Lightning protection

The National Board of Fire Underwriters reports that lightning is the top cause of farm fires. Lightning is also responsible for more than 80 percent of all livestock losses due to accidents and millions of dollars in damage to farm buildings and equipment annually.

A system that protects your family, livestock and farm property from lightning strikes prevents or significantly reduces these dangers. Lightning protection systems should be installed only by qualified individuals who have the necessary credentials and equipment. However, a working knowledge of the principles of lightning protection will help you to communicate with these experts and oversee the proper maintenance of your system once installed.

A quick primer

  • Lightning is an uncontrolled, massive electric spark with tremendous voltage and amperage.
  • Lightning always tries to follow the shortest, easiest path to earth, and often follows several paths simultaneously.
  • The basic principle of lightning protection is to provide a direct, easy path for the lightning bolt to enter or leave the earth without passing through a non-metallic or non-conducting part of the structure or other object.
  • An effective lightning protection system includes many essential parts.
  • Generally, a protection system for buildings must include air terminals, down conductors, secondary conductors, arresters and ground connections, with all system components linked together.
  • The most reliable choice is a Master Label System that meets minimum requirements established by Underwriter Laboratories Inc. (U.L).

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How lightning behaves

Lightning is a visible discharge of static charges that can occur within a cloud, between clouds or between a cloud and the earth. A build-up of opposite charges (one negative and one positive) separated by an insulating air gap can cause the charges to rush toward each other, producing a sudden release of energy. A lightning discharge will have 10,000,000-100,000,000 Volts and 1,000-300,000 Amperage. A bolt packs so much voltage that it may leap a mile or more through the air. Lightning strikes buildings or other objects because the materials in them provide easier paths to ground than the air. Lightning is more likely to strike on projecting objects such as tress, poles, wires or building steeples than on larger, flatter surfaces projecting to the same height or lower. Lone buildings are also primary targets.

When a lightning bolt uses a building or other object as an electrical conductor, it generally follows a metallic path to the ground. "Sideflashes" may also occur when current leaps from its main path to the plumbing, appliances, water lines, a person or an animal. Sideflashes are dangerous because they can ignite a fire or cause electrocution. Lightning can enter a building through a direct strike, by striking a metal object attached to the building, by leaping over to the building after striking a nearby tree, or by following a power line or ungrounded wire fence attached to a building. Utility distribution systems use multiple groundings per mile and other protective devices to help dissipate lightning strikes and send them to the earth.

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More about fencing systems

You can obtain a copy of the publication Installation and Operation of Fencers, Cow Trainers and Crowd Gates from the Wisconsin Farm Electric Council. This how-to publication explains proper grounding and lightning protection for fencing systems. To request a copy, visit Midwest Rural Energy Council or call 608-262-5062 in Madison.

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Components of a lightning protection system

(1) Ground-attached wire fence (2) extend system to an addition (3) (4) (5) run secondary conductors to litter, metal door and hay tracks (6) install terminals on cupolas, ventilators, etc. (7) provide at least two grounds for barn (8) tie in metal stanchions 9) install arresters on overhead wires

Lightning Protection System

(10) provide at least one terminal on each domed silo and at least two on each flat-roof or unroofed silo (11) ground silo (12) connect to metal water pipe; and protect all buildings — valuable or not — within 50' of barn.

A lightning protection system should be installed for all important farm buildings, including barns, loafing sheds, houses and other structures. Protection may also be warranted for trees, wire fences and minor buildings.

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A typical air terminal

A good lightning protection system protects all points where a bolt is likely to strike and all objects to which the current might sideflash.

