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250.4, 2023 Code Cycle Public Input, Ungrounded Metal Components

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    250.4, 2023 Code Cycle Public Input, Ungrounded Metal Components



    I am seeking comment, guidance and correction on this Public Input that I am considering submitting next code cycle.



    Public Input

    1.) Section
    250.4


    2.) Revised Text

    250.4 General Requirements for Grounding and Bonding. The following general requirements identify what grounding and bonding of electrical systems are required to accomplish. The prescriptive methods contained in Article 250 shall be followed to comply with the performance requirements of this section.

    (A) Grounded Systems.
    (1) Electrical System Grounding.
    Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

    Informational Note No. 1: An important consideration for limiting the imposed voltage is the routing of bonding and grounding electrode conductors so that they are not any longer than necessary to complete the connection without disturbing the permanent parts of the installation and so that unnecessary bends and loops are avoided. Informational Note No. 2: See NFPA 780-2014, Standard for the Installation of Lightning Protection Systems, for information on



    (2) Grounding of Electrical Equipment. Normally non– current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage to ground on these materials, unless specifically permitted elsewhere in this code.


    (3) Bonding of Electrical Equipment. Normally non–current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path, unless specifically permitted elsewhere in this code.


    (4) Bonding of Electrically Conductive Materials and Other Equipment. Normally non–current-carrying electrically conductive materials that are likely to become energized shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path, unless specifically permitted elsewhere in this code.


    (5) Effective Ground-Fault Current Path. Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur, unless specifically permitted elsewhere in this code.


    (B) Ungrounded Systems.
    (1) Grounding Electrical Equipment. Non–current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth in a manner that will limit the voltage imposed by lightning or unintentional contact with higher-voltage lines and limit the voltage to ground on these materials, unless specifically permitted elsewhere in this code.


    Informational Note: See NFPA 780-2014, Standard for the Installation of Lightning Protection Systems, for information on installation of grounding and bonding for lightning protection systems.


    (2) Bonding of Electrical Equipment. Non–current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying the maximum fault current likely to be imposed on it, unless specifically permitted elsewhere in this code.


    (3) Bonding of Electrically Conductive Materials and Other Equipment. Electrically conductive materials that are likely to become energized shall be connected together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying the maximum fault current likely to be imposed on it, unless specifically permitted elsewhere in this code.


    (4) Path for Fault Current. Electrical equipment, wiring, and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit from any point on the wiring system to the electrical supply source to facilitate the operation of overcurrent devices should a second ground fault from a different phase occur on the wiring system, unless specifically permitted elsewhere in this code. The earth shall not be considered as an effective fault-current path .





    3.) Proposed new wording
    The only change is the addition of the phrase ", unless specifically permitted elsewhere in this code" in eight of the paragraphs in the section.


    4.)Substantiation
    4A.)The problem that is being resolved

    Currently the existing language is a contradiction to later sections in the same article. Currently the language in this section strictly states all associated metal that is enclosing conductors or equipment must be grounded and bonded, later sections such as 250.80 exception, 250.86 exceptions 1, 2 and 3, 250.110 exceptions 1, 2 and 3, and 250.112(D), (F) and (I) contradict the strict statements of 250.4 and allow equipment to not be grounded or bonded.


    4B.)How will this revision solve the problem
    This revision will align the section with the rest of the article and eliminate the contradiction, adding to the usability and readability of the code.

    #2
    4C.)Code Sections Referenced in my Substantiation ( 4A.The Problem That is Being Resolved)


    250.80 Service Raceways and Enclosures. Metal enclosures and raceways for service conductors and equipment shall be connected to the grounded system conductor if the electrical system is grounded or to the grounding electrode conductor for electrical systems that are not grounded.

    Exception: Metal components that are installed in a run of underground nonmetallic raceway(s) and are isolated from possible contact by a minimum cover of 450 mm (18 in.) to all parts of the metal components shall not be required to be connected to the grounded system conductor, supply side bonding jumper, or grounding electrode conductor.

    250.86 Other Conductor Enclosures and Raceways. Except as permitted by 250.112(I), metal enclosures and raceways for other than service conductors shall be connected to the equipment grounding conductor.

    Exception No. 1: Metal enclosures and raceways for conductors added to existing installations of open wire, knob-and-tube wiring, and nonmetallic-sheathed cable shall not be required to be connected to the equipment grounding conductor where these enclosures or wiring methods comply with (1) through (4) as follows:
    (1) Do not provide an equipment ground
    (2) Are in runs of less than 7.5 m (25 ft)
    (3) Are free from probable contact with ground, grounded metal, metal lath, or other conductive material
    (4) Are guarded against contact by persons

    Exception No. 2: Short sections of metal enclosures or raceways used to provide support or protection of cable assemblies from physical damage shall not be required to be connected to the equipment grounding conductor.

