Key Definitions and Concepts in Lightning Protection

Located at the highest points on a structure, these are commonly referred to as lightning rods. They are constructed from copper or aluminum and can be as slender as 3/8" dia. and as short as 10" tall. Learn more.

A connection or fitting that interconnects the lightning protection system with parts of a structure that could become electrically energized during a lightning event. These include bonding plates, bonding lugs, and pipe clamps used to join metallic parts of the structure to the lightning protection system. Learn more.

Heavy duty multi-strand copper or aluminum cables that connect air terminals to one another and the roof network to the ground; can safely carry up to 3 million volts of lightning without damage. Learn more.

Electrical Resistance: Electrical resistance is the measure of how much a material opposes the flow of electric current through it. It is expressed in ohms (Ω) and depends on factors such as the material's composition, length, cross-sectional area, and temperature. In lightning protection systems, resistance plays a crucial role in determining how effectively electrical currents, including those from lightning strikes, can be safely directed away from protected structures. Lower resistance in conductors and grounding paths ensures better performance in dissipating electrical energy.

A ground rod, ground plate or ground conductor that provides electrical contact with the earth surrounding a structure.

Grounding System: A grounding system is a network of conductors and electrodes designed to safely direct electrical currents, including those from lightning strikes, into the earth. The primary function of a grounding system is to provide a low-resistance path for electrical energy to dissipate, protecting structures, equipment, and people from the harmful effects of electrical surges and lightning. In a lightning protection system, the grounding system includes ground rods, conductive plates, or ground grids that are buried in the soil, all interconnected to ensure efficient dissipation of electrical energy into the ground, thereby minimizing the risk of electrical shock, fire, or structural damage.

The evaluation of a building or structure's vulnerability to lightning strikes, including its size, height, geographic location, surroundings, physical construction materials, occupancy, succeptability to fire, and other potentially devastating consequences of an electrical storm. Check our lightning risk assessment calculator.

A lightning strike is a sudden discharge of electricity from a thunderstorm, where lightning directly contacts the ground or an object, releasing a large amount of electrical energy. Learn more.

NFPA 780 is the National Fire Protection Association's standard that provides guidelines and best practices for the design, installation, and maintenance of lightning protection systems to safeguard structures, electrical systems, and personnel from lightning-related hazards. This standard outlines requirements for components, bonding, grounding, surge protection, and inspection protocols to ensure the effective performance of lightning protection systems in various types of structures, including those housing explosives and other sensitive materials.

Sideflash: Sideflash is a phenomenon where lightning jumps or arcs from one conductive path to another within a structure, usually when there is a significant voltage difference between nearby objects, such as between a lightning protection conductor and a metal object or structural component. This unintended path can pose safety risks, including electrical shock, fire, or damage to equipment; proper bonding and spacing in lightning protection systems are critical to minimizing the occurrence of sideflashes.

Surge Protection Device (SPD): A Surge Protection Device (SPD) is an electrical component designed to protect equipment and systems from transient overvoltages, such as those caused by lightning strikes or power surges. It works by diverting excess voltage away from protected circuits to the ground, thereby preventing damage to electrical and electronic equipment, maintaining system reliability, and enhancing safety.

Electrical connection between an electrically conductive object and a grounded component of a lightning protection system that is designed to significantly reduce potential differences created by lightning strikes.

Also known as a building enclosure, the building envelope includes all the elements of a structure that separates the outside and inside environments. Based on a combination of architectural and engineering specifications, it provides resistance to air, moisture, seasonal temperatures, light, noise and other exterior environmental conditions. Learn more.

Also known as down leads, down conductors are cables or appropriately sized metal structural frameworks that allow the lightning to travel  between the roof-based lightning protection system to the grounding system.

Equipotential Bonding: Equipotential bonding is the process of electrically connecting all conductive parts within a structure to create a uniform potential, minimizing voltage differences that could lead to dangerous electrical currents. This connection helps to prevent electric shock and damage from lightning strikes by ensuring that all connected parts, including metal pipes, structural steel, and grounding systems, share the same electrical potential. In lightning protection systems, equipotential bonding is critical for reducing the risk of side-flashes and ensuring that lightning currents are safely directed to the ground. Learn more.

Also known as a ground loop, the ground ring is the in-ground system that carries the flow of electrical current away from the building and dissipates it into the earth and surrounding area. 

Lightning Protection System: A lightning protection system is an engineered network of rods, conductors, and grounding elements designed to intercept, conduct, and safely dissipate lightning strikes away from a structure, minimizing the risk of fire, damage, or injury. It works by providing a controlled path for lightning currents, preventing them from passing through or damaging the protected structure.

This is the old name for what are now called Air Terminals. Learn more.

A lightning flash is a visible burst of light produced by the discharge of electricity in a thunderstorm, typically consisting of multiple lightning strokes occurring in rapid succession within a short time frame.

Rolling Sphere Method: The Rolling Sphere Method is a technique used in lightning protection design to identify areas of a structure that are susceptible to lightning strikes. By conceptually rolling an imaginary sphere, typically with a radius of 46 meters (150 feet) representing the potential strike distance, around the structure, any part that touches the sphere is considered vulnerable and requires protection through the installation of lightning rods or other protective measures. This method helps ensure comprehensive coverage and placement of lightning protection components to effectively shield the entire structure.

The collective term for metal objects at the highest point of the lightning protection system.  This is typically the slender rods typically called Air Terminals, but it can also be a permanent metallic part of a structure, such as light pole or railing, so long as it is properly positioned and adequately sized. Learn more.

UL's standard for installation requirements for lightning protection systems. 

Zone of Protection: A Zone of Protection is the area within a structure or around an object that is shielded from direct lightning strikes by a properly installed lightning protection system, such as air terminals, conductors, and grounding components. This protected zone is defined by methods like the Rolling Sphere Method, ensuring that all vulnerable parts of the structure fall within the protective coverage provided by the lightning protection system. Learn more.