Presentation on theme: "GROUND We walk on it, play on it, and live on it, but what is it in reality when it comes to communications systems, and how do we obtain a “TRUE” and."— Presentation transcript:
GROUND We walk on it, play on it, and live on it, but what is it in reality when it comes to communications systems, and how do we obtain a “TRUE” and SAFE ground?
Types Of Ground RF Ground DC Ground Lightning Ground Not necessarily the same as they have different characteristics!!
Ground Terminology Anode/Electrode Factors to determine in selecting electrodes include, ampacity (the ability to handle current or amps), corrosion resistance, life expectancy, resistance-to-temperature change, and of course resistance over time.. Bonding Making sure that all the electrical “devices” and/or circuits are tied together to form a common ground system or grid. THIS INCLUDES TOWERS!! Earthing The process of electrically connecting to the earth itself is often called “earthing”, particularly in Europe where the term “grounding” is used to describe the above ground wiring. The term “Grounding” is used in America to discuss both earthing and grounding.
Ground Factors Soil Resistivity Surface Area of Anode Zone or Sphere of Influence
ANODE/ELECTRODE An electrode is anything placed into the ground that is used to provide an electrical connection to the earth. The most common electrode is the copper-clad driven grounding rod. This grounding rod is essentially an 8 or 10-foot long shaft of mild-steel, thinly coated with copper and driven into the earth. The process of installing an electrode would be called “earthing”. Each electrode has its own unique advantages and disadvantages. In the case of the copper-clad driven rod, it is very inexpensive to purchase, but can be overly labor-intensive and time-consuming to install. It also has some poor electrical properties. On the other hand, electrolytic rods while cost prohibitive, out perform any other grounding electrode on the market today.
A common misconception is that the copper coating on a standard driven rod has been applied for electrical reasons. While copper is certainly a conductive material, its real purpose on the rod is to provide corrosion protection for the Steel underneath. Many corrosion problems can occur because copper is not always the best choice in corrosion protection. It should be noted that galvanized driven rods have been developed to address the corrosion concerns that copper presents, and in many cases are a better choice for prolonging the life of the grounding rod and grounding systems. Generally speaking, galvanized rods are a better choice in all but high salt environments.
Advanced Driven Rods can easily be installed to depths of 20 ft or more, depending upon soil conditions. Advanced Driven Rods are typically driven into the ground with a standard drill hammer. This automation dramatically reduces the time required for installation. The tip of an Advanced Driven Rod is typically made of carbide and works in a similar manner to a masonry drill bit, allowing the rod to bore through rock with relative ease. Advanced Driven Rods are modular in nature and are designed in five foot lengths.
Grounding plates should be buried at least 30 inches below grade level. While the surface area of grounding plates is greatly increased over that of a driven rod, the zone of influence is relatively small. The zone of influence of a grounding plate can be as small as 17 inches. This ultra-small zone of influence typically causes grounding plates to have a higher resistance reading than other electrodes of similar mass.
Concrete Encased Electrodes use a minimum No. 4 AWG copper wire at least 20 feet in length and encased in at least 2 inches of concrete. They dramatically increase the surface area and degree of contact with the surrounding soil. However, the zone of influence is not increased, therefore the resistance to ground is typically only slightly lower than the wire would be without the concrete.
Eliminates the drawbacks of other grounding electrodes. This active grounding electrode consists of a hollow copper shaft filled with natural earth salts and desiccants whose hygroscopic nature draws moisture from the air. The moisture mixes with the salts to form an electrolytic solution that continuously seeps into the surrounding backfill material, keeping it moist and high in ionic content.
Zone/Sphere Of Influence Determines how efficiently grounding electrodes discharge electrons into the earth. The “Sphere Of Influence” is the volume of soil throughout which the electrical potential from a lightning strike is dissipated. The greater the volume, the more efficient the electrode. The greater the surface area of the electrode, the greater the contact with the soil and the more electrical energy that can be discharged per unit of time.
A simpler version is used when the above formula is modified by rounding Π (pi) down to to 3 and cross canceling to get the formula: V=5L3 In this example, a single 10-foot driven rod would utilize 5,000 cubic feet of soil, where as a single 8 foot rod would utilize about half the soil at 2,560 cubic feet.
MEASUREMENTS Soil resistivity. Anode/Ground resistance Proper sized ground cable and anode In order to achieve reliable electrical grounding, it is absolutely essential that you verify:
Wenner 4-Point Soil Resistivity Test Uses 4 probes spaced at equal distances across the surface of the earth in a straight line The distance that the probes are spaced determines the testing depth into the soil Multiple tests are typically conducted at a variety of probe spacing
3 Point Method Fall Of Potential And Induced Frequency Ground Resistance Test Requires complete isolation from the power utility A short probe is driven into the earth at a distance of ten times the length of the grounding system. Often referred to as “Megger Test”.
Induced Frequency Test aka Clamp-On Testing Newest test method for measuring the ground resistance of a grounding system or electrode Induced Frequency test can be used on live or ‘hot” systems This ground resistance test is rapid and accurate
ADVANTAGES Measures Soil Resistivity Measures Electrode/Soil Contact Measures Ground System Current Measures Ground System Noise
Summary How good is YOUR ground? Grounding systems change over time. Regular testing a must to insure reliability Lightning “Season” fast approaching!!