Lightning protection system components

Friday, October 24, 2014

A lightning protection system consists of the following five parts: air terminals (lightning rods), conductors, ground connections (electrodes), bonding and lightning arrestors.

Air terminals, or lightning rods, are metal rods or tubes installed at every projecting high point of a building -- such as the peak, a dormer, a flagpole or a water tank -- to intercept a lightning bolt. Solid copper rods should be a minimum of 3/8-inch in diameter, and solid aluminum rods should be a minimum of 1/2-inch in diameter. Rods should extend between 10 and 36 inches above the projecting object.

Typically, rods are 10 to 24 inches long; extra support or a brace is needed for a rod that is more than 24 inches long.

The most effective spacing is 20 feet apart for rods that are less than 24 inches long or 25 feet apart for rods that are between 24 and 36 inches long. Additionally, a rod should be located within 24 inches of the end of any building ridge or projecting object. Strategic placement of rods on a structure ensures that lightning will strike the rods rather than another part of the building.

Conductors, which are copper or aluminum cables, provide the connection between the air terminals and the earth to direct the lightning strike deep into the earth where it can safely dissipate.

Choose copper or aluminum rather than a combination of the two because galvanic or chemically corrosive action can occur between the two elements. Main conductors connect all of the lightning rods with the down conductors and then connect to the ground connections.

Ground connections, or electrodes, provide contact with the ground to safely dissipate the lightning charge. A minimum of two ground connections should be used for most buildings; additional ones may be needed for larger structures.

The type of ground connection may depend on the conductivity of the soil in your area. Ground electrodes should be 1/2-inch diameter, 10-foot long copper-clad steel or solid copper rods driven at least 8 feet into the ground.

Bonding involves branch conductors that protect against sideflashes by connecting metal objects (such as ventilation fans, water pipes, and so on) with the grounding system. Common grounding can eliminate lightning sideflashes. Grounding is achieved when all electrical systems, telephone systems, and underground metal piping are connected to the lightning protection system.

Lightning arrestors provide protection against a strike entering your building through the electrical wiring system and thereby causing potential power surges that may result in severe damage to electrical devices. To provide the best possible protection, lightning arrestors should be installed on the building's exterior where the electrical service enters the building or at the interior service entrance.