Wiring Lights: Lightning Protection Standards

Wiring lights various standards for product specifications and installation methods are published regarding lightning protection systems.

The National Fire Protection Association (NFPA) publishes "NFPA 780: Standard for Installation of Lightning Protection Systems" (2004).

This 45-page document provides requirements for the protection of people, buildings, and property against lightning damage.

The Lightning Protection Institute (LPI) publishes "Standard of Practice LPI.175," which establishes requirements for design, materials, workmanship, and inspection of professionally installed lightning protection systems. Underwriters Laboratories (UL) sets guidelines for the certification of systems materials and components in its publication, "Standard UL96A."

A wiring lights protection system provides a clear path for lightning to travel directly to the ground without causing injury or destruction to life or property.

It consists of three major components: (1) lightning rods, or air terminals; (2) grounding rods, or grounding terminals; and (3) copper or aluminum low-resistance conductor cable to connect the terminals.

Copper and aluminum components are used not only because they are excellent conductors of electricity, but also because they are highly resistant to corrosion.

Copper is preferred because it conducts electricity better than aluminum and less is needed to carry the same amount of current.

However, aluminum is necessary on an aluminum or steel roof because copper coming into contact with aluminum or steel can cause corrosion.

Nevertheless, even where aluminum is used, the grounding system must be copper.

Aluminum cannot be used underground and must be spliced into the grounding wire at least 18 inches above the ground [NEC Section 250.64(A)].

Before beginning any work, check your local and regional building codes to see whether you must satisfy any special requirements.

Also, be certain that all of the wiring lights protection components you install are listed by Underwriters Laboratories.

When designing a lightning protection system, always include a minimum of two grounding rods as widely separated as possible.

To calculate the total number of grounding rods, first measure the perimeter of your home, totaling the length of each exterior wall.

If the perimeter is 250 linear feet or less, use two grounding rods; between 250 and 350 linear feet, use three grounding rods; and between 350 and 450 linear feet, use four grounding rods, and so on.

Keep all conductor cable running horizontally or angled downward, and avoid sharp turns and U-turns.

To calculate the number of required lightning rods, measure the cumulative length of all roof ridges, including the garage roof and dormers.

Antennas, chimneys, weather vanes, cupolas, gables, and other roof projections must all be connected to the main cable using bonding lugs or cable connectors. Most importantly, make certain that the entire wiring lights lightning protection system is well grounded.

If only part of a system is grounded, lightning may flash sideways between grounded metal components on the roof or within the building, setting fire to flammable materials.

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