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r enclosures, if grounded, shall be connected to an equipment grounding conductor by one of the following methods: * (1) By connecting to any of the equipment grounding conductors permitted by 250.118(2) through (14) * (2) By connecting to an equipment grounding conductor of the wire type that is co...

r enclosures, if grounded, shall be connected to an equipment grounding conductor by one of the following methods: * (1) By connecting to any of the equipment grounding conductors permitted by 250.118(2) through (14) * (2) By connecting to an equipment grounding conductor of the wire type that is contained within the same raceway, contained within the same cable, or otherwise run with the circuit conductors Exception No. 1: As provided in 250.130(C), the equipment grounding conductor shall be permitted to be run separately from the circuit conductors. Exception No. 2: For dc circuits, the equipment grounding conductor shall be permitted to be run separately from the circuit conductors Informational Note No. 1: See 250.102 and 250.168 for equipment bonding jumper requirements. Informational Note No. 2: See 400.10 for use of flexible cords and flexible cables for fixed equipment. ENHANCED CONTENT Collapse The EGC run in the same raceway or cable as the circuit conductor(s) allows the magnetic field developed by the circuit conductor and the EGC to cancel, reducing their impedance. Magnetic flux strength is inversely proportional to the square of the distance between the two conductors. By placing an EGC away from the conductor delivering the fault current, the magnetic flux cancellation decreases. This increases the impedance of the fault path and delays operation of the protective device contrary to the performance requirements specified in 250.4(A)(5) and (B)(4) for the ground-fault current return path. 250.136 Equipment Secured to a Metal Rack or Structure. If a metal rack or structure is connected to an equipment grounding conductor in accordance with 250.134, it shall be permitted to serve as the equipment grounding conductor for electrical equipment secured to and in electrical contact with the metal rack or structure. ENHANCED CONTENT Collapse Equipment bolted or securely clamped to the rack will typically provide the necessary electrical contact to ensure a low impedance connection between the rack and the equipment. If the rack has been painted, 250.12 requires the paint to be removed to ensure good electrical continuity. An example of electrical equipment secured to and in electrical contact with a metal rack is shown below. It is effectively grounded by the equipment bonding jumper installed between the safety switch and the rack. Building steel is not permitted as the equipment grounding conductor by 250.134 and 300.3(B). 250.138 Cord-and-Plug-Connected Equipment. Non-current-carrying metal parts of cord-and-plug-connected equipment, if required to be connected to an equipment grounding conductor, shall be connected by one of the methods in 250.138(A) or (B). (A) By Means of an Equipment 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 a grounding-type attachment plug with one fixed grounding contact. Exception: The grounding contacting pole of grounding-type plug-in ground-fault circuit interrupters shall be permitted to be of the movable, self-restoring type on circuits operating at not over 150 volts between any two conductors or over 150 volts between any conductor and ground. (B) By Means of a Separate Flexible Wire or Strap. By means of a separate flexible wire or strap, insulated or bare, connected to an equipment grounding conductor, and protected as well as practicable against physical damage, if part of equipment. 250.140 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 shall be connected to the equipment grounding conductor in accordance with 250.140(A) or the grounded conductor in accordance with 250.140(B). (A) Equipment Grounding Conductor Connections. The circuit supplying the appliance shall include an equipment grounding conductor. The frame of the appliance shall be connected to the equipment grounding conductor in the manner specified by 250.134 or 250.138. (B) Grounded Conductor Connections. For existing branch-circuit installations only, if an equipment grounding conductor is not present in the outlet or junction box the frame of the appliance shall be permitted to be connected to the grounded conductor if all the conditions in the following list items (1), (2), and (3) are met and the grounded conductor complies with either list item (4) or (5): * (1) 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. * (2) The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum or copper-clad aluminum. * (3) Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment. * (4) 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. * (5) The grounded conductor is part of a Type SE service-entrance cable that originates in equipment other than a service. The grounded conductor shall be insulated or field covered within the supply enclosure with listed insulating material, such as tape or sleeving to prevent contact of the uninsulated conductor with any normally non-current-carrying metal parts. ENHANCED CONTENT Collapse Prior to the 1996 edition of the NEC, use of the grounded circuit conductor as a grounding conductor was permitted for range installations. In many instances, the wiring method was service-entrance cable with an uninsulated neutral conductor covered by the cable jacket. Where Type SE cable was used to supply ranges and dryers, the branch circuit was required to originate at the service equipment to avoid neutral current from downstream panelboards being imposed on metal objects, such as pipes or ducts. The grounded conductor (neutral) of newly installed branch circuits supplying ranges and clothes dryers is not permitted to be