Fuses react very differently to transient surge current as opposed to sustained overload current conditions. Fuses and fusing concerns become complex when contained within surge suppression equipment. Utilizing current limiting fusing in any SPD can quickly become counterproductive because the device’s overall performance is hindered. These fuses greatly limit the total surge current capacity of a SPD to their own individual capacity. The causes of the hindrances are related to the various current ratings and the operational characteristics of specific types of fuses. While there are legitimate ways to compensate for this troublesome drawback, many suppressor manufacturers choose to misrepresent the facts and further complicate the issue.
Global Positioning System - GPS - has infiltrated modern life to such an extent that many people, systems and operations rely on its error-free functioning. GPS is used for navigation, synchronizing data on wireless networks and managing loads on vast power grids, making it an integral system within the transportation, telecommunication, manufacturing, electricity distribution, mining and construction industries, not to mention national defense.
The first consideration for GPS antenna placement is a clear view of the sky, preferably 360 degrees. In the usual installation, the GPS antenna is located low and close to the equipment building roof. If an outdoor cabinet, the antenna is mounted on the cabinet or very low on the adjacent monopole/tower. A direct lightning hit to the above mounted antenna is unlikely. Mounting on an equipment building roof or cabinet is the safest place since the potential rise on the outside of either of these structures would be more or less equal with the potential on the inside. The PolyPhaser protector is there to equalize the differential in potential that occurs between center conductor and shield of the coax cable on its way from the antenna to the receiver.
Before one can design a properly sized grounding system for the required fall of potential measurement, the resistivity of the soil must be known. The resistivity results will determine the conductor size, length, and number of radials required. The measurement will also determine how many rods are required, their length and their spacing on each radial.
The statement that rods should have a separation, “greater than the sum of their lengths apart,” originates from theory, and the fact almost all ground rods will saturate the soil to which they connect. A ground rod connects to localized, irregularly sized, three-dimensional electrical clumps. Depending on the soil make-up (layering, etc.), the volume of earth a ground rod can dump charge into can be generalized as the radius of a circle equal to the length of the rod at the circle’s center. This is known as the sphere of influence of the rod. The sum of the driven depths of two rods should be, theoretiin homogeneous soil, the closest that ground rods can be placed. Anything closer will cause the soil (clumps) connected in common to saturate even faster.
There are many opinions about how to ground equipment inside the equipment room. Two options are presented here. When a large conductor such as a tower has high peak current flow through it (such as a lightning strike), an intense magnetic field is created around the tower. This field radiates out orthogonally from the tower. Since the building or cabinet is usually close to the tower, equipment in the building is subject to intense moving magnetic fields.
Wood or fiberglass support structures are not a good idea. They are an insulator. The cabinet earth ground, coaxial cables, and conduits attached to the support would be the only conductive path for lightning energy. If a wood or fiberglass pole must be used, the first step is to provide an alternate conductive path down the pole to earth. A lightning diverter (lightning rod) on top of the pole (above the antenna) with a separate 3 inch copper strap as an earth ground conductor, would provide a low inductance/large surface area conductive path to an earth ground system.
One of the basic ideas in developing a protection strategy is not allowing stray energy to flow through the equipment. There are several ways to accomplish this. One is to totally disconnect the equipment! Another is to provide some form of impulse protector for each of the equipment’s Input or Output (I/O) ports. These ports are usually the ac power connection, a telephone, control, or data line, and an antenna transmission line. A protector on each of the l/O’s will protect that path from damage. However, it is also necessary to be careful about voltages that may exist between the I/O’s during a strike event.
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