The structural metal frame of a building shall not be used

as the required equipment grounding conductor for ac equipment. ARTICLE 250 - GROUNDING 70-121 (b) Metal Car Frames. Metal car frames supported by metal hoisting cables attached to or running over metal sheaves or drums of elevator machines that are grounded by one of the methods indicated in Section 250-57. 250-59. Cord- and Plug-Connected Equipment. Noncurrent-carrying metal parts of cord- and plug-connected equipment, where required to be grounded, shall be grounded by one of the methods indicated in (a), (b), or (c) below. (a) By Means of the Metal Enclosure. By means of the metal enclosure of the conductors supplying such equipment if a grounding-type attachment plug with one fixed grounding contact is used for grounding the metal enclosure, and if the metal enclosure of the conductors is secured to the attachment plug and to equipment by approved connectors. Exception: A self-restoring grounding contact shall be permitted on grounding-type attachment plugs used on the power supply cord of portable hand-held, hand-guided, or hand-supported tools or appliances. (b) By Means of a Grounding Conductor. By means of an equipment grounding conductor run with the power supply conductors in a cable assembly or flexible cord properly terminated in grounding-type attachment plug with one fixed grounding contact. An uninsulated equipment grounding conductor shall be permitted, but, if individually covered, the covering shall have a continuous outer finish that is either green or green with one or more yellow stripes. Exception: A self-restoring grounding contact shall be permitted on grounding-type attachment plugs used on the power supply cord of portable hand-held, hand-guided, or hand-supported tools or appliances. (c) Separate Flexible Wire or Strap. By means of a separate flexible wire or strap, insulated or bare, protected as well as practicable against physical damage, where part of equipment. 250-60. Frames of Ranges and Clothes Dryers. Frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be grounded in the manner specified by Section 250-57 or 250- 59; or, except for mobile homes and recreational vehicles, shall be permitted to be grounded to the grounded circuit conductor if all of the conditions indicated in (a) through (d) below are met. (a) The supply circuit is 120/240-volt, single-phase, 3-wire; or 208Y/120- volt derived from a 3-phase, 4-wire wye-connected system. (b) The grounded conductor is not smaller.than No. 10 copper or No. 8 aluminum. (c) The grounded conductor is insulated; or the grounded conductor is uninsulated and part of a Type SE service-entrance cable and the branch circuit originates at the service equipment. 70-122 NATIONAL ELECTRICAL CODE (d) Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment. 250-61. Use of Grounded Circuit Conductor for Grounding Equipment. (a) Supply-Side Equipment. A grounded circuit conductor shall be permitted to ground noncurrent-carrying metal parts of equipment, raceways, and other enclosures at any of the following locations: (1) On the supply side of the service disconnecting means. (2) On the supply side of the main disconnecting means for separate buildings as provided in Section 250-24. (3) On the supply side of the disconnecting means or overcurrent devices of a separately derived system. (b) Load-Side Equipment. A grounded circuit conductor shall not be used for grounding noncurrent-carrying metal parts of equipment on the load side of the service disconnecting means or on the load side of a separately derived system disconnecting means or the overcurrent devices for a separately derived system not having a main disconnecting means. Exception No. 1: The frames of ranges, wall-mounted ovens, countermounted cooking units, and clothes dryers under the conditions specified by Section 250-60. Exception No. 2: As permitted in Section 250-24 for separate buildings. Exception No. 3: It shall be permissible to ground meter enclosures by connection to the grounded circuit conductor on the load-side of the service disconnect if: a. No service ground-fault protection is installed; and b. All meter enclosures are located near the service disconnecting means. Exception No. 4: As required in Sections 710-72(e)(1) and 710-74. Exception No. 5: DC systems shall be permitted to be grounded on the load side of the disconnecting means or overcurrent device in accordance with Section 250-22, Exception. 250-62. Multiple Circuit Connections. Where equipment is required to be grounded, and is supplied by separate connection to more than one circuit or grounded premises wiring system, a means for grounding shall be provided for each such connection as specified in Sections 250-57 and 250-59. G. Bonding 250-70. General. Bonding shall be provided where necessary to assure electrical continuity and the capacity to conduct safely any fault current likely to be imposed. 