Lightning rods have been around since Benjamin Franklin first discovered lightning was made of electricity, and logic would conclude that if one were to position a metal conductive rod at the highest point on a structure, a lightning bolt would strike it, direct the electricity into the ground, thus averting damage to the structure itself. Unfortunately, it’s not that simple. As strange as this may sound, metal doesn’t attract lightning. Nothing does.
Lightning can strike anything, conductive or non-conductive, and what it does strike isn’t always obvious. For example, the tallest tree isn’t always a guaranteed hit. Neither is a flag pole, a golf club, or a house. Sometimes it’s the ground itself right next to a 100 foot tree.
So what good is a lightning rod, then? If a lightning rod were to be struck, the electricity would pass through the rod, down the metal wire, into a grounding rod driven into the earth. They do work, when they are struck, but how then do we get a lightning bolt to strike a lightning rod that doesn’t attract lightning?
Lightning doesn’t know at 30,000 feet what it’s going to strike on the ground below. As the electric field breaks down between the cloud above and the ground below, the air ionizes in little segments called step leaders. One by one, the step leaders make their way downward, but it’s only in the last 100 feet or so that something strange happens. Objects on the ground shoot “streamers” upwards. When the last step leader of the chain makes contact with the first streamer it comes in contact with, the electric circuit is completed and electricity flows. This is what we see as lightning. There is no way to guarantee which objects on the ground will create a streamer, and even if one is created, there is no way to guarantee it will be “chosen” by the last step leader.
Here are a few facts about lightning rods:
- Lightning rods do not attract lightning
- Lightning rods do not guarantee a lightning strike
- Lightning rods do not discharge the electric field in a cloud
- Lightning rods do direct electric current into the ground
- They do help protect structures when properly installed
The one thing lightning rods do are increase the probability of creating a streamer, which increases the odds that it will make contact with the last step leader. If the streamer is successful in making contact with that last step leader, it will direct the electric current into the ground.
The more lightning rods you have atop a structure, the greater the likelihood that one of them will be struck instead of the structure you’re trying to protect. Modern day lightning prevention systems are composed of multiple pointed lightning spikes that are all connected together with thick conductive cables. In theory, if you have enough rods and cables, you can create what’s called a Faraday cage. The problem with that is, it would be unsightly. So a balance must be attained.