Limiting Systems Damage From Lightningâ€”the Controversy Continues
Here comes another lightning season. As with seasons in the past, some dealers will take grounding precautions when installing systems, while others will not. Replacing lightning-damaged panels can generate additional revenue, but it can be offset by new and ever-increasing false alarm fines, ill will from customers and, in some cases, no municipality alarm response at all.
The installation of lightning suppression for low-voltage systems still remains an area of technical controversy and misunderstanding.
Lightning Can Damage Many System Parts
Living in central Florida, I have experienced some very severe lightning storms. It is not uncommon when conducting an annual inspection to find a magnetic reed contact from a door alarm or window alarm that has been welded shut by a secondary lightning strike. Check out alarm loop suppressors, such as the GRI CS-1 (www.grisk.com).
Residential and commercial low-voltage systems are becoming larger and more diverse. This provides increased risk to equipment damage from lightning. Security equipment manufacturers continue to express concerns about these risks, which have also recently been reflected in a new addition to NEC 2002, Article 800.40(A)(4), communication circuit section of the National Electrical Code, on primary residential grounding.
Another area that installers should become familiar with is NEC Article 250 on grounding. This information, however, can be confusing in that NEC does not specifically require the grounding of systems less than 50VDC. This has been the excuse that many use for not grounding alarm systems. We should, at least, allow the customer the opportunity to look at the big picture here (see table).
Know Thy Enemy: The Facts Behind Lightning
Some lightning facts: A typical strike delivers between 10,000A and 40,000A, generates temperatures as high as 50,000 degress C, has voltage levels of 6,000V to more than 100,000V and causes billions of dollars in property and equipment damage annually.
Other lightning facts that system installers should be aware of include: A lightning surge can travel as far as 40 miles. Lightning will find many paths to ground. Within milliseconds, these pulses can induce energy that can cause additional circuit damage. Each lightning strike can contain as many as 45 ground strikes. An average region in the United States can expect two to 30 strikes per year within a square mile.
Don’t leave your customers rolling the dice on these dangers. You should take the lead, inform them of what can be expected and what current technologies can help to prevent this damage, and even possible loss of life.
Find Solutions That Work for Your Clients
Many Authorities Having Jurisdiction (AHJs) now require the installation of aftermarket lightning suppression technology. False alarm ordinances, including the National Burglar and Fire Alarm Association (NBFAA) model fire alarm ordinance, now require that systems be grounded at least per the manufacturer’s instructions.
Suppose you have convinced your customer to purchase additional lightning suppression. To make this work, you need a good ground. There are several good sources for acceptable grounds. As a guideline, the impedance between your equipment and ground should not exceed 25 ohms, and, ideally, should be below 5 ohms.
Take Proper Measures to Ground Systems
Grounding system equipment should be done with at least a No. 14 solid conductor. Make sure runs are short and straight with smooth bends. Lightning likes to jump out of sharp wire bends. Any ground connections must be made with either exothermic welds, UL-Listed clamps, lugs or straps.
Good ground sources include a building or structural grounding electrode system. This can involve the steel building structure bonded to the metal rebar in the concrete foundation. This is sometimes referred to as Ufer Ground.
A metal water pipe that is buried at least 10 feet in the ground is another good option. Connect to the pipe within 5 feet of it exiting the ground. Be careful to avoid pipe sections using nonconductive PVC. Make sure that service meters have a bonding strap across them. Be sure not to use gas pipes.
When there are multiple ground locations in a system, they all should be bonded. Bonding connects multiple grounds with at least a No. 6 conductor. This forces all the equipment to be at the same voltage level when hit by a lightning surge and can minimize system equipment damage. Remember, a building should have only one grounding system. Check to see if the building has the UL lightning protection mark.
Disconnect the System to Foil Lightning
The best lightning protection of all is to completely disconnect all equipment just before a lightning storm hits. Several companies offer products and services that can do just that.
Bob Dolph is based in Orlando, Fla., and has served in various technical management and advisory positions in the security industry for 25 years. He is currently a training and products consultant. Check out his online technical Q&A column at www.securitysales.com.To share tips or ask questions about installation or troubleshooting, E-mail Dolph at [email protected].
Disclaimer: The information and advice presented in this article is made available in good faith, and is derived from sources believed to be reliable and accurate at the time of release. Before using such information, make sure codes, safety issues, and manufacturer’s specifications have been fully adhered to. The writers of this article and Security Sales & Integration magazine disclaim any liability from the use of this or any other information.
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