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<br />ARTICLE 250 - GROUNDING
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<br />70-127 70-128
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<br />NATIONAL ELECTRICAl.. CODE
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<br />(b) Metal Frame of the Building. The metal frame of the building, where
<br />effectively grounded. .1 , ,
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<br />(FPN): Effectively grounded meansintentional1y connected to earth through a
<br />ground connection or connections of sufllciently low ltupedance and having suffi-
<br />cient current-canying capacity to prevent the btilldup ofWltagea that may result in
<br />undue hazard to c:onnected equipment or to pell!lOllS. .
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<br />ee) ~ Electrode. An electrode encased by at least 2
<br />H. Grounding Electrode System inches (SO.8 nun) of concrete, located within and near the bottom 'Of a con-
<br />, crete foundation or footing that is in direct contact with the earth, consist-
<br />250-81. ,G~ndlng Electrode System., If available on the premises atl ing of at least 20 feet (6.f m) of one or more bare or zinc galvanized or
<br />each building or structure served, each Item (a) throuJdt (d) below, and any otherelectricaIJy conductive coated steel reinforcing bars or rods of not
<br />made electrodes in accordance with Sections 25O-83'(c) and (d), shall be. less than Ih inch (127 nun) diameter or consisting of at least 20 feet
<br />bonded together to form the grounding electrode system. Interior metall (6.1 m) of bare coppe; conductor nots:Oaller than No.4.
<br />water piping lOCated more than 5 feet (152 em) from the point of entrance , " , . ,
<br />to the building shall not be used as a conductor to interconnect the elec- ,(d) Ground RI.ng. A ground nng encircling the building or structure, m
<br />trodes and the grounding electrode conductor. The bonding jumper shall be direct contact With the ,elJ!th at a depth below earth surface not less than
<br />installed in accordance with Sections 250-92(a) and (b), shall be sized in 2V2 feet (762 nun), COnsISting of at least 20 feet (6.1 m) of bare copper con-
<br />accordance with Section 250-94, and shall be connected in the mannerl ductor not smaller than No.2.
<br />specified in Section 250-115. The unspliced grounding electrode conductor
<br />shall be permitted to run to any convenient grounding electrode available ~~. M~ and. ~ ~ . Where none of the electrodes sp-cc-
<br />in the grounding electrode system. It shall be sized for the largest ground- !fled m Section 250-81 IS available, one or more of !he electrodes specified
<br />ing electrode conductor required among all the available electrodes m (b) throuJdt (d) below shall be used. Where practicable, made electrodes
<br />. . . . .' shall be embedded below permanent moisture level. Made electrodes shall
<br />Exceptton No.1: It s'!aU be J!i!'"l#ted to sI?lice the growtding e~ctrode be free fJ;om nonconductive coatings, such as paint or enamel. Where more
<br />conductor by means of I17'f!Vt;rsible c:ompresslOn-type connectors listed for than one electrode is used, each electrode of one grounding system (includ-
<br />the purpose or the exothennic welding process. ing that used for lightning rods) shall not be less than 6 feet (1.83 m) from
<br />Exception No.2: In industrial and commercial buildings where condi. any other electrode of another grounding system. .
<br />tions of maintenance and supervision ensure that only qualified persons . ,
<br />will service the installation and the entire length of the interior metal water (FPN): ~ or more electrodes, that, are effectively bonded together are to be
<br />pipe that is being used for the conductor is expos(!d. treated as a smgle electrode Iystem m this sense. ," .
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<br />(FPN): See Section 547-8 for special grounding and bonding requirements for "(~) ",etaI Underground Gee PlplngS~ A metal underground gas
<br />agncultural buildings. plpmg system shall not be used as a grounding electrode.
<br />,. (b) Other Local Metal Underground SptemI or Structu..... Other local
<br />,(a) Metal Und~ground Water Pipe. A metal underground ,water,plpe In metal underground systems or structures such' as piping systems and
<br />direct contact With the earth for 10 feet (3.05 m) or more (mcludiDg any underground tanks '. ,
<br />metal well casing effectively bonded to the pipe) and electrically continu- . ,
<br />ous (or made electrically continuous by bonding around insulating joints or (e) Rod and Pipe ~ectrodeL Rod and plJ?C electrodes sh~ not be ,less
<br />sections or insulating pipe).to the pomts of connection of the grounding than 8 feet (~.44 m) I~ length and ,shall conSISt of the foUowmg matenals,
<br />electrode condu(;tor and the bonding conductors. Continuity of the ground- and shall be mstalled m the foUowmg manner:
<br />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 ~4-inch trade
<br />meters. A metal underground water I?ipe shall be supplemented by an size and, whereof iron or steel, shall have the outer surface galvanized or
<br />additional electrode of a type specified In Section 250-81 or in Section 250- otherwise metal-coated for corrosion protection.
<br />83. The supplemental electrode shall ~ permitted to be bonded to the f2) Electrodes of rods ofiron or steel shall be at least %'8 inch (15.87 mm)
<br />grounding electnx!e conductor, the groUnded servi~-entrance conductor'I' in diameter. Stainless steel rods less than %'8 inch (15.87 mm)in diameter,
<br />the grounded seIVIce raceway, or any grounQed seIVIce enclosure. I nonferrous rods or their equivalent shall be Iisted and shall not be less than
<br />W~re the supple~ental electrode ,is a. made electf!XIe as in Section 2;)0- V2 inch (12.7 om't) in diameter. ",
<br />83(c) or (d), that portion of !he bondmg Jumper that IS the ,sole connection (3) The electrode shall be installed such"that at least 8 feet (2.44 m) of
<br />to the supplemental $founding electr~e shall. not be requaed to be larger length is in contact with the soil. It shall be driven to a depth of not less
<br />than No.6 copper wae or No.4 alununum wae. 'than 8 feet (2.44 m) except that, where rock bottom is encountered, the
<br />Exceftion: The supplemental electrode shaU be permitted to be bonded I electrode shall be driven at an oblique angle not to exceed 45 degrees from
<br />to the Interior metal water piping at a'9' convenient point as covered in the vertical or shall be buried in a trench that is at least 2V2 feet (762 mm)
<br />Section 250-81, Exception No.2.:' deep. The upper end of the electrode shall be flush with or below ground
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<br />jumper shall be sized in aCC()rdance with Table 25~95 using the rating of
<br />the circuit that may enersize the piping. .
<br />The equipment grounding conductor for the circuit that may energize the
<br />piping shall be permitted to serve as the bondipg means.
<br />(FPN): Bonding all piping and metal air ducts within the premises will provide
<br />additional safety. ,
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