Many people assume that a lightning rod stops a house from being struck by lightning. This is not true. A lightning rod's real job is different: it gives a lightning strike somewhere safe to go, rather than stopping the strike itself. Lightning is simply a very large electrical current. Like any current, it follows whichever path offers the least resistance to reach the ground. A bare rod at the highest point of a roof is connected by a thick metal cable to a grounding electrode buried in the earth. This creates exactly that kind of path: a continuous route with low resistance. This path is far more attractive to electricity than traveling through wood framing, brick, household wiring, or plumbing. When lightning strikes near or on the building, the current follows this path harmlessly into the ground. It does not tear through the building's structure or start a fire. However, a complete lightning protection system needs more than just one rod. Every metal part, such as gutters, vents, and plumbing, must be electrically connected to the grounding system. Any gap in this connection could let a dangerous spark jump across it. Even with a full system in place, buildings often need extra surge protection. This guards against damage carried in through power lines, rather than from a direct strike on the roof.
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