    Exception No. 3: Metal components shall not be required to be connected to the equipment grounding conductor or supply-side bonding jumper where either of the following conditions exist:

    (1) The metal components are installed in a run of nonmetallic raceway(s) and isolated from possible contact by a minimum cover of 450 mm (18 in.) to any part of the metal components.


    (2) The metal components are part of an installation of nonmetallic raceway(s) and are isolated from possible contact to any part of the metal components by being encased in not less than 50 mm (2 in.) of concrete.


    Part VI. Equipment Grounding and Equipment Grounding Conductors
    250.110 Equipment Fastened in Place (Fixed) or Connected by Permanent Wiring Methods. Exposed, normally non–current carrying metal parts of fixed equipment supplied by or enclosing conductors or components that are likely to become energized shall be connected to an equipment grounding conductor under any of the following conditions:
    (1) Where within 2.5 m (8 ft) vertically or 1.5 m (5 ft) horizontally of ground or grounded metal objects and subject to contact by persons
    (2) Where located in a wet or damp location and not isolated
    (3) Where in electrical contact with metal
    (4) Where in a hazardous (classified) location as covered by Articles 500 through 517
    (5) Where supplied by a wiring method that provides an equipment grounding conductor, except as permitted by 250.86, Exception No. 2, for short sections of metal enclosures
    (6) Where equipment operates with any terminal at over 150 volts to ground

    Exception No. 1: If exempted by special permission, the metal frame of electrically heated appliances that have the frame permanently and effectively insulated from ground shall not be required to be grounded.


    Exception No. 2: Distribution apparatus, such as transformer and capacitor cases, mounted on wooden poles at a height exceeding 2.5 m (8 ft) above ground or grade level shall not be required to be grounded.


    Exception No. 3: Listed equipment protected by a system of double insulation, or its equivalent, shall not be required to be connected to the equipment grounding conductor. Where such a system is employed, the equipment shall be distinctively marked.


    250.112 Specific Equipment Fastened in Place (Fixed) or Connected by Permanent Wiring Methods. Except as permitted in 250.112(F) and (I), exposed, normally non–current-carrying metal parts of equipment described in 250.112(A) through (K), and normally non–current-carrying metal parts of equipment and enclosures described in 250.112(L) and (M), shall be connected to an equipment grounding conductor, regardless of voltage.
    (A) Switchgear and Switchboard Frames and Structures. Switchgear or switchboard frames and structures supporting switching equipment, except frames of 2-wire dc switchgear or switchboards where effectively insulated from ground.
    (B) Pipe Organs. Generator and motor frames in an electrically operated pipe organ, unless effectively insulated from ground and the motor driving it.
    (C) Motor Frames. Motor frames, as provided by 430.242.
    (D) Enclosures for Motor Controllers. Enclosures for motor controllers unless attached to ungrounded portable equipment.
    (E) Elevators and Cranes. Electrical equipment for elevators and cranes.
    (F) Garages, Theaters, and Motion Picture Studios. Electrical equipment in commercial garages, theaters, and motion picture studios, except pendant lampholders supplied by circuits not over 150 volts to ground.
    (G) Electric Signs. Electric signs, outline lighting, and associated equipment as provided in 600.7.
    (H) Motion Picture Projection Equipment. Motion picture projection equipment.
    (I) Remote-Control, Signaling, and Fire Alarm Circuits. Equipment supplied by Class 1 circuits shall be grounded unless operating at less than 50 volts. Equipment supplied by Class 1 power-limited circuits, by Class 2 and Class 3 remote control and signaling circuits, and by fire alarm circuits shall be grounded where system grounding is required by Part II or Part VIII of this article.
    (J) Luminaires. Luminaires as provided in Part V of Article 410.
    (K) Skid-Mounted Equipment. Permanently mounted electrical equipment and skids shall be connected to the equipment grounding conductor sized as required by 250.122.
    (L) Motor-Operated Water Pumps. Motor-operated water pumps, including the submersible type.
    (M) Metal Well Casings. Where a submersible pump is used in a metal well casing, the well casing shall be connected to the pump circuit equipment grounding conductor.

