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Thread: Duplex service conductor

  1. #1
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    Duplex service conductor

    Based on 2014:

    I was reviewing my code book and got to thinking about duplex service conductors and I did my own practice load calcs and here is what I came up with.

    1.Unit A & B each calculated load is 67A and 62A
    2.Minimum service rating for each is 100Amps based on 230.79(C)
    3.Single overhead riser conduit with single set service conductors is based on 129 amps
    4.Based 310.15(b)(16) my over head service conductors are based on the calculated load of both units 129 amps = #1 copper conductors

    Am I correct?

    Or size of the service conductors is based on the main over current protection times two (so 200Amp and use 3/0)

    Thank you
    Edward
    Education is a progressive discovery of our ignorance.


  2. #2
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    If 310.15(16) applies you are correct.

    But 310.15(16) is for not more then 3 current carrying conductors in raceway cable or earth with ambient temp of 30C.

    conductors in free air get to use a different table, which one applies to your conductors?

    Quite often this is POCO's service drop cable and they don't have to comply with NEC either. Many of them around here would drop a #2 aluminum to this service.

  3. #3
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    Quote Originally Posted by kwired View Post
    If 310.15(16) applies you are correct.

    But 310.15(16) is for not more then 3 current carrying conductors in raceway cable or earth with ambient temp of 30C.

    conductors in free air get to use a different table, which one applies to your conductors?

    Quite often this is POCO's service drop cable and they don't have to comply with NEC either. Many of them around here would drop a #2 aluminum to this service.

    The service conductors in my question is not the service drop. I know the service drop is under the POCO jurisdiction. The 3 CCC does not apply because I have two hots and one neutral in the service riser conduit.
    Edward
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    Quote Originally Posted by edward View Post
    The 3 CCC does not apply because I have two hots and one neutral in the service riser conduit.
    You are looking at that aspect the wrong way, it says "not more then" 3 current carrying conductors, but still if they are in free air another table may apply and actually allow for higher ampacity from same conductors.

    Are you selecting size of the "overhead" conductors that are in free air or are you selecting size of the conductors in the riser conduit? Maybe I misunderstanding what you were asking about?

  5. #5
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    Quote Originally Posted by kwired View Post
    ...
    Are you selecting size of the "overhead" conductors that are in free air or are you selecting size of the conductors in the riser conduit? Maybe I misunderstanding what you were asking about?
    #3 in OP. The conductors will not be in free air.
    Quote Originally Posted by edward View Post
    3.Single overhead riser conduit with single set service conductors is based on 129 amps
    I'll never get there. No matter where I go, I'm always here.

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    Quote Originally Posted by edward View Post
    The service conductors in my question...
    You did not post your load calculation. For combined service entrance conductors you may be able to take advantage of 75% demand for four or more fixed-in-place appliances if the individual units could not.

    Is this new construction? ...one meter or two? If one meter I have to question here whether or not the duplex units can legally be under one meter and billed as one service by the power company.

    You will not be able to take advantage of 310.15(B)(7) the way it is worded.
    I'll never get there. No matter where I go, I'm always here.

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    Quote Originally Posted by kwired View Post
    You are looking at that aspect the wrong way, it says "not more then" 3 current carrying conductors, but still if they are in free air another table may apply and actually allow for higher ampacity from same conductors.

    Are you selecting size of the "overhead" conductors that are in free air or are you selecting size of the conductors in the riser conduit? Maybe I misunderstanding what you were asking about?
    Which aspect I have the wrong way?
    Edward
    Education is a progressive discovery of our ignorance.


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    Edward, to answer your question the risers can be based on the calculated load however if you want to leave room for growth then you may want to up the size of those conductors

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    Quote Originally Posted by Dennis Alwon View Post
    Edward, to answer your question the risers can be based on the calculated load however if you want to leave room for growth then you may want to up the size of those conductors

    That is all i wanted to learn if in this case the service conductors are based on calculated load or based on the main OCPD.
    Edward
    Education is a progressive discovery of our ignorance.


  10. #10
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    Quote Originally Posted by edward View Post
    That is all i wanted to learn if in this case the service conductors are based on calculated load or based on the main OCPD.
    The minimum is based on the calculated load. However, service ocpd rating has a mutual relationship with the service conductor ampacity... and vice versa.
    Last edited by Smart $; 04-22-17 at 10:00 AM.
    I'll never get there. No matter where I go, I'm always here.

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