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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 PST

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.

Lightning Protection for the Farm

The cable form is now more popular than the rod. Cable is easier to install, because it is flexible, and it has fewer joints to interfere with the conducting of electricity (fig. 5).

Lightning Protection for the Farm

Install conductors to join air terminals in straight lines, along the face of the gables to the eaves and then down to ground connections (fig. 6). Avoid unnecessary bends. Do not use bends with curves of under 8- inch radius.

When copper or aluminum cable is used, make necessary joints with strong fittings that will permanently connect the parts without soldering.

Lightning Protection for the Farm

Fasten conductors with single- or double-nail strap fasteners. On masonry use brass screws set in masonry anchors (fig. 7). To make a neat and durable installation, space fasteners about 3 feet apart.

Metal roofs or building walls can serve as part of the conductor system only if there are no breaks in their construction that would prevent them from being electrical conductors.

Branch conductors, usually made of conductor material of smaller diameter, should connect all structural metal parts of the building with the main conductor system. Use branch conductors to interconnect roof vent pipes that are within 6 feet of any conductor, and also to interconnect stanchions, litter tracks, haytracks, guy wires, door tracks, and stationary farm apparatus to the main conductor system.

GROUND CONNECTIONS

Ground connections are of vital importance to the operation of the lightning-protection system. Make the ground connection properly; it is the key to the efficiency of the whole system.

At least two ground connections are usually needed for every lightning-protection system. They should be spaced as far apart as possible. They should also extend below and away from building foundations to prevent damage to walls from lightning discharge.

Lightning Protection for the Farm

Ground connections are made in one of four ways: By driving a copper-clad or galvanized steel rod at least 10 feet into the ground, or by stranding copper conductor cable and burying it in a trench, or by clamping copper conductor cable to a buried sheet metal plate (fig. 8), or to a water pipe. The chief requirement is to get the lightning-protection system into good and permanent connection with moist earth. Never try to ground a conductor by putting a short length of it into the earth; this does not give enough electrical contact.

Determine the character of the soil in which the ground is to be made. Test moisture conditions at various locations around the building, taking into consideration the dryness or wetness of the season at the time. Select the more moist locations for making ground connections.

Avoid soil or chemical substances that will corrode the ground connection. Heavily galvanized steel resists corrosion for long periods in soil. Copper and copper-clad steel resist corrosion indefinitely in soil that is relatively free from ammonia.

Do not use aluminum for ground connections; it corrodes in soil.

Do not paint ground connections. Painting reduces their electrical conductivity.

If it is not practical to reach permanently moist earth, increase the area of the ground connection by extending the metal horizontally under the soil, or by using several grounds extending radially away from the point of entry into the ground. Other alternatives are to increase the number of ground connections or to run a ground entirely around the building with all conductors connected to it.

Lightning Protection for the Farm

Where soil conditions do not permit driving or digging to a sufficient depth, make a ground by burying a copper cable in a trench running away from the building (fig. 9). For a depth of 5 feet make the trench 15 feet long; for a depth of 4 feet make it 20. Make shallower trenches proportionately longer.

Cover the trench floor with a 5-inch layer of pea-sized charcoal, which will help the grounding ability of the cable. Untwist the cable and spread the strands over the charcoal. Cover the strands with another 5 inches of charcoal and fill the trench in with soil. The ground may be improved still more by splicing another cable to the conductor cable near the point of entry into the ground, and then spreading these additional strands in the same or another trench.

Lightning Protection for the Farm

Connections to water piping where it enters a building generally makes the best ground available. Make connections to water pipes with a strong clamp (fig. 10). Individual deep-well casings are excellent for ground connections.

Connect aluminum conductor cable to copper or steel ground connections with clamps designed for the purpose; otherwise connections are likely to corrode. Make these conductor-to-ground joints within a foot of the ground level.

Use a wooden housing to protect conductors and ground connections from damage by livestock.

After the ground connection is installed and connected with the whole system, have it tested for electrical resistance. Any competent lightning-protection system installer has an instrument for testing grounds. The meter readings should be very low on the scale for a ground connection in good condition: under 5 ohms is excellent; between 5 and 25 ohms is very good; and between 25 and 50 ohms is good.

PROTECTION FOR LIVESTOCK

Livestock are usually killed instantly when they are near a fence that receives a lightning discharge. An ungrounded or improperly grounded wire fence can carry some of the electric current from the lightning discharge along its wires as far as 2 miles. Wire fences that are attached to trees or buildings are most likely to receive and carry lightning discharges, but any ungrounded wire fence with wooden posts, or steel posts set in concrete, is a hazard to livestock.

Ground wire fences to avoid this hazard. Use posts of galvanized steel at intervals of about 150 feet along the fence.

