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Small Farmer's Journal
PO Box 1627
Sisters, Oregon 97759
800-876-2893
541-549-2064
agrarian@smallfarmersjournal.com
Mon - Thu, 8am - 4pm PDT

Lightning Protection for the Farm

Lightning Protection for the Farm

U.S. Department of Agriculture, 1959
by Harry L. Garver, agricultural engineer, Agricultural Engineering Research Division, Agricultural Research Service

Lightning is a particularly dangerous threat on the farm.

Every year over 400 persons are killed and over 1,000 are injured by lightning in the United States. Nearly all of these fatalities and injuries occur in rural districts.

Lightning is a major cause of farm fires. In Iowa from 1930 to 1947, fires started by lightning caused an average annual property loss of over $160,000.

Livestock and trees are also major victims of lightning damage.

Lightning protection can save the farmer money in two ways: By preventing loss of life and property, and by reducing the cost of his fire insurance.

THE NATURE OF LIGHTNING

Lightning is electricity that has both high amperage (rate of flow) and high voltage (pressure).

High voltage enables lightning to travel great distances through the air. High amperage is the main reason for lightning’s destructive power.

Experiments have proved that a charge of electricity must have a thousand times the voltage of household current to travel, or jump, just 1 foot through the air. Lightning, therefore, which usually travels over 2,000 feet between cloud and earth, must have extremely high voltage. But high voltage without large amperage is relatively harmless. The amperage of lightning discharges between clouds and the earth sometimes reaches 200,000 amperes or more.

Lightning follows the line of least resistance. The air through which lightning must pass between clouds and the earth is an insulating material of high resistance. Materials used in building construction have less electrical resistance than air. When such materials lie between the clouds and the earth, lightning naturally goes along the line of low resistance that they provide.

Lightning-protection systems for buildings give lightning ready-made lines of low resistance. They do this by providing unbroken bodies of material that have lower resistance than any other in the immediate neighborhood. A protection system routes lightning along a known, controlled course between the air and the moist earth. Well-installed and maintained, a lightning-protection system will route lightning with over 90-percent effectiveness.

Lightning Protection for the Farm

PROTECTION FOR BUILDINGS

Lightning-protection systems for buildings consist of three parts—air terminals (“rods” or “points”), conductors, and ground connections (fig. 1).

All materials used in lightning-protection systems should comply with the specifications of the Code for Protection Against Lightning published by the National Bureau of Standards.

Lightning Protection for the Farm

AIR TERMINALS

Air terminals are rods or tubes of metal (fig. 2) that are installed at every projecting high point of a building, such as roof peaks, chimneys, dormers, ventilators, gables, flagpoles, towers, and water tanks.

Terminals are manufactured in various lengths, but usually measure between 10 and 24 inches from tip to base. When terminals are made of copper tubing, they should be at least 5/8 inch in diameter and have a wall thickness over 0.032 inch.

Space the terminals along roof ridges, railings, and parapets according to the length of the terminals. (Recommended spacing also applies to metal-covered roofs.) If they are less than 24 inches long, space them less than 20 feet apart. If they are between 24 and 60 inches long, space them no more than 25 feet apart. There should be a terminal within 2 feet of each gable end of any roof.

Lightning Protection for the Farm

Short terminals — usually 10 inches long — are satisfactory for projecting parts of a building. They are usually clamped directly to the conductor cable. Longer terminals have bases that are attached to the building, and the conductors are clamped to the bases. Air terminals over 18 inches long are usually supported by metal tripods (fig. 3). Wind, snow, and ice seldom damage well-erected air terminals. Do not mount ornaments and weather vanes on air terminals. They may weaken terminal mountings.

Lightning Protection for the Farm

Air terminals on chimneys must be coated with lead to prevent corrosion from smoke fumes. They should project 10 to 24 inches above the top of the chimney (fig. 4).

Silos and towers with peaked tops need 1 or more air terminals; those with flat tops need 2 or more.

CONDUCTORS

Conductors are the parts of lightning-protection systems that connect air terminals with grounds. They are made of any good electricity-conducting material that will stand exposure to weather. Aluminum or copper is now used in most installations, instead of the once-common galvanized steel. Aluminum and galvanized steel corrode and lose strength in salt air. Do not use these materials for conductors where salt air is common.

The conducting capacity of a conductor depends on its weight. The minimum acceptable weight, per thousand feet, is: Copper, 187.5 pounds; aluminum, 95 pounds; and galvanized steel, 320 pounds.

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Spotlight On: Book Reviews

Work Horse Handbook

Work Horse Handbook

Horses are honest creatures. And, what I mean by honest is that a horse is almost always true to his motivations, his needs, his perceptions: if he wants to eat, if he needs water, if he perceives danger. He is incapable of temporarily setting aside or subverting his motivations to get to some distant goal. This is often mistaken as evidence for a lack of intelligence, a conclusion which says more of human nature than equine smarts. What it means for the horse is that he is almost never lazy, sneaky or deceptive. It is simply not in his nature.

Starting Your Farm

Starting Your Farm: Chapter 3

What goes with the sale? What does not? Do not assume the irrigation pipe and portable hen houses are selling. Find out if they go with the deal, and in writing.

An Introduction To Farm Woodlands

The farm woodland is that portion of the farm which either never was cleared for tillage or pasture, or was later given back to woods growth. Thus it occupies land that never was considered suitable, or later proved unsuitable, for farm enterprises.

