![]() The zone of influence of a grounding plate can be as small as 17 inches. While the surface area of grounding plates is greatly increased over that of a driven rod, the zone of influence is relatively small as shown in “B”. Grounding plates should be buried at least 30 inches below grade level. Grounding plates are typically placed under poles or supplementing buried ground rings. ![]() Ferrous materials must be at least 0.20 inches thick, while non-ferrous materials (copper) need only be 0.060 inches thick. The National Electrical Code requires that ground plates have at least 2 ft 2 of surface area exposed to the surrounding soil. “Real knowledge is to know the extent of one's ignorance.Grounding plates are typically thin copper plates buried in direct contact with the earth. For the protection to work properly they must installed correctly and be fast enough to eliminate or minimize damage. This goes hand in hand with overcurrent protection. The grounding system is for protection of people, equipment and fire. So having a low impedance path to ground is crucial. When electrical path in the grounding circuit is greater than a person in contact with an energized material it can and will travel through that person. So when impedance increases even slightly, the electrical current seeks other paths to ground. Electricity will follow “all paths” back to the source, but it will follow paths proportionally according to the conductivity of each path. The notion about electricity following the path of least resistance is actually incorrect. Now for a little more about electricity and how it travels. At the end of the study in 1960, the average of 24 installations was 3.57 ohms, none ever exceeding 4.8 ohms over the 18 years. Ufer performed an 18 year study on the resistance of concrete-encased electrodes. It has been shown that the “UFER” ground achieves 5 ohms or less. But here is the catch once a second rod is installed they do not need to confirm that it has a resistance of less than 25 ohms.Įnter the CEE or UFER ground. For residential ground rod the NEC requires 25 ohms or it must be supplemented with another rod. For utilities they are looking for grounding system that are 1 ohm or less and most commercial facilities are looking for 5 ohms or less. The lower the impedance, the easier it is for electricity to flow through an object. The degree of resistance is measured in units known as ohms. Impedance, in very simple terms, is resistance occurring in AC electrical circuits. This brings us to impedance and its effect on the grounding system. But really it is connecting the circuit to a common point of reference which in most cases is the earth. The term for most purposes means earthing or connecting the circuit to the earth. The main reason for grounding in electrical systems is safety. Grounding (and bonding) is maybe the most overlooked and misunderstood part of the electrical systems. Herbert Ufer realized that this means that concrete had a ready supply of ions and so provides a better electrical grounding path in almost any type of soil. Concrete also absorbs moisture very quickly and releases moisture very slowly. The “UFER” technique uses the construction of concrete foundations to create a low impedance alternative for grounding.Ĭoncrete has a high pH (known as a base chemically). Most grounding systems rely on moisture and pH in the soil and to create a low impedance path to the earth. This is a grounding method that was developed during WWII to provide an electrical earth grounding method in dry areas. I was asked to write a little background on Concrete Encased Electrodes (CEE) or what is referred to as a “UFER Ground”.
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