Ask a Teacher

HOW LIGHTNING CONDUCTOR PROTECTS THE BUILDING?

A lightning rod or lightning conductor is a metal rod or metallic object mounted on top of a building, electrically bonded using a wire or electrical conductor to interface with ground or earth through an electrode, engineered to protect the building in the event of lightning strike. If lightning hits the building it will preferentially strike the rod and be conducted to ground through the wire, instead of passing through the building, where it could start a fire or cause electrocution.

A lightning rod is a single component in a lightning protection system. Lightning rods are also called finials, air terminals or strike termination devices. The lighting rod requires a connection to earth to perform its protective function.

The concept of a lightning rod was originally developed by Ben Franklin. Franklin proposed that lightning rods should consist of a pointed metal pole that extends upward above the building that it is intended to protect. Franklin suggested that a lightning rod protects a building by one of two methods. First, the rod serves to prevent a charged cloud from releasing a bolt of lightning. And second, the lightning rod serves to safely divert the lightning to the ground in event that the cloud does discharge its lightning via a bolt. Franklin's theories on the operation of lightning rods have endured for a couple of centuries. And not until the most recent decades have scientific studies provided evidence to confirm the manner in which they operate to protect buildings from lightning damage.

The first of Franklin's two proposed theories is often referred to as the lightning dissipation theory. According to the theory, the use of a lightning rod on a building protects the building by preventing the lightning strike. The idea is based upon the principle that the electric field strength is great around a pointed object. The intense electric fields surrounding a pointed object serve to ionize the surrounding air, thus enhancing its conductive ability. The dissipative theory states that as a storm cloud approaches, there is a conductive pathway established between the statically charged cloud and the lightning rod. According to the theory, static charges gradually migrate along this pathway to the ground, thus reducing the likelihood of a sudden and explosive discharge. Proponents of the lightning dissipation theory argue that the primary role of a lightning rod is to discharge the cloud over a longer length of time, thus preventing the excessive charge buildup that is characteristic of a lightning strike.

The second of Franklin's proposed theories on the operation of the lightning rod is the basis of the lightning diversion theory. The lightning diversion theory states that a lighting rod protects a building by providing a conductive pathway of the charge to the Earth. A lightning rod is typically attached by a thick copper cable to a grounding rod that is buried in the Earth below. The sudden discharge from the cloud would be drawn towards the elevated lightning rod but safely directed to the Earth, thus preventing damage from occurring to the building. The lightning rod and the attached cable and ground pole provide a low resistance pathway from the region above the building to the ground below. By diverting the charge through the lightning protection system, the building is spared of the damage associated with a large quantity of electric charge passing through it.