Livestock Guardians

Introducing Your Guard Dog To New Livestock And Other Dogs

When you introduce new animals to an established herd or flock, you should observe your dog’s reactions and behavior for a few days. Since he will be curious anyway, it is a good idea to introduce him to the new animals while he is leashed or to place the new animals in a nearby area.

Barbed Wire History and Varieties

Book Excerpt: The invention of barb wire was the most important event in the solution of the fence problem. The question of providing fencing material had become serious, even in the timbered portions of the country, while the great prairie region was almost wholly without resource, save the slow and expensive process of hedging. At this juncture came barb wire, which was at once seen to make a cheap, effective, and durable fence, rapidly built and easily moved.

"Work Horse Handbook, 2nd Edition" by Lynn Miller

Draft Collars and How To Size Them

It is difficult to accurately measure a horse’s neck without fitting. In other words, there are so many variables involved in the shape and size of a horse’s neck that the only accurate and easy way to size the neck is to use several collars and put them on one at a time until fitting is found.

Art of Working Horses Another Review

Art of Working Horses – Another Review

by:
from issue:

One could loosely say this is a “how-to” book but it is more of an “existential” how-to: how to get yourself into a way of thinking about the world of working horses. Maybe we need to explain what a working horse is. A working horse is one, in harness, given to a specific task. So, in that context, the book illustrates the many ways Miller has worked with his equine partners over the years – helping them understand what he wants them to do, as both work together to create relationships that help achieve desired goals.

Starting Your Farm

Starting Your Farm: Chapter 4

Assuming that you’ve found a farm you want to buy, next you’ll need to determine if you can buy it. If you have sold your property, and/or saved your money, and have the means to buy the farm you are sitting pretty. If you do not have the full price of a considered farm, in cash or any other form, you will likely have to look for financing.

Audels Gardeners and Growers Guide

How to Store Vegetables

Potatoes may be safely stored in bits on a well drained spot. Spread a layer of straw for the floor. Pile the potatoes in a long, rather than a round pile. Cover the pile with straw or hay a foot deep.

The Horsedrawn Mower Book

Removing the Wheels from a McCormick Deering No. 9 Mower

How to remove the wheels of a No. 9 McCormick Deering Mower, an excerpt from The Horsedrawn Mower Book.

Starting Your Farm

Starting Your Farm: Chapter 2

How do you learn the true status of that farm with the “for sale” sign? Here are some important pieces of information for you to learn about a given selling farm. The answers will most probably tell you how serious the seller is.

How To Prune a Formal Hedge

How To Prune A Formal Hedge

This guide to hedge-trimming comes from The Pruning Answer Book by Lewis Hill and Penelope O’Sullivan. Q: What’s the correct way to shear a formal hedge? A: The amount of shearing depends upon the specific plant and whether the hedge is formal or informal. You’ll need to trim an informal hedge only once or twice a year, although more vigorous growers, such as privet and ninebark, may need additional clippings.

Storey's Guide to Keeping Honey Bees

Storey’s Guide To Keeping Honey Bees

It is well known that the value of pollination and its resultant seed set and fruit formation outweigh any provided by honey bee products like honey and beeswax.

Aboard the Planetary Spaceship

Aboard the Planetary Spaceship

SFJ Spring 2016 Preview: Edward O. Wilson’s new book, Half-Earth: Our Planet’s Fight for Life, offers a plan for the problem of species extinction: the dominant species, man, must hold itself back, must relinquish half the earth’s surface to those endangered. It is a challenging and on the face of it improbable thought, expressed in a terse style. But his phrases are packed because the hour is late.

Making Buttermilk

The Small-Scale Dairy

What kind of milk animal would best suit your needs? For barnyard matchmaking to be a success, you need to address several concerns.

Starting Your Farm

Starting Your Farm: Chapter 5

You might think that your new farm is fenced all wrong, or that a certain tree is in the wrong place, or that a wet area would be better drained, or that this gully would make a good pond site, or that a depression in the road should be filled, or that the old sheds should all come down right away. Well maybe you’re right on all counts. But maybe, you’re wrong.

Art of Working Horses Hunter Review

Art of Working Horses – A Review

by:
from issue:

Over 40 years Lynn Miller has written a whole library of valuable and indispensable books about the craft of working horses. He has helped beginners acquire the basics of harnessing and working around horses, and has led those further along to focus on the specific demands of plowing, mowing, haying and related subjects. But, in a fitting culmination, his latest book, The Art of Working Horses, raises its sights and openly ponders secrets at the heart of the work that may over time elevate it to an art.

A Short History of the Horse-Drawn Mower

A Short History of the Horse-Drawn Mower

Book Excerpt: The enclosed gear, late model John Deere, Case, Oliver, David Bradley, and McCormick Deering International mowers I (we) are so fond of had a zenith of popular manufacture and use that lasted just short of 25 years. Millions of farmers with millions of mowers, built to have a serviceable life of 100 plus years, all pushed into the fence rows. I say, it was far too short of a period.

Small Farmer's Journal

Small Farmer's Journal
PO Box 1627
Sisters, Oregon 97759
800-876-2893
541-549-2064
agrarian@smallfarmersjournal.com
Mon - Thu, 8am - 4pm PDT