used for grounding the non-current- carrying metal parts of the appliances. Branch circuits for new appliance installations are required to provide an EGC sized in accordance with 250.122 for grounding the non-current-carrying metal parts. An older appliance connected to a new branch circuit must have its 3-wire cord and plug replaced with a 4-conductor cord, with one of those conductors being an EGC. The appliance bonding jumper between the neutral and the frame of the appliance must be removed. Where a new range or clothes dryer is connected to an existing branch circuit without an EGC, an appliance bonding jumper must be connected between the neutral terminal and the frame of the appliance. The grounded circuit conductor of an existing branch circuit is permitted to be used to ground the frame of an electric range, wall-mounted oven, or counter- mounted cooking unit, provided the conditions in 250.140(B)(1), (2), and (3) are all met, and one of either (4) or (5) is met. In addition, the grounded circuit conductor of the existing branch circuits is also permitted to be used to ground any junction boxes in the circuit supplying the appliance, and a 3-wire pigtail and range receptacle are permitted to be used. 250.142 Use of Grounded Circuit Conductor for Grounding Equipment. (A) Supply-Side Equipment. A grounded circuit conductor shall be permitted to be connected to non- current-carrying metal parts of equipment, raceways, and other enclosures at any of the following locations: * (1) On the supply side or within the enclosure of the ac service disconnecting means * (2) On the supply side or within the enclosure of the main disconnecting means for separate buildings as provided in 250.32(B)(1) Exception No. 1 * (3) On the supply side or within the enclosure of the main disconnecting means or overcurrent devices of a separately derived system where permitted by 250.30(A)(1) (B) Load-Side Equipment. Except as permitted in 250.30(A)(1), 250.32(B)(1), Exception No. 1, and Part X of Article 250, a grounded circuit conductor shall not be connected to non- current-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, counter-mounted cooking units, and clothes dryers under the conditions permitted for existing installations by 250.140 shall be permitted to be connected to the grounded circuit conductor. Exception No. 2: It shall be permissible to connect meter enclosures to the grounded circuit conductor on the load side of the service disconnect if all of the following conditions apply: * (1) Ground-fault protection of equipment is not installed. * (2) All meter enclosures are located immediately adjacent to the service disconnecting means. * (3) The size of the grounded circuit conductor is not smaller than the size specified in Table 250.122 for equipment grounding conductors. Exception No. 3: Electrode-type boilers operating at over 1000 volts shall be grounded as required in 495.72(E)(1) and 495.74. ENHANCED CONTENT Collapse If the grounded circuit conductor is re-grounded on the load side of the service and the grounded conductor is disconnected at any point on the line side of the service, the EGC and all conductive parts connected to it would become energized. Under this condition, the potential to ground of any exposed metal parts could be raised to line voltage. This rise in potential on noncurrent-carrying conductive parts could result in arcing in concealed spaces and could pose a severe shock hazard, particularly if contact is made with metal piping or ductwork. Even without an open grounded conductor, a connection between the grounded conductor and the EGC on the load side of the service places the EGC in a parallel circuit path with the grounded conductor. Exposed and concealed non-current-carrying metal parts could also be hazardous. See also 250.30(A)(3) and 250.32(B), which prohibit the creation of parallel paths for normal neutral current. 250.144 Multiple Circuit Connections. If equipment is required to be grounded and is supplied by more than one circuit containing an equipment grounding conductor, a means to terminate each equipment grounding conductor meeting the requirements of 250.8 shall be provided as specified in 250.134 and 250.138. 250.146 Connecting Receptacle Grounding Terminal to an Equipment Grounding Conductor. An equipment bonding jumper shall be used to connect the grounding terminal of a grounding-type receptacle to a metal box that is connected to an equipment grounding conductor, except as permitted in 250.146(A) through (D). The equipment bonding jumper shall be sized in accordance with Table 250.122. (A) Surface-Mounted Box. If a metal box is mounted on the surface, the direct metal-to-metal contact between the device yoke or strap to the box shall be permitted to provide the required effective ground-fault current path. At least one of the insulating washers shall be removed from receptacles that do not have a contact yoke or device to ensure direct metal-to-metal contact. Direct metal-to-metal contact for providing continuity applies to cover-mounted receptacles if the box and cover combination are listed as providing continuity between the box and the receptacle. A listed exposed work cover shall be permitted to be the grounding and bonding means under both of the following conditions: * (1) The device is attached to the cover with at least two fasteners that are permanent (such as a rivet) or have a thread-locking or screw- or nut- locking means. * (2) The cover mounting holes are located on a flat nonraised portion of the cover. ENHANCED CONTENT Collapse Section 250.146(A) permits the equipment bonding jumper to be omitted where the metal yoke of the device is in direct metal-to-metal contact with the metal device box and at least one of the fiber retention washers for the receptacle mounting screws is removed, as illustrated below. Box-cover and device combinations listed as