    Comment


      #3
      EXTENDED 4C.)Code Sections Referenced in my Substantiation ( 4A.The Problem That is Being Resolved)



      250.114 Equipment Connected by Cord and Plug.
      Under any of the conditions described in 250.114(1) through (4), exposed, normally non–current-carrying metal parts of cord-and-plug-connected equipment shall be connected to the equipment grounding conductor.
      Exception: Listed tools, listed appliances, and listed equipment covered in 250.114(2) through (4) shall not be required to be connected to an equipment grounding conductor where protected by a system of double insulation or its equivalent. Double insulated equipment shall be distinctively marked.

      (1) In hazardous (classified) locations (see Articles 500 through 517)

      (2) Where operated at over 150 volts to ground

      Exception No. 1: Motors, where guarded, shall not be required to be connected to an equipment grounding conductor.

      Exception No. 2: Metal frames of electrically heated appliances, exempted by special permission, shall not be required to be connected to an equipment grounding conductor, in which case the frames shall be permanently and effectively insulated from ground.

      (3) In residential occupancies:
      a. Refrigerators, freezers, and air conditioners
      b. Clothes-washing, clothes-drying, dish-washing machines; ranges; kitchen waste disposers; information technology equipment; sump pumps and electrical aquarium equipment
      c. Hand-held motor-operated tools, stationary and fixed motor-operated tools, and light industrial motoroperated tools
      d. Motor-operated appliances of the following types: hedge clippers, lawn mowers, snow blowers, and wet scrubbers
      e. Portable handlamps

      (4) In other than residential occupancies:
      a. Refrigerators, freezers, and air conditioners
      b. Clothes-washing, clothes-drying, dish-washing machines; information technology equipment; sump pumps and electrical aquarium equipment
      c. Hand-held motor-operated tools, stationary and fixed motor-operated tools, and light industrial motoroperated tools
      d. Motor-operated appliances of the following types: hedge clippers, lawn mowers, snow blowers, and wet scrubbers
      e. Portable handlamps
      f. Cord-and-plug-connected appliances used in damp or wet locations or by persons standing on the ground or on metal floors or working inside of metal tanks or boilers
      g. Tools likely to be used in wet or conductive locations

      Exception: Tools and portable handlamps likely to be used in wet or conductive locations shall not be required to be connected to an equipment grounding conductor where supplied through an isolating transformer with an ungrounded secondary of not over 50 volts.

      Comment


        #4
        I take it you all don't care much for the proposal. Below is my latest revision if it makes a difference, I consolidated paragraphs and changed the language to what I think reads a little better. Any input is appreciated.


        2.) Revised Text


        250.4 General Requirements for Grounding and Bonding. The following general requirements identify what grounding and bonding of electrical systems are required to accomplish. The prescriptive methods contained in Article 250 shall be followed to comply with the performance requirements of this section.


        (A) Grounded Systems, Grounding and Bonding of Electrical Equipment and Normally Non-Current-Carrying Conductive Materials. Except where specifically permitted otherwise in this code, normally non–current-carrying conductive materials enclosing electrical conductors or equipment, and normally non–current-carrying conductive materials that are likely to become energized shall be:

        (1) Connected to earth in a manner that will limit the voltage imposed by lightning or unintentional contact with higher-voltage lines and limit the voltage to ground on these materials.
        (2) Connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.
        (3) Installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur

        Informational Note No. 1: An important consideration for limiting the imposed voltage is the routing of bonding and grounding electrode conductors so that they are not any longer than necessary to complete the connection without disturbing the permanent parts of the installation and so that unnecessary bends and loops are avoided.

        Informational Note No. 2: See NFPA 780-2014, Standard for the Installation of Lightning Protection Systems, for information oninstallation of grounding and bonding for lightning protection systems.



        (B) Ungrounded Systems, Grounding and Bonding of Electrical Equipment and Normally Non-Current-Carrying Conductive Materials. Except where specifically permitted otherwise in this code, normally non–current-carrying conductive materials enclosing electrical conductors or equipment, and normally non–current-carrying conductive materials that are likely to become energized shall be:

        (1) Connected to earth in a manner that will limit the voltage imposed by lightning or unintentional contact with higher-voltage lines and limit the voltage to ground on these materials.
        (2) Connected together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying the maximum fault current likely to be imposed on it.
        (3) Installed in a manner that creates a low-impedance circuit between any two points on the wiring system to facilitate the operation of overcurrent devices should a second ground fault from a different phase occur on the wiring system. The earth shall not be considered as an effective fault-current path .


        Informational Note: See NFPA 780-2014, Standard for the Installation of Lightning Protection Systems, for information on installation of grounding and bonding for lightning protection systems.

        Comment


          #5
          In case you skipped to the last post, I revised my original proposal and the latest is in the post just previous to this one.

