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    Bonding of Neutral to Ground ... Where? Where not?

    Bonding of Neutral to Ground ... Where? Where not?

    New postby Jerry Peck - Codeman on Sun Dec 07, 2014 4:33 pm

    History of grounded conductor (neutral) and grounding conductor (ground) connection and the location of such connection:

    From the 1897 "Rules and Requirements of the Underwriters' Association of the Middle Department for the Installation of Wiring and Apparatus for Light, Heat and Power" Adopted August 31, 1897.

    Note: The above book is recognized as the first "National Electrical Code" even though "National Electrical Code" is not in its title. I also have a 1905 edition of the book and the name "National Electrical Code." is above the full name shown above.

    The 1897 National Electrical Code (NEC) does not address grounding in much detail as, at that time, there were direct-current (DC) circuits and alternating-current (AC) circuits, with recommendations for DC circuits to be wired for conversion to AC circuits and grounding of DC circuits is treated differently than that of AC circuits, and, grounding was not well understood as a safety factor at that time.

    The 1897 NEC does, however, reference conductors being required to be insulated to protect the conductors from each other and from ground - and that protection of conductors from ground leads to the first reference is isolating conductors, including the grounded (neutral) conductor, from ground.
    - Class E.
    - - Miscellaneous.
    - - - 44. Insulation Resistance-
    - - - - The wiring in any building must test free from grounds, i.e., the complete installation must have an insulation between conductors and between all conductors and the ground (not including attachments, sockets, receptacles, etc.) of not less than the following:-
    - - - - - Up to 5 amperes ..... 4,000,000
    - - - - - Up to 10 amperes .... 2,000,000
    - - - - - (the list continues to 1,600 amperes)
    - - - - All cut-outs and safety devices in place in the above.
    - - - - Where lamp sockets, receptacles and electroliers, etc., are connected, one half of the above will be required.

    The above means that a two-wire non-grounding circuit, both conductors (which we now call the "ungrounded" or "hot" conductor and "grounded" or "neutral" conductor) shall not be insulated from ground (not connected to ground).

    "Grounding" is addressed in the 1987 NEC in various sections (albeit in a limited number of sections), such as this section:
    - 29. Interior Conduits-
    - - (general section text)
    - - - a. Must be continuous from one junction box to another or to fixtures, and the conduit tube must properly enter all fittings.
    - - - b. Must be installed as a complete conduit system, without the conductors.
    - - - c. Conduits must extend ... (continues with too much to type here)
    - - - d. Metal conduits, where they enter junction boxes, and at all other outlets, etc., must be fitted with a capping of approved insulation material, fitted so as to protect wire from abrasion.
    - - - e. Must have the metal of the conduit permanently and effectually grounded.
    - - - f. (continues on through 0., however, my reason for including this section was about the requirement to be grounded, as in e.)

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    From the aforementioned 1905 NEC: (bold text and italic text is in the 1905 NEC as bold text and italic text)
    - 13 A. Grounding Low-Potential Circuits.
    - - The grounding of low-potential circuits under the following regulations is only allowed when such circuits are so arranged that under normal conditions of service there will be no passage of current over the ground wire.
    - - Direct-current 3-Wire Systems.
    - - - a. (text not included as it does not relate to the discussion)
    - - Alternating-Current Secondary Systems.
    - - - b. (text not included as it does not relate to the discussion)
    - - - c. (text not included as it does not relate to the discussion)
    - - - d. (text not included as it does not relate to the discussion)
    - - - e. (text not included as it does not relate to the discussion)
    - - - f. The ground connection for Central Stations, transformer substations, and banks of transformers must be made through metal plates buried in code below permanent moisture level, and underground piping systems including the lead sheath of underground cables.
    - - - g. For individual transformers and building services the ground connection may be made as in Section f, or may be made to water or other piping systems running into the buildings. This connection may be made by carrying the ground wire into the cellar and connecting on the street side of meters, main cocks, etc., but connection must never be made to any lead pipes which form part of gas services.

    The 1905 NEC addresses grounding slightly more than the 1987 NEC, but the key part is this part:
    - 13 A. Grounding Low-Potential Circuits.
    - - The grounding of low-potential circuits under the following regulations is only allowed when such circuits are so arranged that under normal conditions of service there will be no passage of current over the ground wire.

    The way to achieve "no passage of current over the ground wire" is not isolate the neutral conductor (which is now a "grounded conductor) from the grounding conductors and ground. The neutral conductor (now the grounded conductor) can be connected to ground (which we now call bonding or bonded to ground) was permitted at the transformer as provided for in section f, or from the service to the metal piping being used as what we now call the grounding electrode.

    The neutral could thus be grounded at the service equipment or at the transformer, but not downstream of the service equipment.

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    I had a 1915 NEC ... however, I can no longer find it (I loaned it out and forgot who I loaned it to - oh well).

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    The 1925 NEC addressed ground much better, as each newer edition of the NEC did as understanding of the importance of grounding grew. From the 1925 NEC:
    - 902 Distribution Systems.
    - - a. Two-wire direct-current systems shall be grounded as provided herein ... (not applicable to this discussion)
    - - b. Three-wire direct-current systems shall be grounded as provided herein ... (not applicable to this discussion)
    - - c. Alternating current systems shall be grounded as provided in this article, if the maximum difference of potential between the grounded point and any other point on the circuit does not exceed 150 volts. Electric furnace circuits need not be grounded.
    - - - (what amounts to a FPN , now known as Informational Note, follows c. - "It is recommended that such systems also be grounded as provided here, if the difference of potential exceeds 150 volts but does not exceed 300 volts.)
    - - d. On single phase alternating current systems the ground shall be made at each service on the line side of the service switch before the service is connected to the line. On multiphase alternating current systems the ground shall be as described for single phase systems if the grounded conductor of the multiphase supply system is brought to the premises for rendering service. By permission of the inspection department the grounding connection for either single phase or multiphase systems may be made on or near the transformer or transformers, or by connection to a system ground wire.
    - - e. (text addresses where in the system the system is grounded, i.e., at the point where the system brings about the lowest voltage from ground, etc., it does not address location on the premises)
    - - f.(text addresses where in the system the system is grounded, i.e., at the point where the system brings about the lowest voltage from ground, etc., it does not address location on the premises)
    - - g.(text addresses where in the system the system is grounded, i.e., at the point where the system brings about the lowest voltage from ground, etc., it does not address location on the premises)
    - - h.The grounded conductor of an interior wiring system shall have but one grounding connection within the building, except as provided in paragraph b of section 906 of this article.

    - 906. Ground connections
    - - b. At supply stations, grounding conductor for circuits, equipment and lightning arresters shall be permanently and effectively connected to all available active, continuous, metallic underground piping systems between which no appreciable difference of potential normally exists; otherwise to one system only. Elsewhere than at supply stations, the grounding conductor shall be connected to at least one such piping system, if available. Gas piping shall be avoided wherever practicable, except as provide in paragraph e of this section. Where underground metallic piping systems are not available, other grounds which provide the desired permanence and conductance may be permitted.

    The 1925 NEC has the grounded conductor (neutral) connected to ground at ONE place - "grounded conductor of an interior wiring system shall have but one grounding connection" (from 902.h.).

    The 1925 NEC also states where that ONE place is to be connected: at the service equipment - "the ground shall be made at each service on the line side of the service switch before the service is connected to the line" (from 902.d.).
    Jerry Peck - CodeMan
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