providing grounding continuity are permitted, as pictured below. The mounting holes for the cover must be located on a flat, non-raised portion of the cover to provide the best possible surface-to-surface contact, and the receptacle must be secured to the cover using not less than two rivets or locking means for threaded attachment means. Contact Devices or Yokes. Contact devices or yokes designed and listed as self-grounding shall be permitted in conjunction with the supporting screws to establish equipment bonding between the device yoke and flush-type boxes. ENHANCED CONTENT Collapse Shown below is a listed self-grounding receptacle designed with a pressure spring clip that secures the top upper device mounting screw to establish a bonding connection between the receptacle and a grounded metal box. This connection eliminates the need for a wire-type equipment bonding jumper installed from the grounded metal box to the receptacle grounding terminal. Such devices are listed as “self-grounding” and are permitted to be used for bonding a flush-mounted receptacle to a grounded metal box. (Photo courtesy of Leviton Manufacturing Co., Inc.) (C) Floor Boxes. Floor boxes designed for and listed as providing continuity between the box and the device shall be permitted. (D) Isolated Ground Receptacles. If installed for the reduction of electromagnetic interference on the equipment grounding conductor, a receptacle in which the grounding terminal is purposely insulated from the receptacle mounting means shall be permitted. The receptacle grounding terminal shall be connected to an insulated equipment grounding conductor run with the circuit conductors. This equipment grounding conductor shall be permitted to pass through one or more panelboards without a connection to the panelboard grounding terminal bar as permitted in 408.40, 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. If installed in accordance with this section, this equipment grounding conductor shall also be permitted to pass through boxes, wireways, or other enclosures without being connected to such enclosures. Informational Note: Use of an isolated equipment grounding conductor does not relieve the requirement for connecting the raceway system and outlet box to an equipment grounding conductor. ENHANCED CONTENT Collapse An isolated-ground-type receptacle is permitted to be installed without a bonding jumper between the metal device box and the receptacle grounding terminal. However, the isolated EGC must provide an effective path for ground-fault current between the receptacle grounding terminal and the source of the branch circuit supplying the receptacle. An insulated EGC, as shown in the exhibit below, is installed with the branch-circuit conductors. This conductor can originate in the service panel, pass through any number of subpanels without being connected to the equipment grounding bus, and terminate at the isolated-ground-type receptacle ground terminal. Termination of the isolated EGC at the service is not necessary. It can be terminated at any of the intervening panelboards. The objective is to terminate it where the noise is eliminated. This isolated EGC arrangement does not exempt the metal device box from being grounded. The metal device box must be grounded either by an EGC run with the circuit conductors or by a wiring method that serves as an EGC. According to 250.146(D), where isolated-ground-type receptacles are used, the isolated EGC can terminate at an equipment grounding terminal of the applicable service or derived system in the same building as the receptacle. If the isolated EGC terminates at a separate building, a large voltage difference could exist between buildings during lightning transients. Such transients could cause damage to equipment connected to an isolated-ground-type receptacle and present a shock hazard between the isolated equipment frame and other grounded surfaces. 250.148 Continuity of Equipment Grounding Conductors and Attachment in Boxes. If circuit conductors are spliced within a box or terminated on equipment within or supported by a box, the installation shall comply with 250.148(A) through (D). Exception: The equipment grounding conductor permitted in 250.146(D) shall not be required to be connected to the other equipment grounding conductors or to the box. ENHANCED CONTENT Collapse If multiple circuits are spliced within the box or terminated to equipment within the box, all the EGCs must be connected together and to the box unless exempted under 250.148. If a metal box is grounded by a metal raceway system and the circuit conductors are not spliced or terminated to equipment in the metal box, the wire-type EGC is not required to be connected to the box. Wire-type EGCs that are not spliced or terminated within a box do not have to be connected to the box; however, the box (if metal) is required to be connected to the EGC of the circuit with the highest rating that is contained in the box. (A) Connections and Splices. All equipment grounding conductors that are spliced or terminated within the box shall be connected together. Connections and splices shall be made in accordance with 110.14(B) and 250.8 except that insulation shall not be required. (B) Equipment Grounding Conductor Continuity. The arrangement of grounding connections shall be such that the disconnection or the removal of a luminaire, receptacle, or other device fed from the box does not interrupt the electrical continuity of the equipment grounding conductor(s) providing an effective ground-fault current path. (C) Metal Boxes. A connection used for no other purpose shall be made between the metal box and the equipment grounding conductor(s). The equipment bonding jumper or equipment grounding conductor shall be sized from Table 250.122 based on the largest overcurrent device protecting circuit conductors in the box. (D) Nonmetallic Boxes. One or more equipment grounding conductors brought into a nonmetallic outlet box shall be arranged to provide a connection to any fitting or device in that box requiring connection to an equipment grounding conductor. Part VIII. Direct-Current Systems 250.160 General. Direct-current systems shall comply with Part VIII and other sections of Article 250 not specifically intended for ac systems. 