This article is reprinted with permission from GMPro magazine, where it originally appeared in the November 2000 issue (page 46).  For other informative articles on issues that concern the greenhouse industry, go to GMPro’s website by clicking on the GMPro logo above.

By Jeff Woolsey

Lightning causes millions of dollars in damage to businesses each year and is the second leading cause of weather-related deaths in the United States. National Geographic (July 1993) reported that lightning lasts less than a second, yet produces more energy than all of the electrical utilities in the world combined during that instant.

With the proliferation of computers and microprocessor-based devices in many greenhouses, lightning protection has become more critical. How can you protect your business systems from such a powerful and unpredictable adversary? Do you really need protection? Is it time for you to move beyond simple power strips?

Installing lightning protection equipment involves high voltages and serious personal safety issues. Use the following information to help you understand and formulate a plan for lightning protection. When you decide to implement your plan, use the services of a licensed electrician or lightning protection specialist.

Do you need lightning protection?
Whether you need protection depends on the level of lightning exposure. Location is a huge factor. If your operation is in an area with sun-heated surfaces and plenty of warm, moist air, lightning will be very frequent. Obviously, the more lightning that occurs, the greater the opportunity for exposure to damage. Flash density maps, which show approximate lightning frequency, are available on the Web and will provide you with the lightning risk for your area.

Sample Flash Density Map
(thumbnail only, click the map for more detailed lightning flash information at www.glatmos.com)

10-year flash density map courtesy of:
Global Atmospherics, Inc.
2705 East Medina Road
Tucson, Arizona 85706
520-806-7498 or 800-283-4557 Fax: 520-741-2848 e-mail: sdenman@glatmos.com
website: www.glatmos.com

Another factor is the cost and sensitivity of your equipment.  Even in an area with very little lightning, there may still be opportunity for high exposure if your systems are vulnerable to lightning damage.  It only takes one strike near your facility to cause extensive damage.

Lightning’s strange behavior
To deal with lightning effectively, you must realize that it acts quite peculiarly. You might expect lightning to behave similarly to electricity, but it does not. Lightning is much more powerful. It creates destructive levels of energy in microseconds and exists at very high frequencies. Lightning needs to be handled very carefully.

Everything you do to protect your facility from lightning should:

• Be optimized for high-frequency energy.

• Be sized to handle the lightning energy expected for the application.

• Have a fast enough reaction time to be effective against lightning.

For example, lightning, because of its high-frequency nature, doesn’t easily pass sharp bends in wires. Your equipment installer may need to abandon some long-held practices to deal effectively with lightning’s strange habits. The installer should follow the surge suppressor installation instructions carefully.

Remember that you have only microseconds to react to a lightning strike. Cheap, low-quality devices cannot react quickly enough to be effective. This means that everything in your system must be optimal, not mediocre.  High-quality protection devices are mandatory.

What should you protect?
First and foremost, protect your electronics. Computers, servers, network hubs, modems, environmental controllers, fax machines and telephone systems should all be considered for protection. Lightning storms create powerful disturbances called transients, spikes or surges. These temporary excesses of electrical energy can come from a variety of sources other than lightning; however, lightning remains the most destructive. These transients must be controlled if you are to succeed in protecting your electronic equipment.

Most electronic boards and microprocessors operate on tiny amounts of energy, whereas lightning generates huge amounts. These two electrical systems should never meet.

To prevent this disastrous encounter, you must safely direct this dangerous energy around and away from your equipment. You can send the lightning directly where it will eventually end up -- into the ground. This is referred to as grounding.

Pay close attention to detail and be thorough. Too often with lightning protection, a lot of time, energy and money are lavished on the front door (e.g., the electric wires), while the back door (e.g., the phone lines) is left wide open. A computer can just as easily be damaged or destroyed through a phone line as it can through the electric wires.

Good grounding
Adequate protection requires good grounding. If your grounding system is not up to the job, don’t waste your time or money on surge suppressors. They won’t work because the protection devices get rid of the excess energy from the lightning by shunting it into the earth.

