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On Solid Ground
Golf Course Management
Scott Nesbitt
Golf course Superintendents association of America
"Proper protection from electrical quirks is vital to the operation of the sophisticated equipment that enhances today's golf course management practices."
Superintendents have always known that it's easiest to maintain a golf course that's built on good ground.
Now they are learning it's easiest to keep their course running smoothly if they make sure their high-tech equipment also has good ground-of the electrical variety.
Grounding in electrical terms means diverting electrical current into the soil where it can dissipate. The semi-circular hole in a standard alternating-current home wall outlet is a ground lead. It connects with a green or bare wire that runs to a grounding block in the fuse box. The grounding block is connected to two heavy wires-one connects with the home's water pipes, and another that goes to a metal rod driven into the soil outside the foundation. The white, or "neutral" wire also runs to the same grounding system.
In fact, there is only one "hot" wire in a wall outlet - the black one. The neutral line only carries power when there's an appliance plugged into the outlet.
In effect, the electric power that comes from utility companies uses the ground, literally, to complete the normal power circuit that is used everyday. This secondary, or green, grounding system provides a backup grounding system in case something goes wrong. If the hot wire gets exposed, such as when something accidentally slices through the power cord, that green safety ground is there is needed to bring the power safely back the ground.
Breaking new ground
The normal backup grounding system was first developed to prevent humans from being shocked, injured or even killed by stray voltage. Now, in the computer era, equipment designers are finding that a similar grounding system is critical to the health of microchips and other delicate electronic circuits that do so much of the work in systems that control irrigation, handle communications and monitor the weather. These systems can be "killed" by the same stray voltage that affect people. Someone hitting an irrigation controller with a golf car can release some serious high voltage that needs the conventional ground.
But there's also danger from much less powerful stray currents that a person can barely feel. A major culprit in microchip murder is transient voltage surge (TVS). This is a low-wattage, high-voltage jolt of electricity that appears spontaneously in wires that are near electromagnetic activity. It can be induced in the wires by a nearby lightning strike, or sent through the normal electrical system when a pump station motor is shut off. It can even appear when fluorescent lights are turned on and off.
Most computerized control systems come with a built-in surge suppresser that automatically diverts excess voltage into the ground circuit. These suppressers are designed to protect both the high-voltage power systems, and low-voltage circuits such as telephone lines and irrigation controllers. But surge suppressers can't do their job if they send stray current into a grounding system that offers too much resistance to low-power surges.
Standard grounding systems are designed for high-voltage systems - 120 volts AC or more. These voltages are high enough to punch through some substantial resistance that may exist in their grounding systems. As long as the ground offers less resistance than the resistance found in a high-voltage appliance, the grounding system will do its job.
Computers have extremely low internal resistance. They use gold-plated connectors and specially processed materials that reduce resistance. This is critical because electrical resistance creates heat (which is how a toaster works), which caused expansion and contraction of microelectronics components, and is a leading cause of failure.
If the computer's grounding system has more resistance than the computer, the TVS will seek, and often find, a way to blast through the computer's circuits on its way to the ground. That surge, though of short duration and low power, can be enough to turn the computer to toast.
Mother Earth
A fundamental part of all equipment grounding is some king of metal conductor that can divert uncontrolled electrical currents down, literally, into the ground. The planet itself is an active electrical reservoir that can absorb any stray voltage, whether a mammoth lightning bolt or a stray trickle from a faulty telephone wire.
It isn't enough that the conductor just touch the soil surface. Dry soil is an electrical insulator - not too different t from the ceramic insulators used on high-tension electrical lines. To be effective, the grounding system must put the metal conductor in touch with subsoil moisture - the water then carries the current away, spreads it around and dissipated it.
But while the principle of grounding is simple, the actual practice can be rather complicated.
Doug Colson, Northeastern field service manager for The Toro Co., says computer-controlled irrigation systems should have a grounding system with 10 ohms or less of resistance. a perfect connection has 0 ohms resistance, and a perfect insulator is said to have infinite ohms. Colson says the electrical service grounding system for a residence may have up to 25 ohms of resistance and still meet codes in some jurisdictions.
Different soil types display different levels of resistance, Colson points out. Loam and gumbo have low resistance, while clay and sandy clay have higher resistance. Sand gravel and rocky soils will have much higher resistance, and my not his the 10-ohm target.
The simplest grounding setup consists of a 8-foot copper-coated steel rod driven straight down into the ground. This is commonly used in residential systems, but may not provide the low resistance needed. Nor can installers count on using the plumbing system for a ground - modern systems use plastic lines, and plastic is a great electrical insulator. even the water in those pipes isn't a reliable ground - an air pocket may disrupt continuity, and in cold weather many systems are blown out to remove water and prevent freeze damage.
The moisture factor
For a reliable ground, the experts seek underground moisture-the wetter, the better.
In some cases, a second 8-foot grounding rod can be attached to the first, using a specialized "Cadweld" system that assures electrical conductivity and corrosion resistance. The double-length rod is then driven as far as it will go into the soil , and with luck, it will hit soil and moisture conditions needed for a low-resistance grounding system.
But depth of penetration is no guarantee of success. A rock ledge may be encountered, or there may be a pocket of sand underground. The water table may be too low to keep the soil moist enough to conduct electricity well enough.
In such cases, one technique sometimes used is to dig a pit or trench, put in a copper plate or sheet, and surround it with low-resistance soil or clay that can dissipate the current. The depth of the pit will be dependent on surrounding soil conditions.
Such grounding pits may need to have a drip irrigation system installed to assure adequate moisture. some need to have a pipe run into them that can be used to add ion-rich salt solutions that increase soil conductivity.
Once it's connected to moist, low-resistance soil, the grounding system must still be checked regularly. Chemical activity above and below ground can cause high-resistance corrision, not unlike the gunk that builds up on lead-acid battery terminals in vehicles.
"Good grounding is the backbone of any power protection system," says Joe Becker, owner of D&B Sales Associates, A Galena, Ill., company that specializes in coordinated solutions to protect all types of electrically powered equipment.
Becker says there are several symptoms that can indicate an electrical system is not properly grounded, including frequently blown fused, failure of components in computerized control systems and failure of modems and computers.
"All grounds should be tested with a proper resistance meter and all mechanical connections tightened annually, " Becker says. "While many of the new control systems have some level of protection built-in, it has been proved that damage stall occurs because the protection was inadequate or non-existent on certain critical elements of the overall system."
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