Lightning kills more people than tornadoes and hurricanes combined
Lightning information of interest for Engineers, Contractors and employees
to understand how to prevent fire and damage to buildings
Lightning will jump a mile through air to get to ground to neutralize the charge between the earth and the cloud. It is estimated to be 200 million volts with 30 thousand amps of current.
How to prevent damage to the building: The answer is to provide a path to ground for the lightning to follow that is better than air. Air is very high impedance; therefore, a ground rod is much better than air no matter the impedance or ground conductivity.
When lightning arcs, it is 50,000 degrees, and can cause a fire, so design factors are to prevent any arcing. When lightning travels through wood it can heat the sap and create steam that will blow the wood apart. We supply a wire for the lightning so it does not travel through the wood.
The National Fire Protection Agency designed a system many years ago and after analyzing failures it improved the National Standards so we have a system now that does not fail.
It seems some electrical engineers try to improve on the standards by saying we should test the system and meet certain resistance readings or use larger wire. The standards require that we install the components in a certain way for success but do not have testing standards. The standards tell us how many points and grounds to be used and where they are to be installed along with bonding requirements to prevent arcing. Standards require we use UL Listed components that are listed for a specific use.
Since the duration of lightning is a maximum of 20 microseconds it has very little chance of heating the wire. The standards all allow aluminum or copper wire but require different sizes depending on the building class.
The standards for lightning protection will prevent damage to the building but does not address damage from surges caused by lightning damaging electronic equipment. To protect electronic equipment, we look in the IEEE Emerald book. Basically, this book recommends a surge suppressor on every electrical panel and on all other lines coming into the building.
This article was submitted by Bob Turner, as a Lightning Protection Institute Master Installer for 25 years.
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