My Wife's idea.

My wife came up with the desire to have a weathervane on top of our Barn.
It seems like an ok idea, especially since it can be clearly seen.
My concern is that it will be mounted on shingled roof and I think it should be grounded.
If that is true and necessary, what size copper cable should I use.
Like I told her, grounding will probably cost more then her chosen $149.00 weathervane????

They make a woven aluminum lightning rod grounding wire. Probably lots cheaper than copper.

It will attract lightning if you ground it, will not make a difference if you don't. I would leave it alone.

My non-expert answer - don't ground it.

Adding a weather vane does NOTHING to increase your barn's chance of getting hit by lightning.

Grounding the weathervane might give lightning a less destructive path to follow IF your barn ever got hit, right at the spot the weathervane sits - but if you're not worried about it now - adding a weather vane shouldn't change anything.

It's a common misconception that metal will attract lightning. It does not.

Just take an old hemp rope and paint it silver, all the grounding you need. Ellis

If you had a system already you could add a weathervane into it. Meaning you already have lightning protection and put a new lead up to the wvane. . If not it is probably best to not ground it at all as it will no more attract lightning than a tv antenna.Normally it is not a woorry about grounding one at all.Lightning protection is a whole separate dept of electrical work and the license might by federal not state. I think you just have to pay money not take a test . But anyway I'm going with no grounding.You can also research number of lightning strikes in your area as they are recorded.

I have never seen one grounded.

(quoted from post at 23:48:56 12/02/13) I have never seen one grounded.

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I have a friend that has one that is grounded. It was with the home when he bought it and it is on top of his home.
I will have to go with NO GROUND and save the expense and labor.

While I had some experience in lightning protection engineering yearssssssssssss ago, I've slept since, so I will just offer a few thoughts bearing no more expertise and credibility then Billy Bob or Bubba's opinions:

If I was going to invest in a full blown proper engineered and installed lightning protection system, sure Id take a look at those weather vanes. However, absent a proper system I don't see all that much advantage in earth grounding a single weathervane and probably wouldn't mess with it as you could do more harm then good if its not done correct and as an entire system. Absent the proper cone of protection with large enough braided copper cables and electrodes, simply sticking up a weathervane with inadequate coverage and inadequate earth grounding and cables could attract lightning which might jump to the building and burn it down.

Again, NO warranty its been too long, but if I were sticking up a weathervane on my barn Id probably not mess with grounding unless I did an entire proper system. In the event you choose to do otherwise, large braided copper cables and an entire system of GroundING Electrodes is gonna cost more then the weathervane Id guess.

Your money your choice.

John T

I have a weather vane on the barn , and it's never been grounded. Lightning hit the yard light pole once, and the tree once.

Donno about lightning not attracted to TV antennas, but have been hit several times on HAM RADIO antennas. Usually a fiberglass sheathed antenna comes down looking like a feather duster. Have taken down fiberglass antennas with copper caps that looked like some kid was practicing arc welding on it. Now, given, they were "slightly" higher than a typical TV antenna. But the hardest hit I ever witnessed on a ham radio antenna was only 40 feet high, and surrounded by trees.