250-71. Service Equipment. (a) Bonding of Service Equipment. The noncurrent-carrying metal parts of equipment indicated in (1), (2), and (3) below shall be effectively bonded together. ARTICLE 250 - GROUNDING 70-123 (1) Except as permitted in Section 250-55, the service raceways, cable trays, cablebus framework, or service cable armor or sheath. (2) All service equipment enclosures containing service conductors, including meter fittings, boxes, or the like, interposed in the service raceway or armor. (3) Any metallic raceway or armor enclosing a grounding electrode conductor as permitted in Section 250-92(a). Bonding shall apply at each end and to all intervening raceways, boxes, and enclosures between the service equipment and the grounding electrode. (b) Bonding to Other Systems. An accessible means external to enclosures for connecting intersystem bonding and grounding conductors shall be provided at the service by at least one of the following means: (1) Exposed metallic service raceways. (2) Exposed grounding electrode conductor. (3) Approved means for the external connection of a copper or other corrosion-resistant bonding or grounding conductor to the service raceway or equipment. For the purposes of providing an accessible means for intersystem bonding, the disconnecting means at a separate building or structure as permitted in Section 250-24 and the disconnecting means at a mobile home as permitted in Section 550-23(a), Exception No. 1 shall be considered the service equipment. (FPN No. 1): A No. 6 copper conductor with one end bonded to the service raceway or equipment and with 6 inches (152 mm) or more of the other end made accessible on the outside wall is an example of the approved means covered in (b)(3). (FPN No. 2): See Sections 800-40 and 820-40 for bonding and grounding requirements for communications and CATV circuits. 250-72. Method of Bonding Service Equipment. Electrical continuity at service equipment shall be assured by one of the methods specified in (a) through (e) below. (a) Grounded Service Conductor. Bonding equipment to the grounded service conductor in a manner provided in Section 250-113. (b) Threaded Connections. Connections utilizing threaded couplings or threaded bosses on enclosures shall be made up wrenchtight where rigid metal conduit or intermediate metal conduit is involved. (c) Threadless Couplings and Connectors. Threadless couplings and connectors made up tight for rigid metal conduit, intermediate metal conduit and electrical metallic tubing. Standard locknuts or bushings shall not be used for the bonding required by this section. (d) Bonding Jumpers. Bonding. jumpers meeting the other requirements of this article shall be used around concentric or eccentric knockouts that are punched or otherwise formed so as to impair the electrical connection to ground. (e) Other Devices. Other approved devices, such as bonding-type locknuts and bushings. 70-124 NATIONAL ELECTRICAL CODE 250-73. Metal Armor or Tape of Service Cable. The metal covering of service cable having an uninsulated grounded service conductor in continuous electrical contact with its metallic armor or tape shall be considered to be grounded. 250-74. Connecting Receptacle Grounding Terminal to Box. An equipment bonding jumper shall be used to connect the grounding terminal of a grounding-type receptacle to a grounded box. Exception No. 1: Where the box is surface mounted, direct metal-tometal contact between the device yoke and the box shall be permitted to ground the receptacle to the box. This exception shall not apply to covermounted receptacles unless the box and cover combination are listed as providing satisfactory ground continuity between the box and the receptacle. Exception No. 2: Contact devices or yokes designed and listed for the purpose shall be permitted in conjunction with the supporting screws to establish the grounding circuit between the device yoke and flush-type boxes. Exception No. 3: Floor boxes designed for and listed as providing satisfactory ground continuity between the box and the device. Exception No. 4: Where required for the reduction of electrical noise (electromagnetic interference) on the grounding circuit, a receptacle in which the grounding terminal is purposely insulated from the receptacle mounting means shall be permitted. The receptacle grounding terminal shall be grounded by an insulated equipment grounding conductor run with the circuit conductors. This grounding conductor shall be permitted to pass through one or more panelboards without connection to the panelboard grounding terminal as permitted in Section 384-20, Exception so as to terminate within the same building or structure directly at an equipment grounding conductor terminal of the applicable derived system or service. (FPN): Use of an isolated equipment grounding conductor does not relieve the requirement for grounding the raceway system and outlet box. 250-75. Bonding Other Enclosures. Metal raceways, cable