks, then crashes. But charged rain sounds like a tick as each drop falls on the “antenna”. That can increase exponentially to become a rising scream before it suddenly stops, when the bulk of the steady rain begins to fall.

    It is better to short circuit cables and Earth them than to disconnect them, disconnected conductors lead to high voltage sparking and insulation breakdown. Maybe you should consider moving to a lower profile location, or installing some independent lightning conductors nearby.
  7. May 11, 2016 #6


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    I think you should move to a less dangerous location.

    Google found..

  8. May 15, 2016 #7
    First, thank you, Tom G. for your advice! I was assuming grounding the trailer frame would probably be necessary; your detailed advice was much appreciated! Alas, it did no good . . .

    To everyone else who offered their much-appreciated advice, please forgive me for not responding much earlier to your posts; I had not gotten any email alerts since Tom G.’s initial response and did not know that there were any other responses. I have gone through your posts, and I THANK YOU for your many suggestions! Please allow me to quickly respond to a few:

    A delight to hear from you, Jim! I really appreciated your kindness in my thread from last year, and, yes, “St. Elmo’s Fire” would not surprise me! ;-)

    Yes, it is the higher anemometer; the cable runs right alongside my point-to-point wireless antenna cable, which couldn’t care less about any storms.

    Thank you, Baluncore! I have long noticed that the most damaging voltage surges seem to occur shortly after the rain starts to fall. I just don’t want to have to start removing the BC1200 from its mount every time it starts to rain. This was never necessary before!

    The cable’s braided shield is grounded, but neither of the conductors. I am curious as to whether grounding one of the conductors would impair the signal, given that the circuit is running off a small CR2032 battery. Thoughts?

    I am not sure I understand what you mean, Baluncore, by “short circuit cables and Earth them.” I much-appreciate your advice on not disconnecting cables; sometimes it is necessary . . . like removing a BC1200 from its mount before I hear an arc and see its screen goes blank.

    Thank you, CWatters, for the link, it was quite helpful!

    Please allow me to offer some more details:

    - First, I am currently not able to move my hand-made, aluminum/polycarbonate, camping trailer to another location. If the Gang Upstairs wanted to kill me, they had their chance.

    - FYI, no other electrical devices in the trailer have ever had any such problems, and there are many, from hand-made LED lighting arrays to a desktop computer, some running on long lengths of plain zip cord, and even running alongside the circuit that is frying my anemometer displays. (I also wonder if grounding the trailer frame will increase the possibility of a direct lightning strike, now that it is no longer insulated from the Earth . . . )

    - Yesterday, based on Tom G.’s suggestions, I drove four lengths of copper-plated grounding rod into the ground, each spaced about a foot apart from the next in line,, and grounded both the trailer frame and the braided shield for the cable. I was only able to get the four rods about a foot each into the ground before hitting rock; I had tried many times in various places to get deeper, this was the best I could do.

    - Today, the brand-new BC1200 (replacing the one fried a week ago) was also fried, within a few hours of mounting it, as a rainstorm rolled in. Only a common rainstorm, with the usual winds preceding it, was involved both times: a week ago, and today. Using braid-shielded cable seemed to solve the challenge that was force-resetting, but rarely frying, my BC1200s during thunderstorms last summer, and those storms were much more severe than those currently frying my BC1200s. Please understand that this sudden frying of anemometer displays has never happened under these conditions before, going back many years, and has now happened twice in one week when there was no (apparent) thunderstorm involved. (I do have experience watching BC1200s getting reset when the thunderstorm was both directly overhead and several miles away., but never so completely fried.)

    I have looked at lightning arrestors and surge protectors on Digi-Key (they seem to be generally lumped together), and simply do not trust my lack of knowledge in this regard to make an informed choice. Thus, I humbly ask that one (or more!) of you advise me not only on what lightning arrestors and/or surge protectors I need to purchase and/or what I now need to do to stop throwing out fried, BC1200s, but also,

    Why is this happening, and to just one circuit?! How is the electric energy, from a (presumed) ordinary rainstorm, creating such powerful voltages in a cable designed to address such conditions, with no discernible impact on any other unshielded circuits?

    I have never needed to use braid-shielded, twisted-pair cable before, much less grounded, and with only a mild rainstorm, how can the ends of the two conductors inside such a cable be arcing between their connectors and suddenly create 18+V to and from the trailer frame?!