The five key parts of a system are:

  1. Air terminals (lightning rods)
  2. Down (or main) conductors
  3. Secondary conductors
  4. Lightning arresters
  5. Ground connections or rods

Air Terminal

Air terminals, or lightning rods, are designed to take any lightning bolt that may strike in the immediate area. Installed at high points, air terminals are pointed metal rods or tubes. Proper height and spacing of the terminals depends on the building configuration. Terminals are installed along roofs and on all projections such as chimneys, flagpoles, towers, dormers, ventilators and water tanks. Down (or main) conductors conduct the lightning bolt safely from the point struck to the ground. They connect air terminals with each other and with grounds. Each down conductor should have a separate ground.

Secondary conductors connect metal parts of a building together. The electrical bond this creates keeps lightning from flashing across the gap between the metal parts. All secondary conductors are connected to the main conductors. Numerous metal parts that are part of or attached to a building may need this protection. Metal roofing is a common trouble spot if not properly grounded. Other examples include metal hay tracks, door tracks, troughs, storage tanks, stalls, stanchions, milking lines, water lines, pipes, conveyors, long metal ducts, concrete reinforcement and more.

Arresters protect a building's wiring system from the dangerous surges of electricity associated with lightning strikes.


Ordinary circuit breakers cannot handle a power surge caused by lightning. Arresters protect wiring and electrical equipment by diverting power from the hot wire and safely guiding it to ground. Each arrester is connected to the building's lightning protection ground system. Arresters can be used to protect expensive electrical equipment and solid-state control panels in grain drying systems, milking/feeding equipment and computers. Ground connections for the lightning system are essential, causing lightning charges to dissipate without causing harm. Proper grounding installation varies depending on the depth of the soil and its conductivity.

Proper grounding depends on the depth of the soil and its conductivity. In sandy soils, two or three ground rods are installed in parallel and connected.

All grounding conductors should be bonded together, including telephone and electric service grounds, antenna grounds, all underground metal pipes and lightning protection systems. This prevents dangerous sideflashes between grounding conductors that are close together.


For clay soils, one ground rod is often used. Ground rods are driven 10' deep and placed at least 2' from the foundation wall. In shallow topsoil, grounding can be achieved by stranding the conductor and burying it in a long trench or attaching it to a copper ground plate.

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Materials and installation

Materials used in lightning protection systems must resist corrosion. Copper and aluminum cable are the most common, while copper alloys and copper-clad steel are also approved materials. Aluminum conductors corrode when in contact with earth. They should terminate at least one foot above ground level and connect with corrosion-resistant, copper conductors using special bi-metal connectors or connectors with an oxidation inhibitor. In other situations, combinations of materials subject to electrolytic action should be avoided.

Proper installation is also critical, and should be done only by a qualified expert. Before you select an installer, check references and verify the installer's experience level with similar projects. Your insurance company may be able to recommend a qualified installer. To obtain approval from the Underwriters Laboratories Inc. for a Master Label, a special application form must be signed by the owner, the installer and the equipment manufacturer. If all materials and workmanship meet the minimum requirements established by the U.L., a Master Label identification plate will be issued directly to the owner.

If you have an older farm with an existing lightning protection system, consult an installer about upgrading the system to incorporate more modern materials and up-to-date lightning protection techniques. While no system can guarantee 100% protection against the unpredictability of lightning strikes, an effective lightning protection system can go a long way toward protecting your family, livestock, buildings and equipment from this hazardous weather condition. Lightning protection is a form of insurance no farm should be without.

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Maintaining your system

Even the best lightning protection system can become ineffective over time if it is not properly maintained. Remember to take these important steps, and consult your installer for additional maintenance pointers.

  • Inspect the system periodically for mechanical damage caused by equipment or livestock.
  • Check for corrosion of any system parts.
  • Check the fasteners that attach the down conductors to buildings. Aluminum down conductors should not be blowing in the wind.
  • Connectors to ground rods should be free of corrosion and should form solid connections.
  • Wire connections to buildings must not be damaged or severed.
  • If new electrical work is done on the farm, make sure all new installations are properly connected to the lightning protection system.

Just one weak link can cause a lightning protection system to fail. Promptly correct any problems that may compromise the integrity of your system.

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