As an electrical storm builds, various mechanisms create a stratified charge within the storm cloud, with an electrical charge at the base of the cloud. Since we are concerned primarily with cloud-to-ground lightning, we are concerned primarily with the charge on the base on the storm, as that charge induces a "shadow" of opposite charge on the surface of the earth beneath it.

 As the storm charge builds, so does the cloud base charge. Since like charges repel and opposite charges attract, the cloud base charge induces an opposite charge on the surface of the earth beneath it: it pushes away the same charge and pulls in the opposite charge. The cloud base charge attracts, or pulls, on the ground charge, trying to pull it off the surface of the earth. It is this tendency for the storm base charge and the ground charge to equalize through the intervening air which causes cloud-to-ground lightning.

 As the storm cloud travels over the earth's surface, it drags this ground charge along beneath it. When the ground charge reaches your facility, the storm cloud charge pulls it up on, and begins concentrating ground potential on your facility. If, before the storm cloud travels away, it manages to concentrate enough ground potential on your facility so that the difference in potential between the storm cloud base charge and your facility exceeds the dielectric strength, or resistance, of the intervening air, the air breaks down electrically, and a potential equalizing arc occurs; a lightning strike.

 Since we are concerned with lightning strikes to objects and structures on the surface of the earth, and some 95% of all ground strikes are negative cloud-to ground lightning, for the purpose of this discussion we will describe negative cloud-to-ground lightning.

 When the intervening air breaks down, the strike itself begins with the propagation of stepped leaders. Stepped leaders originate within the cloud charge, and extend in jumps of a hundred and fifty feet or so at a time towards the surface of the earth. These are the wispy, downward reaching branches of light you see in a photograph of a strike.

We see a lightning strike in two dimensions. Actually, the area of stepped leaders also has depth, so there is a field of stepped leaders working their way down toward the surface. When the stepped leaders reach to within about five hundred feet of the surface, the attraction between the stepped leader charge and the ground charge becomes so strong that objects on the surface of the earth begin to break down, and respond by releasing streamers of ground charge upward toward the stepped leaders. Streamers form off various objects on the surface: utility poles, fence posts, antennas, building edges, etc.

When a streamer and a stepped leader meet, the ionized channel becomes the path for the main lightning discharge. The other stepped leaders and streamers never mature. Occasionally, two or more will meet simultaneously, and forked or branched lightning will occur.

Once the ionized path is completed, the current discharge occurs. Although a lightning strike appears to be a single flash, it is actually a series of flashes. Lightning flashes on for approximately one one-thousandth of a second then shuts off for about two one-hundredths of a second, flashes on for one one-thousandth of a second then shuts off for about two one-hundredths of a second, repeating the process multiple times. When the potential difference is no longer sufficient to continue the discharge, the lightning strike ends.

There are four basic types of lightning damage:

• physical damage

• secondary effect damage

• electromagnetic effect damage

• damage caused by changes in ground reference potential

Physical damage is caused by current flow and heat.  A typical lightning strike in the United States conveys between 25,000 and 45,000 amps, with the higher amperage strikes occurring in the south, where the storms build higher.  Lightning is high current flowing over a short period of time.

The core temperature of a lightning channel is approximately 50,000 degrees Fahrenheit, or about five times the surface temperature of the sun.  During a strike, the temperature rises from the ambient temperature to a temperature approaching 50,000 degrees over a very short rise time.  It is this heat which causes the sap in a tree struck by lightning to turn to steam and expand, splitting the tree.  Concrete never quite dries out; there is always latent moisture in concrete.  When a concrete structure is struck, the latent moisture turns to steam, expanding and damaging the concrete structure. 

When the air surrounding the lightning channel is heated this rapidly, it expands in a shock wave.  This shock wave can damage a structure.  This is why lightning rods have a minimum length - top lift this shock wave off the roof of the protected structure.

The secondary effect of a lightning strike can cause arcing and induced currents. During a lightning strike, the point at which the strike occurs is relatively vacated of ground charge. The area surrounding the point of the strike remains highly charged, causing an almost instantaneous potential gradient across the area. The surrounding area releases its charge to the point at which the strike occurred, causing a flow of current.

This current flow can arc across any gaps in its path. If that arc takes place within a flammable material, it can cause a fire or explosion. If the arc takes place within a bearing, such as in a pump in a treatment plant, it can scar the bearing and cause premature wear. If it takes place on a circuit board, it can damage the circuit board.

The electromagnetic field effect is similar to nuclear blast EMP, and can induce currents in nearby wires or other conductors. The on-off-on-off action of a lightning strike causes the electromagnetic field surrounding the strike to expand and collapse with the series of flashes. This electromagnetic field motion can induce electrical currents in nearby conductors, including wires and electrical equipment.

Older vacuum tube equipment operated on relatively high voltages. Therefore, the vacuum tube was able to absorb a much higher voltage surge without damage.  When a vacuum tube which operates on a few hundred volts sees a one hundred volt surge, it is no big deal. When a microprocessor which operates on only a few volts sees a one hundred volt surge, it is a big deal. The current induced by electromagnetic effect can easily be sufficient to cause damage. In fact, microprocessors can be damaged by a nearby strike even if they are not in use or even connected to a power source.

This effect explains why lightning may strike a few hundred feet away from a structure and the telephone system in the structure stops working. Why? Obviously, the lightning energy did not enter the structure. The electro­magnetic pulse from the strike induced current into the telephone wiring into and within the building, damaging a microprocessor within the system and causing a system failure.

When the ground reference potential changes across a site, it can cause current flow through grounding systems.  Assume that the AC power service enters a structure at one location and is grounded at that location.  The telephone service enters the same structure and is grounded a different location.  Both feed into a computer.  The AC power service ground establishes the potential of the motherboard, and the telephone service ground establishes the potential of the modem board.  Current divides and takes all paths.  The amount of current flowing over any one path is proportionate to the surge impedance of that part vis-à-vis the surge impedance of all paths.  If lightning strikes near the structure closer to one service ground than the other, there will be a difference in potential between the two grounds.  This difference in potential will produce current flow.  Most of the current will flow through the ground under the structure (the lower impedance path).  However, some current will flow from one service ground, through the modem and computer, to the other service ground.  This current flow can damage the computer.

LIGHTNING PROTECTION: A THREE-PRONGED ATTACK

Integrated Three-Step System:

Based upon this experience, we have developed an integrated systems approach to environment optimization which may be tailored to any type of facility or operation in any part of the world. The Lightning Master approach consists of three steps:

• Bonding and Grounding

• Transient Voltage Surge Suppression

• Structural Lightning Protection

As you read through the various sections, you will notice that it is based upon the three step program. Each section begins with a narrative providing background information. The narrative is followed by cut sheets on products which we use to execute each part of our systems approach.

To implement our solutions-based approach, Lightning Master personnel will conduct a survey of your facility, provide you with a written report of our findings, design and recommend the optimum system solution, and, should you prefer the turnkey approach, provide and install the system we recommend.

We can also help you write specifications to assure effective and uniform practices at and between your facilities. Whatever you need, we can provide in a prompt, cost-effective package.

After you read through our information, please call us with your specific questions regarding our approach and how we would apply it to your type of application. We will be happy to discuss any aspect of our program, and, if you would like, meet with you at your convenience for an in-person presentation.