How Does a Lightning Rod Protect a House?

Step 1 of 5

Lightning takes the easiest path it can find.

Charge builds until air breaks down along the shortest, most conductive route. Tall and metal beats short and wooden, every time.

Step 2 of 5

Sharp points concentrate the charge.

Electric charge crowds onto sharp tips, so the air just above a pointed rod breaks down first. The strike is aimed there before it reaches anything else.

Step 3 of 5

The cable is the important part.

A thick copper strap runs from the rod down the outside of the building to a plate buried in damp soil, giving the current a wide unbroken road.

Step 4 of 5

Without one, the current improvises.

It jumps through wiring, pipes and damp walls instead, and water inside a wall flashes to steam so fast that the wall explodes.

Step 5 of 5

Which is why it needs checking, not just fitting.

A corroded joint or a broken strap turns the whole system into a metal aerial with nowhere to send what it catches.

Franklin proposed the rod in 1752, and it is one of the earliest pieces of physics that immediately saved lives.