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Thread: Been a while since I

  1. #1
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    Been a while since I

    I am looking at building a 600 amp service (re-doing a 600 amp delta service). The utility company wants to do away with the delta service that is existing.
    The existing service (as I was told) runs from overhead to underground into the building in 6" PVC with aluminum conductors.
    I am to install a disconnect on the utility new utility pole. The current service does not have the proper number of conductors in the existing conduit, therefore copper wire will be required.
    The service has been there for quite some time [concerned about removing the existing wires from approximately 80 feet of underground PVC].
    I am currently figuring on whether runs of 2,000 kcmil THWN copper or paralleling 400 THWN copper as per cost, handling the size of the wires, & what will fit in the conduit.
    As per table 250.66, it appears that 3/0 copper grounding (ground to us old timers) conductor will be adequate in either case (since over 1100 kcmil copper will be used)? BUT then per table 250.122, it appears that #1 copper (since 600 amp disconnect) ?
    And then Table 250.102(C)(1) Grounded conductor (neutral) 12 1/2% of the area of the largest ungrounded conductor. 12.5% x 2,000 kcmil = 250 copper ?
    Thanks for you'll input.

  2. #2
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    IMO forget about 2000 kcmil, if you think that pulling out the old conductors might be a problem try pulling in that stuff.

    If you're using one raceway with parallel conductors then you have to consider derating for more than 3 CCC's in a raceway. So to look at some possible variations you want to get 600 amps in a single 6" PVC conduit?
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  3. #3
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    Quote Originally Posted by infinity View Post
    IMO forget about 2000 kcmil, if you think that pulling out the old conductors might be a problem try pulling in that stuff.

    If you're using one raceway with parallel conductors then you have to consider derating for more than 3 CCC's in a raceway. So to look at some possible variations you want to get 600 amps in a single 6" PVC conduit?
    One of my concerns was, if I had the right tables and looked at them right about the sizing of the conductors for the grounded & grounding (neutral & ground) for the 600 amp service. I wanted to verify this before I started calculating the fill for the 6" PVC. I see that I had already messed up and had used 80% instead of the 70%.
    I was looking at paralleling 400 THHW to get the 600 amps.
    500 kcmil from 90 degree col. 430 amp
    7 - 9 conductors 70% 430 x 70% = 301 amps

  4. #4
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    A few things, your neutral probably doesn't count as a CCC so you can use the 80% derating factor. There is no EGC since you're on the line side of the service disconnect so forget T250.122. If you have no neutral load then the minimum size neutral can be sized according to T250.102(C).
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  5. #5
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    Quote Originally Posted by infinity View Post
    A few things, your neutral probably doesn't count as a CCC so you can use the 80% derating factor. There is no EGC since you're on the line side of the service disconnect so forget T250.122. If you have no neutral load then the minimum size neutral can be sized according to T250.102(C).
    What I was told by the owners, is that the utility company wants a disconnect on their pole, before the underground pull to the inside of the building. Thanks

  6. #6
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    Quote Originally Posted by JDB3 View Post
    What I was told by the owners, is that the utility company wants a disconnect on their pole, before the underground pull to the inside of the building. Thanks
    If the disconnect that POCO wants installed on their pole is just a disconnect, with no fuses or circuit breakers, it does not satisfy the NEC definition of a service disconnect and so the conductors downstream of that disconnect would still be service conductors under the NEC. If a fused disconnect controlled by the customer is present, it is hard to argue that it is not the service disconnect, making the downstream run a feeder requiring separate neutral and EGC (although a raceway EGC may still be used).

  7. #7
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    Quote Originally Posted by GoldDigger View Post
    If the disconnect that POCO wants installed on their pole is just a disconnect, with no fuses or circuit breakers, it does not satisfy the NEC definition of a service disconnect and so the conductors downstream of that disconnect would still be service conductors under the NEC. If a fused disconnect controlled by the customer is present, it is hard to argue that it is not the service disconnect, making the downstream run a feeder requiring separate neutral and EGC (although a raceway EGC may still be used).
    I will be getting with the utility engineer myself later, but I am fairly certain that they & the city will want fused disconnect at the utility pole before it changes to underground. Thanks

  8. #8
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    As per table 250.66, it appears that 3/0 copper grounding (ground to us old timers) conductor will be adequate in either case (since over 1100 kcmil copper will be used)? BUT then per table 250.122, it appears that #1 copper (since 600 amp disconnect) ?

    Any advice on the sizing of the grounding conductor ?

  9. #9
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    Quote Originally Posted by infinity View Post
    A few things, your neutral probably doesn't count as a CCC so you can use the 80% derating factor. There is no EGC since you're on the line side of the service disconnect so forget T250.122. If you have no neutral load then the minimum size neutral can be sized according to T250.102(C).
    If there is a fused disconnect on the pole, before the wires go underground to the inside of the building, "would a grounding conductor be required" ?

    OR

    If the wires feed underground into a fused disconnect outside of the building, "would a grounding conductor be required" ?

    The above questions according to the 2017 NEC.
    A B I G thanks!

  10. #10
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    Quote Originally Posted by JDB3 View Post

    1)If there is a fused disconnect on the pole, before the wires go underground to the inside of the building, "would a grounding conductor be required" ?

    OR

    2)If the wires feed underground into a fused disconnect outside of the building, "would a grounding conductor be required" ?

    The above questions according to the 2017 NEC.
    A B I G thanks!
    1) Yes, that would be a feeder.

    2) Service conductors do not have an EGC.
    "Electricity is really just organized lightning." George Carlin


    Derek

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