trays, cable armor, cable sheath, enclosures, frames, fittings, and other metal noncurrent-carrying parts that are to serve as grounding conductors with or without the use of supplementary equipment grounding conductors shall be effectively bonded where necessary to assure electrical continuity and the capacity to conduct safely any fault current likely to be imposed on them. Any nonconductive paint, enamel, or similar coating shall be removed at threads, contact points, and contact surfaces or be connected by means of fittings so designed as to make such removal unnecessary. Exception: Where required for the reduction of electrical noise (electromagnetic interference) on the grounding circuit, an equipment enclosure supplied by a branch circuit shall be permitted to be isolated from a raceway containing circuits supplying only that equipment by one or more listed nonmetallic raceway fittings located at the point of attachment of the raceway to the equipment enclosure. The metal raceway shall comply with provisions of this article and shall be supplemented by an internal insu- ARTICLE 250 - GROUNDING 70-125 lated equipment grounding conductor installed in accordance with Section 250-74, Exception No. 4 to ground the equipment enclosure. (FPN): Use of an isolated equipment grounding conductor does not relieve the requirement for grounding the raceway system. 250-76. Bonding for Over 250 Volts. For circuits of over 250 volts to ground, the electrical continuity of metal raceways and cables with metal sheaths that contain any conductor other than service conductors shall be assured by one or more of the methods specified for services in Sections 250-72(b) through (e). Exception: Where oversized, concentric, or eccentric knockouts are not encountered, the following methods shall be permitted: a. Threadless couplings and connectors for cables with metal sheaths. b. Two locknuts, on rigid metal conduit, or intermediate metal conduit, one inside and one outside of boxes and cabinets. c. Fittings with shoulders that seat firmly against the box or cabinet, such as electrical metallic tubing connectors, flexible metal conduit connectors, and cable connectors, with one locknut on the inside of boxes and cabinets. 250-77. Bonding Loosely Jointed Metal Raceways. Expansion joints and telescoping sections of raceways shall be made electrically continuous by equipment bonding jumpers or other means. 250-78. Bonding in Hazardous (Classified) Locations. Regardless of the voltage of the electrical system, the electrical continuity of noncurrentcarrying metal parts of equipment, raceways, and other enclosures in any hazardous (classified) location as defined in Article 500 shall be assured by any of the methods specified for services in Sections 250-72(b) through (e) that are approved for the wiring method used. 250-79. Main and Equipment Bonding Jumpers. (a) Material. Main and equipment bonding jumpers shall be of copper or other corrosion-resistant material. A main bonding jumper shall be a wire, bus, screw, or similar suitable conductor. (b) Construction. Where a main bonding jumper is a screw only, the I screw shall be identified with a green finish that shall be visible with the screw installed. (c) Attachment. Main and equipment bonding jumpers shall be attached in the manner specified by the applicable provisions of Section 250-113 for circuits and equipment and by Section 250-115 for grounding electrodes. (d) Size - Equipment Bonding Jumper on Supply Side of Service and Main Bonding Jumper. The bonding jumper shall not be smaller than the sizes shown in Table 250-94 for grounding electrode conductors. Where the service-entrance phase conductors are larger than 1100 kcmil copper or 1750 kcmil aluminum, the bonding jumper shall have an area not less than 12½ percent of the area of the largest phase conductor except that, where the phase conductors and the bonding jumper are of different materials 70-126 NATIONAL ELECTRICAL CODE (copper or aluminum), the minimum size of the bonding jumper shall be based on the assumed use of phase conductors of the same material as the bonding jumper and with an ampacity equivalent to that of the installed phase conductors. Where the service-entrance conductors are paralleled in two or more raceways or cables, the equipment bonding jumper, where routed with the raceways or cables, shall be run in parallel. The size of the bonding jumper for each raceway or cable shall be based on the size of the service-entrance conductors in each raceway or cable. The bonding jumper for a grounding electrode conductor raceway or cable armor as covered in Section 250-92(b) shall be the same size or larger than the required enclosed grounding electrode conductor. (e) Size - Equipment Bonding Jumper on Load Side of Service. The equipment bonding jumper on the load side of the service overcurrent devices shall not be smaller than the sizes listed in Table 250-95. A single common continuous