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� , , .- . ARTICLE 250—GROUNDING 70-1'27 7��1 Z8 NATIONAL.ELECTRICAL CODE ' � jumper shall be sized in accordance with Table 250=95 using the rating of (b) Metal Frame of the Bullding. The metal frame of the building,where the circuit that may ener�ize�the piping. effectively grounded. �` The equipment groundmg conductor for the circuit that may energize the �FpI�: Effectively grounded means intentionally wnnected to earth through a piping shall be permitted to serve as the bonding means. ground connection or connections of sufficientty low impedance and having sug'i- (FPI�: Bonding all piping and metal air ducts within the premises will provide cient current-carrying capacity to•prevent the buildup of voltages that may result in additional safety. , undue hazard to connected eqwpment or to persons. (c) Concrete-Encased ElecVode..An electrode encased by at least 2 H:Grourniing Electrode System inches(50.8 mm)of concrete,.located within and near the bottom�of a con- crete foundation or footing that is in d'uect contact with the earth,consist- 250-Si. Grounding Electrode System. If available on the premises at �g of at least 20 feet (6.1 m) of one or more baze or zinc gatvanized or each building or structure seived,each item(a)through(d)below,and anyl other electrically conductive coated steel reinforcing bars or rods of not made electrodes in accordance with Sections 250-83(c) and (d), shall be less than �/2 inch (12.7 mm) diameter, or consisting of at least 20 feet bonded together to form the grounding electrode system. Interior metal� (6.1 m)of bare copper conductor not smaller than No.4. water piping located more than 5 feet(152 cm)from the point of entrance to the building shall not be used as a conductor to interconnect the elec- (d) Ground R(ng. A ground ring encircling the building or structure, in trodes and the grounding electrode conductor.The bonding jumper shall be direct contact with the earth at a depth below earth surface not less than installed in accordance with Sections 250-92(a) and (b), shall be sized in 2�/2 feet(762.mm),consisting of at least 20 feet(6.1 m)of.bare wpper con- accordance with Section 250-94, and shall be connected in the manner� ductor not smaller than No.2. specified in Section 250-115.The unspliced grounding electrode conductor shall be pernutted to run to any convenient grounding electrode available 250-83. Made and.Other Electrodes. Where none of the electrodes s�ec- in the grounding electrode system. It shall be sized for the largest ground- �ed in Section 250-81 is available,one or more of the electrades specified ing electrode wnductor required among all the available electrodes. in(b)throu�(d)below shall be used.Where practicable,�tade electrodes Fxception No. 1: It shall be permitted to splice the grounding e[ectrode shall be em edded below pertnanent moisture level.Made electrodes shall conductor by means of irreversible compression-type connectors listed for be free from nonwnductive coatings,such as paint or enamel.Where more the u ose or the e.xothermic weldin rocess. than one electrode is used,each electrode of one grounding system(includ- P �P gP ing that used for lightning rods)shall not be less than 6 feet(1.83 m)from Exception No. 2: In industrial and commercial buildings where condi- any other electrode of another grounding system. ' tions of mairttenance and supervision ensure that only qualifted persons ��: �,o or more electrodes that aze effectively bonded together are to be will service the installation and the entire length of the interior metal water treated as a singie electrode'system in this sense. pipe that is being used for the conductor is exposed. (FPN): See Section 547-8 for special grounding and bonding requirements.for � (a) Metal Underground Gas Plping System. A metal underground gas agncultural buildings. piping system shall not be used as a grounding electrode. a Metal vnder round Water Pi e A metal under ound water i e in �b) Other Local Metai Underground Systems or Structures. Other local ( ) 9 P • �' P P metal underground systems or structures, such�as,piping systems and direct contact with the earth for 10 feet (3.05 m) or more (including any underground Eanks. metal well casing effectively bonded to the pipe) and electncally continu- c Rod and Pi e Electrodes. Rod and i e electrodes shall not be less ous(or made electrically continuous by bond'mg around insulating�oints or � � p P P sections or insulating pipe).to the points of connection of the grounding than 8 feet(2.44 m)in length and shall cons�st of the following materials, electrode conductor and the bonding conductors.Continuity of the ground- �d shall be installed in the following manner: ing path or the bonding connection to interior piping shall not rely on water (1) Electrodes of pipe or conduit shall not be smaller than 3/a-inch trade �i meters. A metal underground water pipe shall be supplemented by an size and,where of iron or steel,shall have the outer surface galvanized or additional electrode of a type specified in Section 250-81 or in Section 250- otherwise metal-coated for conosion protection. 83. The supplemental electrode shall b� pemutted to be bonded to the (2) Electrodes of rods of iron or steel shall be at least 5/8 inch(15.87 mm) grounding electrode conductor, the grounded service-entrance conductor,I_� diameter. Stainless steel rods less than 5/$ inch (15.87 mm) in diameter, the grounded service raceway,or any grounaed service enclosure. �nonferrous rods,or their equivalent shall be listed and shall not be less than Wl�ere the supplemental electrode is a made electrode as in Section 250- �/Z�ch(12.7 mm)in diameter. ' 83(c)or(d), that portion of the bonding jumper that is the sole connection �3) The electrode shall be installed such�that at least 8 feet(2.44 m)of to the supplemental prounding electrode shall not be required to be larger length is in contact with the soil. It shall be driven to a depth of not less than No. 6 copper wue or No.4 aluminum wire. than 8 feet (2.44 m) except that,where rock bottom is encountered, the Fxception: Tlae supplemental electrode shall be permitted to be bonded electrode shall be driven at an oblique angle not to exceed 45 degrees from to the interior metal water piping at arry convenient point as covered in I the vertical or shall be buried in a trench that is at least 2�/Z feet(762 mm) Section 250-81, Fxception No. 2. deep.The upper end of the electrode shall be$ush with or below ground