Weather Vane Placement

[PeteC]

For any electrical and/or lightening experts out there. I have a 30" aluminum wind directional weather vane. There are two spots where it could be mounted:

1) On top of the pool pump house which is constructed with four steel rebar reinforced corner posts sunk down 1 meter into their foundations. House is filled up with electronic gear such as house water pumps, pool pumps, chlorinators etc., which are all on their own circuit breakers.

2) On top of our sala which has four teak posts sunk 1 meter deep into concrete foundations.

When mounted on either, the vane will be about 4 meters lower than the peak of the surrounding houses (3), all of which are about 20-30 meters away.

Which would you choose, and do you think the grounding for both as explained above is adequate, or should there be a separate "lightening rod" type grounding wire attached directly to the vane? Thanks. Pete

[Nereus]

Probably better to place it somewhere around Hua Hin, where we do not get such nasty storms!
Does the weather vane have an electrical feed to a display inside the house?

[Terry]

............. a separate "lightening rod" type grounding wire attached directly to the vane? Thanks. Pete

Most definitely Pete

Simply because if the vane IS in a location to attract a strike, the last thing you want is to 'ground' it through any existing set up.

As you know, Thailand can get some severe storms, some of which can do extensive damage from the lightning.

Spend the extra few baht and get peace of mind.

[PeteC]

Thanks Terry. No Nereus, just sits there looking pretty with a horse/carriage on top and spins in the wind. Pete

[Nereus]

Which would you choose, and do you think the grounding for both as explained above is adequate, or should there be a separate "lightening rod" type grounding wire attached directly to the vane? Thanks. Pete

Lightning will follow the path of least resistance, in the electrical sense. The path of least resistance includes, but is not limited to, the effectiveness of the actual "connection" with the earth. you may have what appears to be a "good" lightening conductor, but if it is not properly "earthed" the lightening may very well travel else where to ground.

In lightening prone areas you should have a dedicated conductor that is higher than any other likely conductor, earthed or grounded via a "mat", or some low resistance material, constructed from some non-corroding material such as copper. Ideally it should also be placed in a position that remains moist, but this is not really a problem in the tropics.

Lightening current flow can rise to several hundred thousand amps, so a piece of left over house wiring will not suffice. As there is not really any practical way of knowing which part of a structure or building is going to offer the path of least resistance, I would not be relying on any "earthed" part of anything to be effective. As Terry as stated, a dedicated, separate lightening conductor should be used. Getting such a thing off the shelf in Thailand is unlikely, so you maybe obliged to try and make one up from what is available.

[PeteC]

The wife tells me they have special coated wire here named "sai din" especially for the purpose of grounding things. I was thinking of fastening one copper end to where the vane is mounted, bring it down the side of the structure and into the ground. The ground spot I have in mind is concrete so we'll have to drill, insert another rod of some kind, then wrap it with the other end of the copper wire. Sound reasonable? Any idea how deep the in ground rod portion should be? Pete

[Frank Hovis]

You can get 2 and 3 metre copper ground spikes in most bigger hardware shops. Once through the concrete and depending on your soil you can drive them in with a hammer drill set to hammer only and a tile hole cutter bit over the end of the rod. Clamp the wire to the rod a few times to ensure a good contact.

[Terry]

Frank is correct

You can buy the rods in one meter lengths and they screw together so you can have 1, 2 or 3 m lengths.(You would be hard put to make them go any deeper). 2m is normally ok.

Also - try to avoid bending the connecting cable through too sharp an angle - anything more than about 45 deg should be avoided.

[Nereus]

The wife tells me they have special coated wire here named "sai din" especially for the purpose of grounding things. I was thinking of fastening one copper end to where the vane is mounted, bring it down the side of the structure and into the ground. The ground spot I have in mind is concrete so we'll have to drill, insert another rod of some kind, then wrap it with the other end of the copper wire. Sound reasonable? Any idea how deep the in ground rod portion should be? Pete

Well, I guess that is the Thai answer! The coating will serve no purpose, it depends on what it is coating! The cross sectional area of the conductor is the important bit, plus what material it is.

The ground spike as suggested is the minimum, but they are NOT designed to carry the amps likely to be found with a lightning strike. Several of them grouped together would be better.

If you do it like you suggest and you do get a strike it will probably completely destroy your horse and carriage!

[PeteC]

.....If you do it like you suggest and you do get a strike it will probably completely destroy your horse and carriage!

Turn it into a hybrid no doubt. Pete

[PeteC]

I had another thought Nereus about offshore oil/gas rigs. I think you have experience with those. They must be struck by lightening all the time. Some are not even anchored in the sea bed but float with only the drill shaft touching ground. How in the world do they set up a lightening rod on something like that? Pete

[Frank Hovis]

Sorry I misread your OP - I thought it said 30' (30 feet) not 30" (30 inches).
I doubt very much that it will increase the chances of a lightning strike anymore that the buildings you intend to mount it on and really don't think there is any need to earth it at all. As mentioned lightning rods on buildings are there to provide a path of low resistance to avoid damage to the buildings, not to 'attract' lightning. If you were happy with the odds that your sala would be scorched by lightning before you add the weather vane, I think the odds will be much the same after.

[Nereus]

I had another thought Nereus about offshore oil/gas rigs. I think you have experience with those. They must be struck by lightening all the time. Some are not even anchored in the sea bed but float with only the drill shaft touching ground. How in the world do they set up a lightening rod on something like that? Pete

Yes, I had it happen once on a Drillship. We were not operating at the time and I just happened to be in the drillers control shack when it hit. Every light and alarm horn in there started flashing and sounding off! Surprisingly, nothing was damaged, and this particular unit had a lot of both electronic, and analogue systems.
Other than that I have never seen it happen. Jack Up type rigs are firmly fixed to the seabed whilst operating, as opposed to a floater, but I guess in the first instance there is a good ground, and with a floater a big area in contact with the sea.

To do damage the current discharge has to actually flow "through" something, and going back to my original comment, it WILL find the path of least resistance. Other material may be in contact with whatever is struck, but unless the flow is actually through whatever it is, then it will most likely not be damaged. A lot of damage can be caused by the arcing of the current flow as it jumps around doing its thing, and that can even occur with best of deliberate conductors.

[PeteC]

Maybe I'll forget the whole thing. Pete

"Wat Arun demon loses head to lightning, sparks talk of ill omen".....

http://www.nationmultimedia.com/nationa ... 92712.html

[chaspul]

prcscct

I have had a 3m steel rod on the top of my pool house for the last 3 1/2 years to mount my weather station. Thought at the time about a ground earth and decided that the unit and pole would be fried before entering the concrete of the pool house and not worth saving. All connections to the house are by radio. Have not had a strike during this time. Have a spare, new 3m rod if you are interested.

Chas