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How Experts Thwart Lightning
May 1952 Popular
Science
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May 1952 Popular Science  [Table of Contents]
Wax nostalgic about and learn from the history of early
electronics. See articles from
Popular
Science, published 1872- |
Benjamin Franklin is credited for coming up with the lightning arrestor scheme based on his famous experiments which ultimately determined that lightning was a form of electrical discharge*. He observed that during intense lightning storms around Philadelphia, the tallest buildings were usually the ones most likely to be struck - and often precipitating significant conflagrations upon itself and spreading to adjacent structures. Being certain that lightning was caused by a very large difference of voltage potential and the subsequent dielectric (air) breakdown with an ensuing very large current flow, he theorized than providing a safe pathway for the current to flow could spare the structure. To test his theory, Ben (his friends call him "Ben") installed pointed vertical rods at the highest point on the building and ran a conductor (likely an iron wire) down to Earth ground. Amazingly, when a bolt of lightning struck the rod, the current was safely shunted to ground rather than igniting the building. People quickly adopted the scheme and set about installing similar lightning protection systems on tall buildings. After that, only the shortest buildings burned during lightning storms (not really - I made that up). According to the Lightning Protection Institute**, the jury is still out on whether lightning rods help prevent strikes by lowering the voltage potential between the cloud and "ground." I'm in the camp that believes it does.
* Contrary to ignorant claims, Franklin did not "invent" electricity.
** While reviewing their material for tips about a solar panel installation I'm helping with on a neighbor's barn, I found an error in the part of the text and in an illustration, which they fixed. I'll be posting a writeup on the project once it is complete.
How Experts Thwart Lightning
Ten-inch rods are only things that are visible from front. Cables all go down the back way.
A house is ready to shrug off the mightiest bolts from the skies when they finish installing rods and grounding pipes and wires.
PSM Photos By W. W. Morris
Every year lightning sparks fires that destroy more than $52,000,000 worth of property in the U.S. In rural and suburban areas it is the No. 1 firebug. Cities are less hard hit, but throughout the nation, lightning is second only to defective flues as a cause of fires in homes.
You can't stop lightning but you can give your home better than 99-percent protection with a properly installed lightning-rod system. The photos on the next three pages show an expert installation by the Woods Lightning Protection Co., Shelton, Conn., on the Long Hill, Conn., home of architect A. J. Hawley.
Lightning strikes when static electricity jumps the air gap between earth and a cloud. The electricity wants only to discharge itself and seeks the easiest path. Lightning rods perched on the high points of a building offer it an attractive road.
Lightning rods were invented by Ben Franklin just 200 years ago. They haven't changed much since then, but modern installers have added a whole bagful of tricks for concealing rods, cables and links so that they won't mar the appearance of a building.
See lightning-protection photos.
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Fig. 1 - Cable is strung along roof and down both ends of house. Truck-workshop carries fitting to suit all structures.
Fig. 3 - Lightning Rod, called "air terminal," is threaded into saddle and leveled. Copper rods are lead coated to resist chimney fumes.
Fig. 5 - Two Terminals are needed on this chimney. Rule is that rod must be less than two feet from any corner. Rods are cabled together.
Fig. 7 - Roof Vent is interconnected, or "cross-bonded," too. Metal like this acts as lightning rod but would carry charge into house.
Fig. 9 - Tee Connector joins main cable with branch that goes through cellar wall. Downspout has been unhooked, moved to one side.
Fig. 11 - Ground Bar, a 10-foot copper rod, is driven with an electric hammer. It is joined to cable below ground as shown on next page.
Fig. 13 - Cellar Branch Cable is bonded to water pipe. Clamps, tees and connectors are specially made, can stand 2,000-pound pull.
Fig. 15 - Girder and supporting columns are bonded into single ground system by copper strip bolted to threaded end of stud. |
Fig. 2 - Ridge Saddle nailed to peak will hold rod. Underwriters' Laboratories sets rules for number of rods and spacing.
Fig. 4 - Chimney is Drilled for lead anchors that hold masonry saddle. Chimneys, favorite lightning targets, are always rodded.
Fig. 6 - TV Antenna Mast is connected to rod circuit with copper strip. Cable, 32-strand, 17-gauge copper, can handle any stroke.
Fig. 8 - Cable goes under eave. One man pulls it tight while another nails and clamps it. First paint job will hide it completely.
Fig. 10 - Wood Filler seals hole where tee goes through wall. When downspout is replaced, it will hide the cable.
Fig. 12 - Ground-Bar Clamp links cable and rod a foot or so below ground. At least two grounds are used; this house got three.
Fig. 14 - Powder-Operated Gun shoots a threaded stud into steel girder for ground connection. Metal must be interconnected.
Fig. 16 - Drains are tied into circuit in cellar. Plumbing is cross-bonded at several places to by-pass any high-resistance joints.
Fig. 17 - House Wiring - already grounded - is bonded to complete circle. Now neither static nor lightning can spark metal. |
Lightning Protection Articles on RF Cafe
- TV Antennas Invite Lightning to Strike - October 1960 Radio-Electronics
- Protect Against Lightning - July 1955 Radio & Television News
- Mac's Radio Service Shop: A Little Lightning - July 1948 Radio News
- How Experts Thwart Lightning - May 1952 Popular Science
- Lightning Protection & Safety Resources
- Anatomy of a Lightning Bolt - March 1973 Popular Electronics
- Facts About Lightning Protection - July 1959 Electronics World
Posted September 6, 2023
Copyright: 1996 - 2026 |
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