When Lightning Strikes
Years ago, electro-mechanical controllers and hydraulic systems were somewhat immune to lightning or electrical surges. With the advent of solid-state control products and electrically actuated solenoids, however, the need for improved surge protection began to increase. Even then, it was assumed that a certain amount of equipment replacement was the inevitable result of a severe lightning storm. But times have changed and so have customers' expectations.
Property owners and grounds managers have tired of the cost and manpower required to replace solenoids, as well as the landscape damage caused by lighting strikes. Troubleshooting lightning damage is frustrating and painstaking, as it can show up sporadically over a long period of time. The challenge for manufacturers is how to balance the cost vs. benefit of developing surge protection for products within a competitive price range.
Developing surge protection in control products is one key element; however, following recommended grounding techniques during installation is equally important to ensure consistent product performance over a longer period of time — keeping everyone happy.
Most control products incorporate lightning protection devices that create a short circuit path to ground, thus limiting the power surges caused from utility companies and, most intensely, from lightning. In order for the energy to be discharged into the ground (instead of the equipment), a proper path to the earth must be designed. With a properly designed grounding circuit, the frequency and severity of damage to the electronic equipment is dramatically reduced.
According to Vince Nolletti, vice president of irrigation operations for Paige Electric Co., LP, and co-author of the American Society of Irrigation Consultants (ASIC) Guideline for Earth Grounding Electronic Equipment in Irrigation Systems, designing grounding circuits to protect electronic equipment is a scientific process that must be handled by qualified personnel. But it's effectiveness relies heavily on installation, so Nolletti recommend the following tips.
Do not use cheap electrodes. Use UL-listed or NEC-conforming electrodes with the largest possible surface area. Minimize the use of ground rods because they have very little copper surface area, detrimental inductance characteristics and a short service life.
A single electrode is usually insufficient to meet National Electrical Code requirements or to achieve desired grounding performance. When using multiple electrodes, space them out such that each electrode has its own area in which to dissipate lightning energy. Multiple ground rod systems do a good job for electromechanical equipment, but are not very effective in protecting electronic equipment. If you use them, install them in a straight line instead of in a triangle formation. Using more than three electrodes in one circuit increases costs while yielding only incremental improvements.
Try to minimize the number of bends and sharp turns in ground wires and electrodes. When turns are absolutely necessary, make sweeping bends with a minimum radius of 8 inches and a minimum included angle of 90 degrees. This is automatically accomplished if you pull the wire through a 1.5-inch or larger plastic sweep ell. Do not use metal fittings/conduit as they increase the inductance of the wire.
Never install grounding electrodes in the proximity of the wires (high voltage and remote control wire) and cable connected to the electronic equipment as this could re-inject the lightning energy into the system. Install the electrodes at least 8 feet away from the equipment and wires.
Electrodes must make contact with the soil in order for them to function properly, and soil conductivity varies drastically by soil type. Clay soils exhibit good conductivity, which allows the grounding circuit to dissipate lightning energy very efficiently. Loose soils suck as sand, gravel and rock have very poor conductivity and create a serious challenge and higher maintenance costs. But soil will not conduct electricity without moisture. Soil needs at least 15 percent moisture content for it to conduct electricity efficiently. It is imperative that an irrigation circuit is installed over the general area of the grounding circuit to ensure that moisture is there all the time. In sandy soils, you may need to install a small drip valve to maintain adequate soil moisture levels to ensure proper grounding protection.
Soil conditions can be so poor as to require soil amendment with ground enhancement or earth contact materials to improve the conductivity between the copper electrodes and the soil surrounding them. However, never use amendments such as salt, chemicals, coal and concrete because they corrode and drastically reduce the life of the grounding electrodes.
Use only 6-gauge solid bare copper wire to make connections from the electronic equipment to the grounding electrodes. Smaller sizes can be vaporized by lightning surges, which reach flows of over 100,000 amps. Also, you should never use coils of bare copper wire in grounding grids.
Make connections between ground wires and electrodes using the exothermal welding process, otherwise known as “Cadwelds.” These are kits that allow the permanent welding of components so that they do not require maintenance.
Conduct periodic maintenance checks on connections and grounding resistance with a ground megger at least once a year to ensure product longevity and performance.
Finally, the most important component of proper grounding is a circuit design based on sound engineering principles. (Complete guidelines and downloadable AUTO-CAD drawings of ground grids are available from the ASIC at www.asic.com.)
IMPROVEMENTS TO CONTROL PRODUCTS
Surge protection features incorporated in controllers themselves go hand-in-hand with proper grounding. There have been several advances in this equipment over the years, including adding larger metal-oxide varistors (MOVs) on both input and output lines. Designed to respond to the speed at which surges reach their peak current, MOVs quickly clamp the initial energy spike when it exceeds a safe level. The larger the MOV, the more effective the response.
Should a severe lightning hit occur, a higher level of protection comes into play in the form of surge protection pills or inductors. Even though these are slower to respond than MOVs, they have the ability to discharge higher levels of energy to the ground and away from the electrical components.
While most control products employ some type of lightning protection, these more advanced solutions can be offered as an option to meet the needs of high-risk regions of the country. Of course, with additional protection comes additional cost. But by offering differing levels of protection in the same product, users are not forced to pay for more protection than they need.
THE NEXT STEP
Installing a hydraulic system used to be the best way to protect valve-in-head sprinklers from being damaged during lightning storms; however, this is no longer the case. By enhancing the solenoids with surge protection, system components beyond the controller are being protected in even the most high-risk areas of the country.
A number of valve-in-head sprinklers on the market feature surge-protection in the solenoids. They range in protection levels, with products rated up to 20,000 volts. The higher-voltage rated products offer the most surge protection. Not only can these solenoids survive lightning seasons with no blow outs, they save countless man-hours, hundreds of replacement solenoids and much aggravation — all benefits that outweigh the increase in the cost. This success also has lead to further product development, including commercial-grade valves designed with same advanced-technology, high-voltage solenoid.
BENEFITS FOR CUSTOMERS
When manufacturers are investing in new technologies that make products better, it's the customer who wins. Technology costs are coming down, making it increasingly cost effective to provide high levels of surge protection — even in lower-end products.
Traditionally, irrigation design consultants have been faced with the cost/value relationship of products offering advanced surge protection. It has been a question of protection vs. replacement. However, as product design morphs to face everything Mother Nature throws at it, the result will continue to be greater protection for irrigation systems at all levels.
Greg Parker has worked for The Toro Co. (Riverside, Calif.) for 13 years. He is a registered landscape architect in the state of California and a 27-year landscape industry veteran.
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