    Only the one circuit going to a wooden-pole-mounted anemometer is repeatedly being damaged, and it is suddenly getting much worse. Even the reed switch in the anemometer was unscathed today! Previously, the reed switch would always get frozen (welded?) closed during any thunderstorm capable of frying a BC1200!

    Please forgive my PTSD-fueled plea; I an trying to rebuild my life after a horrific accident and need to understand why this is possible, besides just solving it!


    Blessings to you all!,

    Richard Fairbanks
  9. May 15, 2016 #8
    Greetings, folks!

    After long-pondering Jim’s and Baluncore’s questions about grounding one of the circuit’s conductors, I noted the following:

    - Being completely off-grid (many miles from asphalt), all electrical devices in the trailer are running, directly or via the DC -> AC inverter, off the 12V battery bank.
    - The negative lead from the battery bank is grounded to the trailer’s frame.
    - Therefore, every electrical device is grounded to the trailer frame . . . except for the anemometer; it has its own power supply (a 3V CR2032 “coin” battery). But it’s still a DC, battery-based power source.
    - The aluminum frame is large enough such that the inverter actually thinks of it as a separate ground.
    - Therefore, one possible reason that I have not had any problems with any other electrical circuits in Sam, is that they are all grounded to the trailer’s frame.
    - Thus, in theory, I should be able to use just a single conductor from the positive side of the BC1200 going to the anemometer, and ground the negative leads from the BC1200 and the anemometer directly to the trailer’s aluminum frame, at opposite ends of the trailer.
    - I could then also (to minimize the circuit’s resistance) just tap off the negative lead of the BC1200 and run a separate “ground” to the trailer frame . . . just as Jim and Baluncore were implying.

    There should then certainly be no voltage building up between the negative lead and the frame! Given the reed switch closing every second or less, any voltage build-up in the positive side of the line should be mitigated . . .

    I will test this out tomorrow; I’m going to bed! (I just wanted to post this before any of you read my previous post, to try and spare you some needless, but always-appreciated, efforts!)

    There are still unanswered questions as to why this is happening at all, but I believe a solution may be possible. Time to order yet another BC1200 . . .

    Just FYI . . . last summer, on a calm, sunny afternoon, after yet another reed switch fried closed due to a thunderstorm about seven miles away, I was standing on a plastic bucket, wearing rubber-soled sandals, and got blasted by a big jolt when I touched the wooden pole to which the anemometer was mounted.


    (I do wonder sometimes about just what might be under the ground upon which my trailer is sitting . . . )

    I’ll let you know how the next few days of storms go!

    Blessings, and THANK YOU!,

    Richard Fairbanks
  10. May 15, 2016 #9

    jim hardy

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    ? Wood pole, eh ? And the one on metal pole doesn't fry, per post 7 ?
    Real quick refresher here.
    Recall that voltage is potential difference , that is why voltmeters have two test prods . The meter reports the difference between the potentials of the two points where you hook its test prods.
    If you hook both of them to the bottom of a lightning bolt
    the meter will correctly report zero volts
    because both see a behemoth potential
    and behemoth minus behemoth is a difference of zero.

    In my power plant.... lightning protection system consisted of a "Ground mat" , a mesh of thumb sized wires buried twenty feet down to which the lightning rods were directly connected also by thumb sized wires. The mesh had grounding rods driven down another twenty feet or so into the salt marsh. Plant's power ground system was not so deeply buried.
    The idea was to make an equipotential "Carpet" atop which the whole plant "floated", electrically speaking. If a lightning strike briefly raises the potential of the whole plant , the instruments see no potential difference so are unperturbed. The generously sized lightning wires were sufficient to pass most lightning bolts without creating much voltage . Only once did i see lightning trip the plant and that was a huge bolt that struck top of containment building while some lightning protection system wires were disconnected because of construction in the area. (Luckily nobody was working up there at the moment) .

    Point being
    you want your St Elmo's Fire to flow from the earth to the sky either through metal structures or through wires that you put there for that purpose. Not through your instruments.
    I hope your camper is an aluminum skinned one, that puts you inside a Faraday shield of sorts.
    Presumably it is tied to earth by the incoming power feed ? Do you have an electric company feed and meter? If not, dust some salt or washing soda around your attempted ground rods to improve soil conductivity. Granite is an awful place to try and ground.

