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Source: www.noaa.gov

Lightning is one of the most intense natural forces, harnessing tremendous amounts of energy that is capable of destroying buildings and unprotected equipment in seconds. With over 22 million strikes each year, lightning is responsible for more than $5 billion in damages across the U.S., according to the National Lightning Safety Institute (NLSI). A Carnegie-Mellon study also showed that one third of U.S. businesses are affected by lightning; in fact more are affected by lightning than by floods, fires, explosions, hurricanes, earthquakes, and violence.

There are several different types of surge protectors for lightning. Historically, lightning rods were designed to protect buildings and other structures by establishing a low-resistance path to ground. If a strike takes place, the rod conducts the harmful electrical current away from the structure and safely to the ground.

Lightning arresters are installed on transmission and distribution lines to protect electrical lines and equipment. The idea for the modern day lightning arrester evolved from the lightning rod, but takes advantage of a unique material characteristic to provide additional equipment protection. During an excessive voltage surge, the characteristics of the lightning arrester change, sending the excess energy through the arrester and to the ground, not through the piece of equipment or circuit that it is designed to protect.

Lightning arresters do not have the capability to protect every point on the network, however. This is why customers in areas that are prone to lightning strikes add another layer of protection by installing another surge protection system. Even with another system, 100% percent protection is probably impossible, as well as cost-prohibitive. 

How It Works

The lightning arrester uses a gas-filled gap that acts as an open circuit to low potentials, but becomes ionized and conducts at very high potentials. If lightning hits an electrical line that is protected by an arrester, the gas-filled gap conducts the current safely to the ground.

Lightning arresters are a relatively inexpensive solution used on all types of buildings, particularly in regions of the country with a great deal of lightning activity. When used alone, lightning arrestors typically provide line protection for power surges within a customer's facility or from the power company, but may not be capable of handling a direct hit. They can be used, however, in combination with other surge protection devices to handle a broad range of electrical surges.

Modern building protection systems may include a lightning arrester and a meter-based or panel-mounted surge protector at the incoming power service. Plug-in or point-of-use protectors should be used to protect sensitive and critical equipment. Devices tied to phone or network lines should use surge protectors with protection ports designed for phone and network connections. The purpose of the arrester is lightning protection only. The meter-based or panel-mounted protector can handle high-energy power surges that enter through the electric service. Small, plug-in protectors provide secondary defense at the equipment to guard against internal surges and surges that may come through non-electric lines.

In order for surge protection equipment to work properly, it is critical for facilities to have good, low-resistance grounding systems, with a single ground-reference point to which the grounds of all building systems are connected. Without a proper grounding system, surge protection becomes quite difficult. NLSI provides guidelines and recommendations for surge protection of buildings, as well as on-the-job tips. The National Electrical Code is a good source of information on grounding issues as well. Two other relevant standards were recently updated: NFPA 70E, Standard for Electrical Safety in the Workplace and NFPA-780, Standard for the Installation of Lightning Protection Systems.