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Thread: Grounded Conductor Brought to Service Equipment

  1. #1
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    Exclamation Grounded Conductor Brought to Service Equipment

    The 2008 NEC, Article 250.24(C) states:
    " Where an ac system operating at less than 1000 volts is grounded at any point, the grounded conductor(s) shall be run (i.e. from the utility point of service) to each service disconnect means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus..........."

    Is there any reference in the NEC to systems at, or at greater than 1000 volts requiring a grounded conductor(s) when in similar conditions as in the above article?. I have not been able to find any reference.
    In is my opinion for the conditions in Article 250.24(C),the need for a low impedance path to the utility source is needed.

  2. #2
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    Generally the NEC speaks of "600 volts or less" and "Over 600 volts". For article 250 they only appear to deal with up to 1000 volts.

    Could it be that utilities don't deliver more than a 1000 volts and anything higher than that is on the utility side-- which is not governed by the NEC?????

    I am sure there is a better answer than this one.

  3. #3
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    Article 250 Part X deals with 1KV & over. Basically these systems must comply with Article 250 plus specific rules in Part X.

    The building where I work has 12000 volts coming from the POCO into our switchgear.

  4. #4
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    Angry Grounded Conductor Brought to Service Equipment

    Thank you for the responses to date, and i am attempting to clarify my original question.
    Should the service conductors, for a 4,160Y/2,400v service, from the service panel(s) to a utility point of service include a grounded conductor ?
    Assume the conditions in Article 250.24(C) under which a grounded conductor is required exists.

    It appears to me that the reasons requiring the grounded conductor for a grounded AC system should be the same regardless if is operating at less, equal or over 600 volts. But that is just my opinion............
    Anybody has better arguments?

  5. #5
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    Part of the problem with an answer is that a medium voltage system can be grounded in many different ways or be ungrounded. This depends upon how important continunity of service is to the customer. The other problem is the POCO does not fall under the NEC.

    If the system is supposed to be solidly grounded I would full expect to see a grounded conductor pulled in with the ungrounded conductors, unless no line to neutral loads are served. In that case the steel conduit ( wiring method ) may be supplying the low impedance path back to the service.

    Am I hitting nearer to the mark ??

  6. #6
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    I am not sure why 250.24(C) is limited to 1000 volts and less as it appears to me that 250.24(A) requires this for any premises wiring system that is supplied from a grounded AC service.
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  7. #7
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    Grounded or grounding conductor? Unless you are counting concentric neutral on a MV cable, I have never seen a grounded conductor in MV. Of course I have not seen all the possible applications.:-?

  8. #8
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    I see neutral bus in switchgear a few times each year with a system or main bonding jumper. I never get to see the other end of the connection.

  9. #9
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    Quote Originally Posted by Ed Infante View Post
    ... Is there any reference in the NEC to systems at, or at greater than 1000 volts requiring a grounded conductor(s) when in similar conditions as in the above article?. I have not been able to find any reference.
    In is my opinion for the conditions in Article 250.24(C),the need for a low impedance path to the utility source is needed.
    References are 2005:
    First look at 250.20.C. That says that 1kv and over you can either ground or not -no restrictions.

    If the system is grounded, then as SG mentioned, go to Sec X. Specifically read 250.184.B and C. The only place the code specifically requires a neutral is mentioned in 250.184.B.6.

    I think that the code panel is tellng us that they are not going to cookbook design systems 1kv and up. One is actually going to have to understand the systems and design accordingly. If so, this is one thing that code panel 5 got right. (Yes, there are several others)

    cf

  10. #10
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    Quote Originally Posted by Ed Infante View Post
    ...Should the service conductors, for a 4,160Y/2,400v service, from the service panel(s) to a utility point of service include a grounded conductor ?
    Assume the conditions in Article 250.24(C) under which a grounded conductor is required exists.

    It appears to me that the reasons requiring the grounded conductor for a grounded AC system should be the same regardless if is operating at less, equal or over 600 volts. But that is just my opinion............
    Anybody has better arguments?
    Well, with no N-G loads, and single point grounded, there is no need for a neutral. There must be an equipment grounding conductor and that will be connected to the neutral back at the xfm.

    So, my answer is: It depends

    As for, "the reasons requiring the grounded conductor for a grounded AC system should be the same regardless if is operating at less, equal or over 600 volts." I agree. However under 1kv, the code requires cookie cutter design, regardless of the physics, science, or system requirements. 1kv and up, the code recognizes that cookie cutter design is impractical.

    cf

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