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Thread: Table 250.102 (C) (1)

  1. #1
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    Table 250.102 (C) (1)

    Hi all

    Last night, one of my students asked me a question about the above-referenced table in Article 250. He was confused by the boldface heading the right column which reads: Size of Grounded Conductor or Bonding Jumper (AWG or Kcmil). This is followed by an asterisk which sends one to the bottom of the table notes and it reads: For the purposes of this table, the term bonding jumper refers to main bonding jumpers, system bonding jumpers, and supply side bonding jumpers.

    His question was why does it say Grounded Conductor and not just Bonding Jumper. I told him I thought it was because this table refers to supply side conductors and that there are times a utility will size a grounded conductor differently than one might if using article 220. That's just a guess. I promised I would post the question on the forum.

    Anyone care to weigh in?

    Thanks

  2. #2
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    Quote Originally Posted by ohmboyz View Post
    Hi all

    Last night, one of my students asked me a question about the above-referenced table in Article 250. He was confused by the boldface heading the right column which reads: Size of Grounded Conductor or Bonding Jumper (AWG or Kcmil). This is followed by an asterisk which sends one to the bottom of the table notes and it reads: For the purposes of this table, the term bonding jumper refers to main bonding jumpers, system bonding jumpers, and supply side bonding jumpers.

    His question was why does it say Grounded Conductor and not just Bonding Jumper. I told him I thought it was because this table refers to supply side conductors and that there are times a utility will size a grounded conductor differently than one might if using article 220. That's just a guess. I promised I would post the question on the forum.

    Anyone care to weigh in?

    Thanks
    See 250.24(C)(1).

  3. #3
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    Hmmm. Kinda like a circle, no? 250.24 (C) (1) simply refers back to the table I originally asked about. My question is based on an understanding that on the load side, we calculate the size of the grounded conductor according to Article 220. For a single phase delta, it is rare for the grounded conductor to be more than two sizes smaller than the ungrounded ones. In the 250.102 table, the first row would indicate a grounded conductor could be as much as four times smaller than the ungrounded conductor. I'm wondering why this is. I'm wondering why the table doesn't just say in the right hand column, "size of bonding jumper" and simply exclude the term "grounded conductor."

  4. #4
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    Quote Originally Posted by ohmboyz View Post
    Hmmm. Kinda like a circle, no? 250.24 (C) (1) simply refers back to the table I originally asked about. My question is based on an understanding that on the load side, we calculate the size of the grounded conductor according to Article 220. For a single phase delta, it is rare for the grounded conductor to be more than two sizes smaller than the ungrounded ones. In the 250.102 table, the first row would indicate a grounded conductor could be as much as four times smaller than the ungrounded conductor. I'm wondering why this is. I'm wondering why the table doesn't just say in the right hand column, "size of bonding jumper" and simply exclude the term "grounded conductor."
    That table is also used for sizing the minimum size grounded conductor.

    250.24(C) Grounded Conductor Brought to Service Equipment. Where an ac system operating at 1000 volts or less is
    grounded at any point, the grounded conductor(s) shall be routed with the ungrounded conductors to each service dis-
    connecting means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus. A
    main bonding jumper shall connect the grounded conductor(s) to each service disconnecting means enclosure. The
    grounded conductor(s) shall be installed in accordance with 250.24(C)(1) through (C)(4).
    (1) Sizing for a Single Raceway. The grounded conductor
    shall not be smaller than specified in Table 250.102(C)(1).
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  5. #5
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    Quote Originally Posted by ohmboyz View Post
    Hmmm. Kinda like a circle, no? 250.24 (C) (1) simply refers back to the table I originally asked about. My question is based on an understanding that on the load side, we calculate the size of the grounded conductor according to Article 220. For a single phase delta, it is rare for the grounded conductor to be more than two sizes smaller than the ungrounded ones. In the 250.102 table, the first row would indicate a grounded conductor could be as much as four times smaller than the ungrounded conductor. I'm wondering why this is. I'm wondering why the table doesn't just say in the right hand column, "size of bonding jumper" and simply exclude the term "grounded conductor."
    220.61 is for calculating the load of the grounded conductor. The size of the grounded conductor would be the larger size of that required by your load calculation or of that required by table 250.102(C).

  6. #6
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    okey dokey, thanks

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    Quote Originally Posted by packersparky View Post
    220.61 is for calculating the load of the grounded conductor. The size of the grounded conductor would be the larger size of that required by your load calculation or of that required by table 250.102(C).
    +1

  8. #8
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    Quote Originally Posted by ohmboyz View Post
    For a single phase delta . . .
    What is a single phase delta?
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  9. #9
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    Quote Originally Posted by LarryFine View Post
    What is a single phase delta?
    Lonely......
    "Electricity is really just organized lightning." George Carlin


    Derek

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    Quote Originally Posted by LarryFine View Post
    What is a single phase delta?
    Quote Originally Posted by jumper View Post
    Lonely......
    If you go and decide to dance with a gorilla the dance ain't over till the gorilla decides it's over.

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