250.162 Direct-Current Circuits and Systems to Be Grounded. Direct-current circuits and systems shall be grounded as provided for in 250.162(A) and (B). (A) Two-Wire, Direct-Current Systems. A 2-wire, dc system supplying premises wiring and operating at greater than 60 volts but not greater than 300 volts shall be grounded. Exception No. 1: A system equipped with a ground detector and supplying only industrial equipment in limited areas shall not be required to be grounded if installed immediately adjacent to, or integral with, the source of supply. Exception No. 2: A rectifier-derived dc system supplied from an ac system complying with 250.20 shall not be required to be grounded. Exception No. 3: Direct-current fire alarm circuits having a maximum current of 0.030 ampere as specified in Article 760, Part III, shall not be required to be grounded. (B) Three-Wire, Direct-Current Systems. The neutral conductor of all 3-wire, dc systems supplying premises wiring shall be grounded. 250.164 Point of Connection for Direct-Current Systems. (A) Off-Premises Source. Direct-current systems to be grounded and supplied from an off-premises source shall have the grounding connection made at one or more supply stations. A grounding connection shall not be made at individual services or at any point on the premises wiring. (B) On-Premises Source. If the dc system source is located on the premises, a grounding connection shall be made at one of the following: * (1) The source * (2) The first system disconnection means or overcurrent device * (3) By other means that accomplish system protection and that use equipment listed and identified for the use 250.166 Size of the Direct-Current Grounding Electrode Conductor. The size of the grounding electrode conductor for a dc system shall be as specified in 250.166(A) and (B), except as permitted by 250.166(C) through (E). The grounding electrode conductor for a dc system shall meet the sizing requirements in this section but shall not be required to be larger than 3/0 copper or 250 kcmil aluminum or copper-clad aluminum. (A) Not Smaller Than the Neutral Conductor. If the dc system consists of a 3-wire balancer set or a balancer winding with overcurrent protection as provided in 445.12(D), the grounding electrode conductor shall not be smaller than the neutral conductor and not smaller than 8 AWG copper or 6 AWG aluminum or copper-clad aluminum. (B) Not Smaller Than the Largest Conductor. If the dc system is other than as in 250.166(A), the grounding electrode conductor shall not be smaller than the largest conductor supplied by the system and not smaller than 8 AWG copper or 6 AWG aluminum or copper- clad aluminum. (C) Connected to Rod, Pipe, or Plate Electrodes. If connected to rod, pipe, or plate electrodes as in 250.52(A)(5) or (A)(7), that portion of the grounding electrode conductor that is the sole connection to the grounding electrode shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum or copper-clad aluminum wire. (D) Connected to a Concrete-Encased Electrode. If connected to a concrete-encased electrode as in 250.52(A)(3), that portion of the grounding electrode conductor that is the sole connection to the grounding electrode shall not be required to be larger than 4 AWG copper wire. (E) Connected to a Ground Ring. If connected to a ground ring as in 250.52(A)(4), that portion of the grounding electrode conductor that is the sole connection to the grounding electrode shall not be required to be larger than the conductor used for the ground ring. 250.167 Direct-Current Ground-Fault Detection. (A) Ungrounded Systems. Ground-fault detection systems shall be required for ungrounded systems. (B) Grounded Systems. Ground-fault detection shall be permitted for grounded systems. (C) Marking. Direct-current systems shall be legibly marked to indicate the grounding type at the dc source or the first disconnecting means of the system. The marking shall be of sufficient durability to withstand the environment involved. Informational Note: See NFPA 70E -2018, Standard for Electrical Safety in the Workplace, which identifies four dc grounding types in detail. 250.168 Direct-Current System Bonding Jumper. For direct-current systems that are to be grounded, an unspliced bonding jumper shall be used to connect the equipment grounding conductor(s) to the grounded conductor at the source or to the first system disconnecting means where the system is grounded. The size of the bonding jumper shall not be smaller than the system grounding electrode conductor specified in 250.166 and shall comply with 250.28(A), (B), and (C). 250.169 Ungrounded Direct-Current Separately Derived Systems. Except as otherwise permitted in 250.34 for portable and vehicle-mounted generators, an ungrounded dc separately derived system supplied from a stand-alone power source (such as an engine-generator set) shall have a grounding electrode conductor connected to an electrode that complies with Part III of this article to provide for grounding of metal enclosures, raceways, cables, and exposed non-current-carrying metal parts of equipment. The grounding electrode conductor connection shall be to the metal enclosure at any point on the separately derived system from the source to the first system disconnecting means or overcurrent device, or it shall be made at the source of a separately derived system that has no disconnecting means or overcurrent devices. The size of the grounding electrode conductor shall be in accordance with 250.166. P