Lightning Protection for the Farm

Another way to ground wire fences is to use pieces of 1/2- or 3/4- inch galvanized steel rod or pipe. Drive these pieces about 5 feet into the earth alongside the wooden fenceposts at about 150-foot intervals. Allow a few inches of pipe or rod to extend above each post. Fasten these pipes or rods to the posts with pipe straps so that they touch all the fence wires (fig. 11).

PROTECTION FOR TREES

Trees are often ruined or severely damaged by lightning. This is hazardous because the lightning discharge is transmitted to nearby areas. Also, if the tree is sufficiently damaged it may fall on a building.

Trees that especially need protection are those that are higher than nearby farm buildings. Other trees that should be protected are those under which livestock usually shelter in a storm and those that are individually valuable.

Protect a tree by installing one or more 10-inch air terminals at the highest secure part of the tree and grounding them through conductors. Very large trees may need two conductors and several air terminals.

Mount the conductors with long-shanked screw fasteners to keep the conductors from contact with the tree when a lightning discharge is being carried in the system.

Where there is a small group of trees, only a few of the tallest need to be protected. If a grove of trees is available for the livestock, remove isolated trees from the pasture, or fence them off to prevent the stock from sheltering under them in a storm.

Lightning Protection for the Farm

To make a ground connection, dig a trench and bury the unraveled end of the conductor cable in it. Make the trench shallow near the tree to prevent damage to the roots. Make it slant downward away from the base of the tree so as to reach moist soil (fig. 12).

To protect the exposed part of the conductor from damage by the livestock, cover it with a wooden casing.

INSTALLATION

Generally, it will be necessary to have an expert plan and install a lightning-protection system. Few persons have the equipment and skill to install and to test their own lightning-protection systems. The farmer should know, however, what the proper materials are and the methods used in the installation.

Follow the work carefully, especially the ground-connection installation. All ground connections should be tested with special equipment to make sure that they are adequate for lightning-protection requirements.

Reputable contractors guarantee their work; many of them will inspect the installation periodically.

Use materials approved by Underwriters’ Laboratories, Inc. All such materials are clearly labeled.

Follow installation methods described in detail in the Code for Protection Against Lightning, published by the National Bureau of Standards, or in Installation Requirements for Master Labeled Lightning Protection Systems, published by Underwriters’ Laboratories, Inc.

Lightning Protection for the Farm

INSPECTION AND MAINTENANCE

Make a periodic inspection of your lightning-protection system to be sure it is in working order.

Look for bent, loose, or missing air terminals, broken conductor cables, and loose connecting clamps. If new construction has been added since the lightning-protection system was installed, check to see that it has been interconnected with the system.

PERSONAL SAFETY

Do not go outdoors or stay outdoors during thunderstorms unless absolutely necessary. If you are caught outdoors, seek shelter in a cave. You may also take shelter in a deep valley or at the foot of a steep cliff, but guard against being caught by flash floods following the storm.

If a shelter is not available, lie down in any low spot in the ground.

Do not stay near isolated trees, wire fences, or small sheds in exposed locations. Keep off hilltops and open pastures or fields.

If you are in a truck or an automobile, stay inside.

If you are indoors, and the building does not have a lightning-protection installation, keep away from fireplaces, stoves, and other metal objects.

Spotlight On: Crops & Soil

Barnyard Manure

Barnyard Manure

by:
from issue:

The amount of manure produced must be considered in planning a cropping system for a farm. If one wishes to manure one-fifth of the land every year with 10 tons per acre, there would have to be provided two tons per year for each acre of the farm. This would require about one cow or horse, or equivalent, for each six acres of land.

Winter Production of Fresh Vegetables

Winter Production of Fresh Vegetables

by:
from issue:

Any claim about winter production of fresh vegetables, with minimal or no heating or heat storage systems, seems highly improbable. The weather is too cold and the days are too short. Low winter temperatures, however, are not an insurmountable barrier. Nor is winter day-length the barrier it may appear to be. In fact most of the continental US has far more winter sunshine than parts of the world where, due to milder temperatures, fresh winter vegetable production has a long tradition.

Horsedrawn No-Till Garlic

Horsedrawn No-Till Garlic

We were inspired to try no-tilling vegetables into cover crops after attending the Groffs’ field day in 1996. No-tilling warm season vegetables has proved problematic at our site due to the mulch of cover crop residues keeping the soil too cool and attracting slugs. We thought that no-tilling garlic into this cover crop of oats and Canadian field peas might be the ticket as garlic seems to appreciate being mulched.

Syrup From Oregons Big-Leaf Maple

Syrup From Oregon’s Big Leaf Maple

by:
from issue:

There is a great potential in establishment of a seasonal “sugarbush” industry for small farmers of the northwestern states, particularly western Oregon and Washington. Five syrup producing species of maples are found mainly east of the Rocky Mountains. The Box Elder and the Big-leaf Maple are the only syrup producing maples of the Pacific Northwest. Properly made syrup from these two western maples is indistinguishable from the syrup of maples of the midwestern and northeastern states.

