safety of wind instruments on metal pole on roof?

[morr...@gmail.com]

Not strictly weewx related, but:

Any safety concerns with mounting my wind speed and direction instruments on a 1.25" galvanized steel pole, 6 feet above the roof line? 

I currently have a prototype anemometer about 20 feet in the air. It's well away from our house so solar powered, which is proving a challenge.

We get a bit of lightning here, but there are tall trees near our house, and I've never heard of a direct hit in the neighborhood.

Thanks for any experience/anecdotes.

[Karen K]

There are people who lost their electronic equipment in the house including radio, tv set etc. because of a little bit of lightning near their house.

Trees are not exactly lightning rods.

I would strongly suggest to ground the pole using a round steel of about 1/3" (about 10mm). There should be some grounding point in your house, where you can connect that round steel to. You must not use electric wire for that. And I strongly recommend to place that outside your house at the wall.

In case there is no such thing as a grounding point, you need a bar of stainless steel, again about 1/3" (about 10mm) and at least 18 feet in length. The whole thing you drive into the earth. The upper end that looks out of the earth you can connect to instrument pole. As 18 feet are very long, bars of about 3 feet are provided including a thread at the end to connect one to the other. And there are special devices to drive the bar into the earth by vibration.

[Les Niles]

What about using a fiberglass pole instead?  The wires to the instruments could still potentially attract lightning, but probably wouldn’t carry enough current to start a fire — might blow out the weather station electronics, but not burn down the house.  Max-gain Systems sells fiberglass rods and tubes in various lengths and diameters.  

  -Les

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[John Smith]

On Tue, 18 Jan 2022 at 17:11, Les Niles <l...@2pi.org> wrote:

What about using a fiberglass pole instead?  The wires to the instruments could still potentially attract lightning, but probably wouldn’t carry enough current to start a fire — might blow out the weather station electronics, but not burn down the house.  Max-gain Systems sells fiberglass rods and tubes in various lengths and diameters.  

I had a near hit that blew the windspeed/direction port on a davis ISS, so direct hits aren't the only worry. 

[Karen K]

ln77 schrieb am Dienstag, 18. Januar 2022 um 07:11:15 UTC+1:

What about using a fiberglass pole instead?  The wires to the instruments could still potentially attract lightning, but probably wouldn’t carry enough current to start a fire — might blow out the weather station electronics, but not burn down the house.  

I would not agree with that. 

You may be right that the wires are melted fast enough to not carry the current, but lightning does not always need a wire. Air is often enough, and I guess, in this case, too. The house can still be burned down. A lightning hit is a rare event for a certain spot on earth, but if it happens, it is not funny.

[morr...@gmail.com]

Bedrock is only a few feet below the surface here in our area. So the grounding rod isn't really an option. I'll keep the instruments away from the house, I think.

I am reminded of a video I saw years ago, where lightning researchers launched model rockets trailing thin wires into thunderstorms. The thin wires encouraged lightning along their flight path. The video showed a launch, immediately followed by the rocket (and wire) getting vapourized. Here's an example: https://youtu.be/34NpyA2OuaE

[Cameron D]

I decided to use PVC pipe, about 50mm dia. extending 2.5m above the roof line. Lighter to handle and not too flexible.

The cable is easily run down the middle, to the wireless transmitter, which is mounted on a wooden pole.

I don't know if it would make much difference in enticing lightning to strike, but as Karen said once the ionized path is created no vapourization of the wire is going to stop it.  Neighbours of my mother had a bit of electronic kit attached to their back wall with a small wire running upwards - I forget the details. The wire vapourized all right, but not without scattering bits of circuit board and components all over their yard.

Luckily, no fire resulted.  There are plenty of high gum trees nearby, and TV aerials with metal masts protruding from the roof.

[Greg Troxel]

Les Niles <l...@2pi.org> writes:

> What about using a fiberglass pole instead? The wires to the
> instruments could still potentially attract lightning, but probably
> wouldn’t carry enough current to start a fire — might blow out the

This is incorrect thinking about lightning. Lightning is basically a
current source and that results in huge voltages and melted wires.

> weather station electronics, but not burn down the house. Max-gain

> Systems <https://mgs4u.com/> sells fiberglass rods and tubes in
> various lengths and diameters.

If you are in the US, see the National Electrical Code about
requirements for antennas. Yes, I know a weather station is not an
antenna, but a thing on a mast with a wire seems functionally
equivalent.

Memory from last I looked is that the mast has to be grounded, perhaps
to a driven ground rod outside, and that ground has to be bonded to the
service entrance ground. And a lightning protector is required on the
wires entering the house (and the protector also needs to be grounded).

If you aren't in the US, you should consult your local codes of course,
but the physics aren't any different.

Some references:

https://www.arrl.org/grounding-and-bonding-for-the-amateur
http://www.k9yc.com/GroundingAndAudio.pdf
https://www.kf7p.com/KF7P/Tech_Resources.html

[michael.k...@gmx.at]

Regarding the dangers of a lightning strike there is probably not a notable difference which pole material you chose. Also, the probability your house being struck by a direct hit won't be affected significantly with a 2.5m pole on the roof. BUT: If you already have any kind of external lightning strike protection installed, it is essential to connect it in a correct way to this existing protection.

Still, there are no guarantees. I had a Tempest mounted on my roof, on top of a 4m fiberglass/carbon composite mast, and a near strike damaged the humidity sensor last year. The strike was within a distance of 150 - 300m.