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Thread: Bonding Jumper supply side

  1. #1
    Join Date
    Jan 2009
    Location
    Williamsburg,VA
    Posts
    112

    Bonding Jumper supply side

    Good afternoon fellow professionals. We have an 800 amp service . Leaving the CT are 3 (parallel) sets of (4) 400MCM aluminum conductors in metal raceway. We need to bond these raceways. Based on 250.102 ( C) (1) our inspector says we can use a 1/0 copper. I dont agree. The chart says " Size of ungrounded conductor OR equivalent area for parallel conductors." Based on this, I dont use the largest ungrounded conductor to size this, I use the area of the ungrounded conductors since we are in parallel. By doing this, I exceed the chart (over 1750 kcmil because I have 9 ungrounded 400's which equal 3600 kcmil) The notes below the chart tell me I cannot be less than 12.5% of the equivalent area of ungrounded conductors but do not have to be larger than the largest ungrounded conductor. I calculate I need a 400kcmil as a bonding jumper for these raceways entering my service disconnect.

    GO!!

  2. #2
    Join Date
    May 2011
    Posts
    3,687
    See 250.102 (C)(2). I think the inspector is right, if there are separate raceways and bonding jumpers.

  3. #3
    Join Date
    Sep 2016
    Location
    Longmont, CO
    Posts
    146
    I believe you only have to add up the conductors in one raceway or cable, not all the ungrounded conductors.

    (2) Size for Parallel Conductor Installations in Two or More
    Raceways or Cables. Where the ungrounded supply conductors
    are paralleled in two or more raceways or cables, and an individual
    supply-side bonding jumper is used for bonding these raceways
    or cables, the size of the supply-side bonding jumper for each
    raceway or cable shall be selected from Table 250.102(C)(1)
    based on the size of the ungrounded supply conductors in each
    raceway or cable. A single supply-side bonding jumper installed
    for bonding two or more raceways or cables shall be sized in
    accordance with 250.102(C)(1).

    I agree with the inspector as well.

  4. #4
    Join Date
    Jan 2009
    Location
    Williamsburg,VA
    Posts
    112
    Thanks guys. I have a hard time with this because table 250.102 ( C ) ( 1) doesn't state per conduit. It states the equivalent conductors of the paralled conductors which is 3600 total kcmil.

  5. #5
    Join Date
    Sep 2016
    Location
    Longmont, CO
    Posts
    146
    By definition, all the ungrounded conductors are not paralleled, only the ungrounded conductors of one phase or leg of the system. So, you would multiply 3 times 400 MCM, and have an equivalent of 1200 MCM aluminum, which looks like it would require a 2/0 copper.

  6. #6
    Join Date
    Jun 2006
    Location
    Ohio
    Posts
    21,042
    (C) Size β€” Supply-Side Bonding Jumper.

    (1) Size for Supply Conductors in a Single Raceway or

    Cable. The supply-side bonding jumper shall not be
    smaller than specified in Table 250.102(C)(1).

    (2) Size for Parallel Conductor Installations in Two or
    More Raceways. Where the ungrounded supply conductors
    are paralleled in two or more raceways or cables, and
    an individual supply-side bonding jumper is used for bonding
    these raceways or cables, the size of the supply-side
    bonding jumper for each raceway or cable shall be selected
    from Table 250.102(C)(1) based on the size of the ungrounded
    supply conductors in each raceway or cable. A
    single supply-side bonding jumper installed for bonding
    two or more raceways or cables shall be sized in accordance
    with 250.102(C)(1).
    You have to size per (C)(1) or (C)(2). The latter permits you to run a smaller individual BJ to each raceway. If you run one BJ to all raceways, you must size per the former.

    3 sets of 400kcmil Al in 3 conduits

    #2 Cu or 1/0 Al to each raceway
    β€”orβ€”
    2/0 Cu or 4/0 Al to all three raceways
    I will have achieved my life's goal if I die with a smile on my face.

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