Lightning Rod

A lightning rod is a metal conductor mounted on the top of a building and connected through a wire to the ground to protect the building from lightning. The rod should conduct the electricity from a lightning strike down through the wire instead of passing through the building. The rod is just a single component in the lightning protections system along with rooftop conductors and multiple conductive paths. Benjamin Franklin invented the lightning rod in 1749.

The taller the building the more dangerous the threat of lightning is. Lightning is capable damaging structures made of most materials due to the large currents involved. In Sri Lanka they installed a tip of copper on the highest point of every building to conduct any lightning charge. This did prevent many Buddhist monuments from being destroyed. In Europe, the church which was the tallest building seemed to be the one most often struck by lightning. Franklin eventually tried his kite experiment since he was tired of waiting on Christ Church in Philadelphia so he could place a lightning rod on top of it.

During the 19th century lightning rods became more of a decorative statement. Many of them were embellished with glass balls which were there to provide evidence of a strike by shattering when hit. William Snow Harris invented a successful system for putting lightning protection on ships in 1820. The British Royal Navy didn’t adopt the system until 1842, after the Russian Navy.

Nikola Tesla patented an improved rod and later in 1919 wrote an article in which he explains the logic of Franklin’s pointed lightning rod. In the 1990’s the lightning points were replaced when the statue on top of the capitol building in Washington, D.C. was restored.

To protect telephone wires a lightning arrester is placed where wires enter a structure. They are also called surge protectors and serve to limit the rise in voltage when a communications or power line is struck by lightning.

Power lines use a lighter conductor wire over the main conductors which is grounded at various points along the link. Electric substations may have a web of grounded wires covering the whole plant.

It is assumed that a lightning rod protected a cone of 45 degrees but it was later found that was not adequate for protecting taller structures. Electricity travels along a path of least resistance therefore locations that are safe from lightning can be determined by imagining a lightning leader’s step potential paths as a sphere that travels from the cloud to the ground. The controversy over rounded tip and sharp tip for lightning rods was finally settled in 2003 after Charles B. Moore found that moderately rounded or blunt-tipped lightning rods act as better strike receptors.

There are also lightning dissipaters which have been widely criticized. They claim to make a structure less attractive to lightning and used for the preventative protection of objects located on the surface of the earth. The dissipaters are supposed to deal with the phenomena such as electrostatic fields, electromagnetic fields, field transients, static charges, and any other related atmospheric electricity phenomena.

The operation of the lightning rod dates back to the 18th century although it is known that the device doesn’t divert but it intercepts the charge and carries it down a structure to the ground. There is also the dissipation theory which states that a lightning strike to a structure can be prevented by altering the electric charge.