equipment bonding jumper shall be permitted to bond two or more raceways or cables where the bonding jumper is sized in accordance with Table 250-95 for the largest overcurrent device supplying circuits therein. Exception: The equipment bonding jumper shall not be required to be larger than the circuit conductors supplying the equipment, but shall not be smaller than No. 14. (f) Installation - Equipment Bonding Jumper. The equipment bonding jumper shall be permitted to be installed inside or outside of a raceway or enclosure. Where installed on the outside, the length of the equipment bonding jumper shall not exceed 6 feet (1.83 m) and shall be routed with the raceway or enclosure. Where installed inside of a raceway, the equipment bonding jumper shall comply with the requirements of Sections 250- 114 and 310-12(b). 250-80. Bonding of Piping Systems. (a) Metal Water Piping. The interior metal water piping system shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or to the one or more grounding electrodes used. The bonding jumper shall be sized in accordance with Table 250-94 and installed in accordance with Sections 250-92(a) and (b). The points of attachment of the bonding jumper shall be accessible. Exception: In buildings of multiple occupancy, where the interior metal water piping system for the individual occupancies is metallically isolated from all other occupancies by use of nonmetallic water piping, the interior metal water piping system for each occupancy shall be permitted to be bonded to the panelboard or switchboard enclosure (other than service equipment) supplying that occupancy. The bonding jumper shall be sized in accordance with Table 250-95. (b) Other Metal Piping. Interior metal piping that may become energized shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or to the one or more grounding electrodes used. The bonding ARTICLE 250 - GROUNDING 70-127 jumper shall be sized in accordance with Table 250-95 using the rating of the circuit that may energize the piping. The equipment grounding conductor for the circuit that may energize the piping shall be permitted to serve as the bonding means. (FPN): Bonding all piping and metal air ducts within the premises will provide additional safety. H. Grounding Electrode System 250-81. Grounding Electrode System. If available on the premises at each building or structure served, each item (a) through (d) below, and any made electrodes in accordance with Sections 250-83(c) and (d), shall be bonded together to form the grounding electrode system. Interior metal 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 electrodes and the grounding electrode conductor. The bonding jumper shall be installed in accordance with Sections 250-92(a) and (b), shall be sized in accordance with Section 250-94, and shall be connected in the manner specified in Section 250-115. The unspliced grounding electrode conductor shall be permitted to run to any convenient grounding electrode available in the grounding electrode system. It shall be sized for the largest grounding electrode conductor required among all the available electrodes. Exception No. 1: It shall be permitted to splice the grounding electrode conductor by means of irreversible compression-type connectors listed for the purpose or the exothermic welding process. Exception No. 2: In industrial and commercial buildings where conditions of maintenance and supervision ensure that only qualified persons will service the installation and the entire length of the interior metal water pipe that is being used for the conductor is exposed. (FPN): See Section 547-8 for special grounding and bonding requirements for agricultural buildings. (a) Metal Underground Water Pipe. A metal underground water pipe in direct contact with the earth for 10 feet (3.05 m) or more (including any metal well casing effectively bonded to the pipe) and electrically continuous (or made electrically continuous by bonding around insulating joints or sections or insulating pipe) to the points of connection of the grounding electrode conductor and the bonding conductors. Continuity of the grounding path or the bonding connection to interior piping shall not rely on water meters. A metal underground water pipe shall be supplemented by an additional electrode of a type specified in Section 250-81 or in Section 250- 83. The supplemental electrode shall be permitted to be bonded to the grounding electrode conductor, the grounded service-entrance conductor, the grounded service raceway, or any grounded service enclosure. Where the supplemental electrode is a made electrode as in Section 250- 83(c) or (d), that portion of the bonding jumper that is the sole connection to the supplemental grounding electrode shall not be required to be larger than No. 6 copper wire or No. 4 aluminum wire. Exception: The supplemental electrode shall be permitted to be bonded to the interior metal water piping at any convenient point as covered in