    Next, give your Elmo's Fire a path from ground to the top of the wood pole that does not go through your anemometer like the anemometer signal wires do. The wood pole itself is a poor path. I would run a heavy wire from top of pole into the earth , and tie it to trailer frame below the living quarters . Tie-wrap it to the pole every foot or two. At the top bend it out away from the anemometer cups and route it higher than the anemometer by a foot or two. St Elmo likes to exit from a sharp point and the end of the wire gives him one. A lightning bolt will follow Elmo into that wire and hopefully not into your anemometer.
    The wire you'll add to the pole suppresses the kilovolts per foot E-field that the lightning is following so hopefully it won't get through the anemometer housing. Are the cups metal ? Is the metal shaft insulated form the signal wires ? limiting the local potential difference should save the anemometer .

    Last thing
    when lightning strikes your camper there will be kiloamps flowing through it. They flow into the earth and spread out from there.
    So there is a potential gradient radiating out from the point of entry to earth.
    I believe that's why tropical wading birds sleep standing on one leg.
    You get the idea - take short steps or stay indoors during lightning storms. Don't stand on the ground with one hand leaning on the trailer.
    St Elmo Fire is low current so it doesn't generate much voltage along a metal wire
    but plenty along a resistive wood pole

    so St Elmo goes right up those signal wires from inside your trailer, out through the anemometer into the air
    Protect your anemometer against St Elmo by making the wood pole conductive as i described above. Give St Elmo a path that's not through the anemometer but around it. A ground wire going up alongside the pole.

    Be aware,
    when lightning is around,
    most strokes are just tens or hundreds of amps. 30 kiloamps is an unusual whopper and they can get into hundreds of kiloamps. So you want the lightning bolt to establish itself a path through something that a whopper can vaporize , hopefully keeping the fireball outside your living quarters, and establish an arc out there. Once it's established the arc probably won't grow much .
    Stay away from wires that lead outside and up.

    Did i convey the concept of potential ? And of equipotential ?

    Do you call the wind Mariah ?

    old jim
    Last edited: May 15, 2016
  11. May 15, 2016 #10


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    There was a short newsclip on TV of a car that had taken a direct lightning hit. The hole in the roof you could put your fist in, and there was damage on a wheel rim where the bolt had leap to ground. I'm not certain now whether the vehicle's tyre had burst, but I expect that was the case. The driver was uninjured, though quite shaken.

    I think a lightning arrestor for your semipermanently parked van would be a wise precaution. ⚡⚡⚡
  12. May 15, 2016 #11
    One idea would be to stick a metal pole in the ground some distance away, but not too far from stuff that you don't want to get damaged.
    If that metal pole is higher than the stuff you want to protect, a lightning stroke will be more likely to attract to that as the easiest route to discharge.
    An Iron, Copper, or Aluminium pole is probably affordable, but a pole made of Gold might work better.
    Last edited: May 15, 2016
  13. May 16, 2016 #12


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    ref: post #9
    ref: post #11
    Both are very good ideas. The rule-of-thumb for lightinig rods is they protect in a cone from their top down to the Earth at either a 30 or 45 degree half-angle, depending on which source you choose to believe. (BTW driving a nice, soft Gold rod into a mountain could be 'entertaining / frustrating'!)
  14. May 16, 2016 #13


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    commercial earth rods are usually galvanised iron
    used 100's of then when I worked for Telecom NZ

  15. May 16, 2016 #14


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    Your problem is almost certainly not always lightning strikes. A nearby lightning conductor will not resolve the problem.
    Think of a flowing river. You reach out with a net and hold it in the water to catch whatever is in the river. You must empty the net regularly. If you do not, then you and the net will be damaged due to the increasing accumulation.

    The presence of nuclei such as dust, pollen and pollution enhance charge concentration in the region of the cloud base. The wind is like an invisible “river of charge” that flows over the mountain. You raise an anemometer on a wooden pole which then collects charge from nuclei in the wind as it flows by. Your anemometer circuit is not well connected to earth, the voltage increases as charge is accumulated on the capacitance of the circuit to earth. At some point the air insulation breaks down resulting in the spark between cable conductors.

