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Lightning Protection Systems for under a Dime 

 

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by David Barron

When I was growing up in the upper Midwest, I remember very clearly visiting my grandfather's farm in Grays Lake, Illinois.  I was told prior to his death that he was not only a farmer but also a J. I. Case Equipment dealer. He had a very large three-story barn where he kept his tractors and equipment.  His business was known as Barron Implement.  As I grew up, I remember the unusual vertical rods on top of his barn and other wooden yard structures.  One day I asked my father what they were for, and he told me the following story.

First, he said that when he was a young boy, the glass balls on the rods were targets for his .22 caliber rifle -- until he got caught!  My father emphasized that his father got rather angry for shooting the balls off his lightning rods!  Gee, I wonder why?  He then told me that the rods were part of a lightning protection system which was installed on the buildings to protect them from lightning damage, mainly fire.  When I asked about the glass balls, he said that they were indicators that a lightning rod had been hit by lightning.  The rod would super heat and cause the glass ball to shatter, thus becoming an indicator of a strike and to check the system for damage.  These colored glass balls were not merely ornamental, but a vital element in the protection system.

These systems had always intrigued me and in my early modeling years, I installed them on the roofs of my scale structures.  In some NMRA contests and in a few published pictures, I have seen these rods installed on other models, some of them properly and others improperly.  In an effort to get the best information available about lightning rods, I contacted one of the leaders in the field, Mr. Douglas J. Franklin, Vice President (and descendent of Benjamin Franklin), Thompson Lightning Protection, Inc., of St. Paul, Minnesota.  Mr. Franklin provided all the diagrams from his catalog.  I also consulted my local Internet service and did a search for more information. 

First of all, let's discuss a little about lightning.  Lightning is a short lived, high current electrical discharge in the atmosphere, which can occur between clouds, cloud to air, and in its most destructive mode, cloud to ground.  Lightning is responsible for millions of dollars worth of damage every year to both forests and civilized areas, just in the United States!  It is further responsible for between 200 to 500 deaths per year, just in the United States.  Basically what happens is that buildups of negatively charged free electrons exist in the atmosphere.  Their invisible release along a specific path, known as stepped leaders, occurs when a discharge takes place near a cloud base.  The negatively charged step leader works downward to a point approximately 150 feet or less above the ground where another stepped leader from the ground, a building, tree, or other protruding objects, reaches up to meet it.  At that point, when the two leaders meet, the visible lightning is produced.  Several strokes of lightning can occur along this path until the charge center as the base of the cloud has dissipated.  The thunder that we hear is really a shock wave caused from the intense and explosive heating and expansion of the air along the discharge path.

During the 1700's, Benjamin Franklin was doing his famous "fly the kite in the storm experiments."  By 1749, he had suggested the use of lightning protection equipment in the form of metal rods for building and other structures.  Ben's theory was that if a metal rod was placed at the highest point on the structure and grounded by a low resistance cable, lightning would strike the rod and pass harmlessly along the system and into the ground.  Ben went on to say that a rod's area of protection was equal to a cone-shaped area with its base equal to the height of the rod itself.

Well, now that we know a little about lightning, how do we model a protection system on our scale buildings?  

Several different applications can be used --  from just cutting off the head of a straight pin and sticking it into the apex of roofs to a full fledged model of a lightning protection system.  I suggest using a K& S .020 solid brass rod and super gluing either Clover House #39 or Sierra Scale Models #120 white or colored insulators (glass beads) midway on the rod or air terminal. Figure 1 shows a copper or aluminum class 1 air terminal with threaded mounting pin.   This will provide several very realistic rods for less than a penny. 

Rod w/insulator.

Figure 1. Rod w/insulator.

Several different rod designs are offered from the Thompson Lightning Protection, Inc.  All of these designs, some as old as the turn of the century, have some form of grounding cable attachment points.  A sample is shown in Figure 2.  Some designs are for flat structures, some for peaked roofs; others are for stacks and chimneys.  Grounding cables can be simulated using waxed thread, wire, or monofilament line.  Connect all rods together and continue down to and attach to a copper ground rod.  The standard grounding rod is anywhere from 1/2 inch to 3/4 inch in diameter and up to twelve feet long.  I suggest using the K&S brass rod for this.  

Mounting base.

Figure 2. Mounting base.

The glass balls were used exclusively up to the 1940's.  After that, plastic balls became common, and few manufacturers continued producing the glass balls.  Some of the balls were hand blown, as the Polar Star (Figure 3), which dates back to 1916.  They were five inches in diameter and fit a 5/8" lightning rod.  They came in transparent amber, opaque blue, transparent green, transparent red, and opaque white.  

Polar star.

Figure 3. Polar star.

Today, an increased demand for glass balls has resulted in complete new designs.  Thompson offers these new glass products in transparent amber, transparent blue, transparent dark green, transparent ruby red, and opaque white.  Now, the balls come in two hemispheres and are plastic, which are put together face to face on the rods.  The two halves can be of different colors, resulting in an infinite number of color possibilities.  The plastic balls are set together, (Figure 4 illustrates a skyline plastic ball with ribbed style). 

Skyline plastic balls.

Figure 4.Skyline plastic balls.

They are made of a tough weather-resistant and fade-resistant styrene plastic and are almost indestructible -- purely decoration.  They come in many colors also -- sky-blue, transparent red, golden yellow, silver gray, transparent green, and snow-white. The glass balls were held in place on the lightning rod with a ball support ring, plastic balls fitting tightly over the rods. That ring is really nothing more than a thick metal washer device, with setscrews to tighten them down on the rod.  Then, a special hold down washer is used to prevent the balls from blowing off the lightning rods.  A note should be made that at no time were holes drilled in the rods or pins installed for this application because heating and cooling could cause the pins to become loose. Then, they would fall out causing the indicator balls to fall and break.  A good simulation of these support rings and hold down washers can be made by cutting a short section of insulation from an insulate wire and putting it above and below the glass bead. 

By now if you have followed this article and studied the drawings, you have become an "expert" in the lightning and model lightning protection field.  Since you know the dangers of not protecting your structures, you should either add these items or show some structures with lightning damage!  You could start a new industry on your pike for selling lightning protection equipment or have some men either repairing or installing a new system on one of your buildings.

Source

  • Franklin Lightning Protection Inc., St. Paul, Minnesota

Click ARTICLES to read other techniques for model railroading.

 Sierra Scale Models is owned and operated by Dave Barron, an NMRA Master Model Railroader. If you have questions about the products, send a message to David Barron or call 813-907-3343.