One of the most frequently asked questions by people buying weathervanes is “Do weathervanes attract lightning?”, which typically leads to question number two: “How do I ground my new weathervane?”
The answer to the first question is “No, weathervanes do not usually “attract” lightning and actually less than TV antennas do.” If you look around (or remember back a few years), you will see lots of houses with large skeletal TV antennas on them. Typically, these antennas are grounded but not part of a lightning protection system. Grounding is not to conduct a lightning strike to the ground but rather to dissipate the electrostatic buildup in the widespread antenna from the wind, which is especially present during thunderstorms. If the charge is not dissipated, it will actually “attract” a strike and can send it through the building’s electrical system. While no one can say for sure whether lightning will strike a specific area or item, one can estimate the probability of a lightning strike with reasonable accuracy.
As for the second question, “How do I ground my new weathervane?”, the answer is not as straightforward as one might think. The primary reason for grounding a weathervane is for lightning protection purposes. There are two ways to go. One; do nothing and ignore the issue (see the comments on TV antennas above).
The second way to go is to consider the weathervane to be a lightning rod, and incorporate it as part of a lightning protection system. This involves, at minimum, running two heavy cables (which are as thick as your pinky finger) to two ten-foot-long ground rods, on opposite sides of the building along with using clamps, connectors, and other hardware designed for, and approved for lightning protection use.
If you are (or believe you may be) susceptible to lightning, it probably makes sense to have the complete lightning protection system professionally installed, and have your new weathervane incorporated into it.
Now for the strange part. If you choose to do neither of the above but say, decide to ground the weathervane using a smaller gauge wire connected to only one round rod, THIS CAN BE MUCH WORSE THAN DOING NOTHING! “Huh?”, you ask. If you have done the above, you have installed a grounding system that is not adequate for lightning protection. In this case, if a lightning strike does occur, your “halfway” system will most likely not have the capacity to drain off the lightning charge safely. Instead, you will most likely wind up with some damage. It could be severe, such as fire, part or all of your structure destroyed or blown apart, etc, to minor things like blown electrical appliances such as TVs, etc.
Hopefully, you now understand why you need to do one of two things when it comes to grounding your weathervane: A) install a complete lightning protection system or B) do nothing at all. B is the more common method used.
The whole area of lightning protection is a unique field where most electricians and other contractors have very little, if any expertise. Lightning protection is NOT part of the National Electrical Code, which all good electricians know forward and backward.