    You need a path from the anemometer and it's circuitry to common ground.
    1. Replace the wooden pole with a metal pole or run a wire from the top of the pole to ground.
    2. Clad the anemometer housing in a metal sheet or mesh that can be connected to ground through the pole or wire.
    3. Connect a neon globe from each anemometer wire to ground. That will keep the voltage below about 100V and so prevent arcs jumping between conductors. https://en.wikipedia.org/wiki/Neon_lamp
    4. If necessary static build-up on plastic surfaces can be reduced by wetting the surface with diluted ethylene glycol antifreeze. Ethylene glycol is hygroscopic so the surface stays damp and provides a path for surface currents to reach the grounding electrodes.

    Lightning strikes are a separate problem.
  16. May 23, 2016 #15
    Greetings, folks!

    Thank you all for your advice and flood of information!

    As Baluncore noted above (thank you, Baluncore!), this thread really isn’t about lightning strikes, it’s about why my BC1200s were getting fried by the electric fields of passing storms, and how to better protect them. Many of you have greatly helped me understand the nature of electric fields in passing storms, even those not producing lightning. Thank You!!

    After three days last week of thunderstorms, and more days of high winds <shudder> , I believe that grounding the negative lead from the BC1200 to the trailer frame may be all that is necessary, given no immediately adjacent or direct lightning strikes. (Just FYI, the trailer frame is essentially a rectangular aluminum box with each of the six sides of that box containing parallel beams of square and rectangular aluminum tubing to frame the sheets of clear polycarbonate walls and the skylight. There is about 1,100 pounds of 6061-T6 aluminum tubing in that frame, thus it may offer some slight degree of “Faraday Cage” qualities.)

    What still has me curious is how, given the braided shield around the (117', mostly coiled) cable coming from the wooden-pole-mounted anemometer, can charge accumulating (I assume!) _somewhere_ (the aluminum trailer frame, the wooden pole, the braided shield itself, or . . . ) get transfered to the conductors within that shielded cable? The short pair of leads emerging from each end (anemometer and BC1200) of the braid-shielded cable are no longer than the identical leads between the lower, matching set of anemometer and BC1200, mounted almost adjacent to each other, at the opposite end of the trailer from the pole-mounted anemometer. The only difference between the two sets of anemometers and BC1200s is the braid-shielded cable going to the top of the wooden pole, and there has never been any problem with the lower set of anemometer and BC1200.

    Thus, one question remains: How is the storm’s charge getting transferred to the conductors within the braid-shielded cable?

    Some possibilities:

    - If the exposed leads are identical, is the height of the pole-mounted anemometer all that is necessary for the accumulated charge (in the wooden pole or just within the leading edge of the storm?) to flow into the short, exposed anemometer leads at the top of the pole?
    - Or is the braided shield around the cable insufficient to stop increasingly stronger accumulations or concentrations of charge in the wooden pole, the trailer frame, or just within the leading edge of the storm?
    - Or is it just the long length of the braid-shielded cable causing it to attract said accumulated charge?

    Given that no BC1200 has died in the last week (and again, this hasn’t happened before two weeks ago, with identical conditions), I currently expect that grounding the negative lead from the BC1200 to the trailer frame was adequate to solve the current problem.

    It was the kind advice and teachings from those who took the time and effort to respond to this thread that made me make a simple change that seems to be all that was necessary.


    Blessings to you all!,

    Richard Fairbanks
  17. May 23, 2016 #16
  18. May 23, 2016 #17


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    Here are a couple references that provide some necessary considerations when grounding for lightning.

    Last edited by a moderator: May 7, 2017
  19. May 23, 2016 #18


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    Maybe it is collected on the damp surface of the anemometer and crosses from there to the reed switch terminals. You could test that by insulating the reed switch and terminals in one heat shrink tube with hot melt glue.
    A single bare wire connected to the braid might be wound around the sealed switch to mop up any leakage charge.

    Electrostatic Induction, AKA "Electrostatic Influence", is quite different to Electromagnetic induction.
    See instead; https://en.wikipedia.org/wiki/Electrostatic_induction
    Last edited: May 23, 2016
  20. May 23, 2016 #19
    Last edited: May 23, 2016
  21. May 23, 2016 #20
    Carrying on from my earlier post, you could make a ring of 6 or maybe more metal poles in the ground surrounding the protected central area.
    Just cheap iron scrap poles should work, sort of a Faraday cage, but not the whole shebang.
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