Cultivating Questions

Cultivating Questions: Follow-Up On Phosphorus

We like to think that the bio-extensive approach to market gardening minimizes the risk of overloading the soil with nutrients because the fallow lands make it possible to grow lots of cover crops to maintain soil structure and organic matter rather than relying on large quantities of manure and compost. However, we are now seeing the consequences of ignoring our own farm philosophy when we resorted to off-farm inputs to correct a phosphate deficiency.

Cultivating Questions Winterkilled Cover Crops for a Mild Climate Part 2

Cultivating Questions: Winterkilled Cover Crops For A Mild Climate Part 2

Finding just the right cover crop-tillage combination for crops planted the last half of June has always been a real challenge in our location. While surface-tilling mature rye and vetch in May works well for fall crops established in July and August, this cover crop-tillage combo does not allow enough time for decomposition and moisture accumulation for end-of-June plantings.

Fjordworks Horse Powered Potatoes Part 2

Fjordworks: Horse Powered Potatoes Part Two

These types of team implements for digging potatoes were the first big innovation in horse powered potato harvesting in the mid-19th century. Prior to the horse drawn digger the limitation on how many potatoes a farmer could plant was how many the farm crew could dig by hand. The basic design of these early diggers works so well that new models of this type of digger are once again being manufactured by contemporary horse drawn equipment suppliers.

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.

Of Peace and Quiet

LittleField Notes: Of Peace and Quiet

by:
from issue:

Walk with me for a moment to the edge of the Waterfall Field. We can lean on the gate and let our gaze soak up the mid-summer scene: a perfect blue sky and not a breath of wind. Movement catches your eye, and in the distance you see a threesome hard at work in the hayfield. Two Suffolk horses, heads bobbing, making good time followed by a man comfortably seated on a mowing machine. The waist high grass and clover falls steadily in neat swaths behind the mower. What you can’t help but notice is the quiet.

Seed Quality from Two Perspectives

Seed Quality from Two Perspectives

by:
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We are approaching this from a seed quality standpoint, not just a seed saving one. Saving seed is fairly simple to do, but the results from planting those seeds can be very mixed; without a basis of understanding of seed quality, people can be disappointed and confused as to why they got the results they did. Both the home gardener and the seed company must understand seed quality to be successful in their respective endeavors.

Ginseng Culture

Ginseng Culture

U.S. Department of Agriculture Farmer’s Bulletin No. 1184 Issued 1921, Revised 1941 — The evident preference of the Chinese for the wild root and the unsatisfactory state of the general market for cultivated ginseng have caused grave doubts as to the future prospects of the industry. These doubts will probably be realized unless growers should strive for quality of product and not for quantity of production, as has been the all too common practice in the past.

Carrots and Beets The Roots of Our Garden

Carrots & Beets – The Roots of Our Garden

by:
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Carrots and beets are some of the vegetables that are easy to kill with kindness. They’re little gluttons for space and nutrients, and must be handled with an iron fist to make them grow straight and strong. Give the buggers no slack at all! Your motto should be – “If in doubt, yank it out!” I pinch out a finger full (maybe 3/4” wide) and skip a finger width. Pinch and skip, pinch and skip, working with existing gaps and rooting out particularly thick clumps.

Swallow

Rotation As A Means Of Blight Control

Every farmer knows that when a crop is grown on the same field year after year, it becomes inferior in quality and the yield steadily diminishes.

Marketable Cover Crops

Marketable Cover Crops

by:
from issue:

Our cover crops have to provide the benefits of smothering weeds, improving soil structure, and replenishing organic matter. They also have to produce some income. For these purposes, we use turnips, mustard and lettuce within our plant successions. I broadcast these seeds thickly on areas where cover crops are necessary and let them do their work.

What We've Learned From Compost

What We’ve Learned From Compost

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Our compost piles will age for at least a year before being added to the garden. We have learned that the slow aging is more beneficial to the decomposition process as well as not losing nearly as much nitrogen to off-gassing as happens with the hot and fast methods. Another benefit is the decomposition is much more thorough, destroying weed seeds, pathogens and any unwanted chemicals much better in a slower composting setup.

Rice as a New Staple Crop for Very Cold Climates

Rice as a New Staple Crop for Very Cold Climates

by: ,
from issue:

If you were visiting Earth from some other planet and had to describe its inhabitants upon your return, you might say that the average person eats rice, and grows it as well, usually on a small scale. You’d be accurately describing the habits of over a quarter of the world’s population. Rice has a special story with an exciting chapter now unfolding in the northeast USA among a small but growing group of farmers and growers.

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