Quote:
Originally Posted by djlnc
Since you are effectively bringing the ground potential up over the roof with the grounded lightning rods, wouldn't you be making it more likely to attract a lightning strike?
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Although I understand your point, it doesn't work like that.
Lightning is complicated because it can be Cloud to Cloud, Cloud to Ground and Cloud to Structure. Most of the time in the Cloud to Structure case the cloud builds up negative charges and the structure or ground builds up positive charges. When the potential reachs a certain critical point, you get a lightning strike. If you have lightning rods the rods develop a concentration of positive charges at their tips which "draw" the strike to that point if a strike occurs, safely diverting the charge to earth ground vs hitting other parts of the roof causing a fire. There are also other situations that can happen but are too complicated to explain here but this is the basic idea of how the lightning rods work.
So for example, if you have 10 homes in an open field with only one with lightning rods, during a severe storm all 10 homes would build up positive charges on their roofs. If the negative charges in a cloud were strong enough to cause a lightning strike, all 9 of the homes would have a relatively equal chance of being hit randomly on their roof structure causing a fire where the 1 with the lightning rods would most likely be hit at one of it's lightning rods diverting the charge safely to earth ground without damage or fire.