          3.)Here is the existing NEC (2020 and 2017) Text


          250.4 General Requirements for Grounding and Bonding.
          The following general requirements identify what grounding and bonding of electrical systems are required to accomplish. The prescriptive methods contained in Article 250 shall be followed to comply with the performance requirements of this section.

          (A) Grounded Systems.


          (1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

          Informational Note No. 1: An important consideration for limiting the imposed voltage is the routing of bonding and grounding electrode conductors so that they are not any longer than necessary to complete the connection without disturbing the permanent parts of the installation and so that unnecessary bends and loops are avoided.

          Informational Note No. 2: See NFPA 780-2014, Standard for the Installation of Lightning Protection Systems, for information oninstallation of grounding and bonding for lightning protection systems.

          (2) Grounding of Electrical Equipment. Normally non– current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage to ground on these materials.

          (3) Bonding of Electrical Equipment.
          Normally non–currentcarrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.

          (4) Bonding of Electrically Conductive Materials and Other Equipment.
          Normally non–current-carrying electrically conductive materials that are likely to become energized shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.

          (5) Effective Ground-Fault Current Path.
          Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be considered as an effective ground-fault current path.

          (B) Ungrounded Systems.

          (1) Grounding Electrical Equipment.
          Non–current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth in a manner that will limit the voltage imposed by lightning or unintentional contact with higher-voltage lines and limit the voltage to ground on these materials.

          Informational Note: See NFPA 780-2014, Standard for the Installation of Lightning Protection Systems, for information on installation of grounding and bonding for lightning protection systems.

          (2) Bonding of Electrical Equipment. Non–current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying the maximum fault current likely to be imposed on it.

          (3) Bonding of Electrically Conductive Materials and Other Equipment.
          Electrically conductive materials that are likely to become energized shall be connected together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying the maximum fault current likely to be imposed on it.

          (4) Path for Fault Current.
          Electrical equipment, wiring, and other electrically conductive material likely to become energized shall be installed in a manner that creates a lowimpedance circuit from any point on the wiring system to the electrical supply source to facilitate the operation of overcurrent devices should a second ground fault from a different phase occur on the wiring system. The earth shall not be considered as an effective fault-current path.

          Comment


            #6
            Sorry, I missed something ((A)(1)). And again, any input is appreciated.

            2.) Revised Text (revision 3)



            250.4 General Requirements for Grounding and Bonding. The following general requirements identify what grounding and bonding of electrical systems are required to accomplish. The prescriptive methods contained in Article 250 shall be followed to comply with the performance requirements of this section.

            (A) Grounded Systems

            (1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

            Informational Note No. 1: An important consideration for limiting the imposed voltage is the routing of bonding and grounding electrode conductors so that they are not any longer than necessary to complete the connection without disturbing the permanent parts of the installation and so that unnecessary bends and loops are avoided.

            Informational Note No. 2: See NFPA 780-2014, Standard for the Installation of Lightning Protection Systems, for information oninstallation of grounding and bonding for lightning protection systems.


            (2)Grounding and Bonding of Electrical Equipment and Normally Non-Current-Carrying Conductive Materials. Except where specifically permitted otherwise in this code, normally non–current-carrying conductive materials enclosing electrical conductors or equipment, and normally non–current-carrying conductive materials that are likely to become energized shall be:

            (1) Connected to earth in a manner that will limit the voltage imposed by lightning or unintentional contact with higher-voltage lines and limit the voltage to ground on these materials.
            (2) Connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.
            (3) Installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur


            (B) Ungrounded Systems, Grounding and Bonding of Electrical Equipment and Normally Non-Current-Carrying Conductive Materials. Except where specifically permitted otherwise in this code, normally non–current-carrying conductive materials enclosing electrical conductors or equipment, and normally non–current-carrying conductive materials that are likely to become energized shall be:

            (1) Connected to earth in a manner that will limit the voltage imposed by lightning or unintentional contact with higher-voltage lines and limit the voltage to ground on these materials.
            (2) Connected together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying the maximum fault current likely to be imposed on it.
            (3) Installed in a manner that creates a low-impedance circuit between any two points on the wiring system to facilitate the operation of overcurrent devices should a second ground fault from a different phase occur on the wiring system. The earth shall not be considered as an effective fault-current path .


            Informational Note: See NFPA 780-2014, Standard for the Installation of Lightning Protection Systems, for information on installation of grounding and bonding for lightning protection systems.
            Last edited by Devin Hanes; 07-10-19, 09:38 PM.

            Comment

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