Many people have heard of the term “grounding”, but few fully understand its meaning and importance. Sometimes, even experienced electricians do not treat grounding as a serious issue. The impact of an incorrect or absent grounding ranges from noise interference, resonance or humming during the use of electrical equipment to the worst case where electricity leakage through the chassis causes personal injury or damage to instrument components. Grounding, therefore, is a very practical issue that should be dealt with properly. For those who operate electrical equipment frequently, a complete understanding of grounding theories and applications is necessary in order to become a best-in-class technician.
Grounding the Electrical System Reference: AAVIM “Electrical Wiring” Created May 2007 Purpose of the Grounding System • Fundamental to the safety of those installing, using, and servicing the electrical system • Assures the system will work properly while preventing damage to the system NEC Requirements • All electrical systems serving structure must be bonded together • Including the following – Electrical wiring system – Telephone system – Phone system – Burgular alarm system – Cable or satellite system Grounding • The process of making a planned, continuous, connection between NON- CURRENT CARRYING parts of the electrical wiring installation and the earth and some other conducting body Grounded • Describes the act of being connected to the earth or some other conduction body that serves in place of the earth Bonding • Process in which all NON-CURRENT CARRYING METALLIC parts of the electrical wiring system are permanently joined together to form a CONTINUOUS grounding path Bonding • Reduces the differences in potential between each electrical system • May be caused by power surges, lightning strikes or other types of ground fault type occurences Parts of the Electrical System • Circuits • Service Entrance Panel • Metal Water Pipe • Metal Gas pipe Materials in Grounding System • Must be approved by NEC The Grounding Electrode System • All materials must be grounded using approved bonding and grounding electrode systems • Check with local building code Metallic Pipe • Water pipe must always be bonded to the service entrance panel, grounding electrode conductor, or grounding electrode • Other metal pipe, such as gas pipe, which may become energized accidentally must be bonded to the electrical system grounded system Use of Bonding Jumper • To provide CONTINUOUS grounding path around devices such as water meters installed in metallic water pipe system Types of Grounding Electrodes Metal Underground Water Pipe • Must be bonded to the supplemental grounding system electrode and to the neutral bus bar in the SEP • Connection must be made within 5 feet of entering structure • Water pipe must be in direct contact with the earth for at least 10 feet Concrete Encased Electrode • Electrode encased in foundation footing covered with at least 2 inches of concrete • Electrodes must be at least 20 feet in length and consist of one or more ½” steel reinforcement bars Ground Ring • Bare Copper • At Least #2 AWG or larger • Encircling residence for a length of 20 feet • Buried at least 2 ½” Metal Framework Supplemental Electrodes • Typically made of metal rods, pipes, or plates Rod and Pipe Electrodes • Iron or steel rod electrodes • Must be 5/8” in diameter • Pipe must be ¾” in diameter • Galvanized or metal coated for corrosion resistance • 8 feet in length • Installed to a depth of 8” in direct contact with earth • Nonferrous rods must be listed at no less than ½” • Stainless Steel- ½” diamter • Must be at or below ground level • Must be protected from physical damage Exceptions • If electrode can not be driven more than 4” into the earth b/c of rock or other obstruction • May be driven at an oblique and of no more than 45° from vertical • At least 8” of the electrode must be in contact with earth Multiple grounding rods • When more than one electrode grounding rod is used: – Must be installed not less than 6 feet apart – Must be bonded together with an approved bonding jumper to form single grounding electrode system Plate Electrode • May be used in areas where it is not possible to use a grounding rod or ring • Steel/Iron Plate electrode must be ¼” thick • Non-ferrous metal plate must be 0.06” thick • 2 feet square • Buried at least 2 1/2’ Grounding Electrode Conductor • NEC permits – Copper – Aluminium – Copper-clad AL and AL-CU may not be used in contact with masonry, corrosive, or in direct contact with the earth
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