What constitutes a good grounding system? Realize that when your electrical service was installed, the grounding system was designed primarily with personal safety in mind, not lightning mitigation. However, the adjustments outlined below, when properly implemented, will continue to give excellent personal safety and outstanding lightning protection.

Superior lightning mitigation grounding systems have two things in common: low impedance (low resistance to the flow of alternating electrical currents like lightning) and a single-point of contact with the ground.

Ground impedance. Your grounding system’s impedance should be as low as possible. Your electrician should perform these checks and make adjustments if necessary (all of these items lower impedance for high-frequency energy like lightning):

* Verify tight, clean connections at all grounding points.

* Use sweeping bends in grounding wires (minimum 12-inch radius).

* If the ground conductor passes through a metallic sleeve (like a piece of metal conduit), make sure the sleeve is grounded.

* Use finely stranded wire. (Lightning’s high frequency causes it to flow over the surface of things; stranded wire has more surface area.)

* Use a grid of interconnected ground rods if necessary to lower grounding impedance in poor soil conditions.

Next, consider single-point grounding. If your facility is powered by a single electrical service, this is probably not an issue. However, many greenhouses use multiple services. If this is the case, consider this matter carefully. Each electrical service has its own grounding system to meet safety codes and these should remain as they are. However, data cables, network cables or environmental computer cables running through various service areas must not be grounded haphazardly. There can be thousands of volts difference between ground rods during a lightning event, so check with your electrician or lightning mitigation specialist for details on a single-point grounding system.

Basics of lightning protection
Now that you have a good grounding arrangement, you can begin to plan your actual lightning protection system. Most modern systems employ a layered approach. This involves several kinds of devices, strategically installed for optimal protection.

The devices you will install are known as surge-protection devices (SPDs) or transient voltage surge suppressors (TVSSs), which are different names for the same thing.

Your first line of defense is at the main service entrance panel. This is where the power lines actually enter the building. One great benefit of this first layer is it affords some protection to every electrical device in your entire facility. After specifying the correct TVSS, read the installation instructions and follow them carefully.

The next line of defense is at the branch panels, which are smaller panels fed from the main service panel. Any excess energy that gets by the first layer of your system can be further suppressed by this second layer.

If you have an especially sensitive device, like a server or computer, you can install your third layer right at the device. This will generally consist of either an uninterruptible power supply (UPS) with surge protection or a good quality surge-protected power-strip. There are also TVSSs specifically designed to protect a single sensitive circuit that your electrician can install.

Other entrance paths
You have now closed the front door on lightning strikes, so to speak. Next you must close the back. Consider other potential entrance paths, such as telephone lines. You can either install surge suppression at the telephone system’s main terminal (centralized-for larger telephone systems) or at each line (decentralized-for small systems).

Your telephone company can install centralized protection, if it hasn’t already (most larger phone systems are installed with lightning protection). For decentralized protection, plug the phone line into a good quality surge suppressor designed for phone lines first, then plug into the device, such as the modem. Many power-strip surge suppressors and UPSs come with telephone protection built in.

Next, look at any data cables you may have. These might be used with your environmental control system, computer networks or other applications. There are TVSSs made specifically for these applications. Install these exactly as recommended by the manufacturer.

Remember to check your system often, especially after a storm. If a lightning strike is especially harsh, your TVSS may have to sacrifice itself to save your equipment. Many surge-suppression devices have small lights to indicate if the device is working properly.

Cost of protection
How much will all this protection cost? The number of TVSSs and their exact configuration and cost will vary with each facility. However, you may be surprised to learn how reasonable the cost is. High-quality TVSSs for power and data lines start at about $150. UPSs are in the same price range, whereas you can buy an excellent quality power strip with surge suppression for $50 or less.

Get started now
So what are the benefits of installing protection equipment? There is more to gain than simply avoiding costs due to lightning damage. There is less downtime, less disruption of your operation and greater peace of mind knowing that you can get through a thunderstorm with your business systems intact. Don’t put it off any longer; start planning your lightning protection system today.