Lightning Protection With Lightning Rods
Lightning Protection Systems
By Timothy Thiele, About.com Guide
Spring and summer storms spawn thunderstorms which produce lightning. Lightning can cause severe damage to a home without the addition of lightning rods to funnel the full force of its destructive powers to ground.
A lightning strike occurs when a passing cloud filled with negative charges of electrical energy meet the positive charges in the earth. Moisture from the storm between the clouds and the ground cause the negative charges to move downward out of the clouds to the earth's surface meet the upward-moving positive charges from the warmer, dry air in front of the storm that causes a lightning bolt.
Lightning rods are a good addition to one's home to protect them from lightning strikes. Lightning strikes the earth and structures at extreme speeds and force. In fact, it travels to the ground at 150-foot steps. Lightning rods divert positive charges to meet the negatively charged strike when the lightning bolt gets within 150-feet of the the lightning rod. Lightning rods neutralize lightning strikes to lessen or eliminate the damage they may have caused. This eliminates the lightning from hitting the structure of the home.
Lightning rods are 10-12 inches long and are made from either copper or aluminum. These are great conductors of electricity because of their low resistance. These materials are also resistant to corrosion, with the exception of copper when added to metal or aluminum roofs.
The underground connection to the lightning protection system must be made with copper wire because underground connections should not be made with aluminum wire. Aluminum wire will corrode when placed in the ground. The National Electrical Code requires the aluminum wire connection be at least 18 inches above the ground [NEC Section 250.64(A)] with a bi-metal splice. This connects to an eight-foot copper ground rod at least two feet from th home's exterior wall. There must be a minimum of two ground rods installed to the system on opposite ends of the home, with one near the service entrance ground rod so it can be bonded to this ground rod. This ensures that there is a common ground between all ground rods. This should make the connecting copper wire length between the ground rod and aluminum cable approximately four feet long. Place the ground rods diagonally on either end of the house, not exceeding 100 feet between the two ground rods. If this distance is exceeded, additional ground rods must be added to ensure proper grounding.
The National Fire Protection Association (NFPA)has guidelines for product installations and specifications. In a 45 page article (NFPA 780:Standard For Installation Of Lightning Protection Systems 2004), it describes protection for people, building, and property from lightning damage.
Attach the lightning rods to the peak areas of the home. Route the conductor cables, either made of copper or aluminum, between the lightning rods and bond to any TV towers, antennas, vents, heating exhaust flues, stacks, or any metal objects attached to the roof of the house. Place one lightning rod within 18 inches of the roof ridge ends and additional lightning rods no more than 20 feet apart. On flat or sloped roofs, lightning rods should be installed no more than 50 feet apart.
Be certain that the system you install is UL approved. The Underwriters Laboratories (UL) sets their own guidelines (Standard UL96A) for certifying the system materials and lightning protection system components used via their publication.
No comments:
Post a Comment