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  1. #1
    Jerome W. Young's Avatar
    Jerome W. Young Guest

    Default service entry cable sizing

    House had a 225 amp SqD breaker with

    [aluminum] 4/0 awg 600v rhh or rhw service

    The breaker itself indicated the following: #4-300mcm cu/al.

    I believe 4/0 can carry 200 amp max?

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  2. #2
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    Default Re: service entry cable sizing

    Correct. #4/0 AWG aluminum is rated for 200 amps.

    The rating on the breaker is for the approved conductor sizes allowed in the terminals.

    I'm sure you got the multiple tapped neutrals. For all those empty terminals, why on earth did they put 2 and 3 in the same terminal? Then the grounds too.

    Last edited by Jerry Peck; 01-16-2009 at 07:29 AM. Reason: correcting a typo Jeff pointed out - correcting #4 AWG to #4/0 AWG
    Jerry Peck, Construction / Litigation Consultant
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  3. #3
    Jerome W. Young's Avatar
    Jerome W. Young Guest

    Default Re: service entry cable sizing

    aren't they allowed 2 per terminal? three i know is wrong.


  4. #4
    Kevin Barre's Avatar
    Kevin Barre Guest

    Default Re: service entry cable sizing

    Quote Originally Posted by Jerome W. Young View Post
    aren't they allowed 2 per terminal? three i know is wrong.
    Only one per terminal for neutrals. Typically two per terminal for the grounds -- IF they are the same gauge and material and meet size requirements. Read the paper instructions in the panel to let you know what this mfr allows.

    Last edited by Kevin Barre; 01-15-2009 at 07:35 PM.

  5. #5
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    Default Re: service entry cable sizing

    Quote Originally Posted by Kevin Barre View Post
    Only one per terminal for neutrals. Typically two per terminal for the grounds -- IF they are the same gauge and material and meet size requirements. Read the paper instructions in the panel to let you know what this mfr allows.
    Plus, neutrals and grounds not allowed in same terminal. In same terminal bar, yes (if service equipment) ... in same terminal, no.

    Jerry Peck, Construction / Litigation Consultant
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  6. #6
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    Default Re: service entry cable sizing

    Quote Originally Posted by Jerry Peck View Post
    Correct. #4 AWG aluminum is rated for 200 amps.

    The rating on the breaker is for the approved conductor sizes allowed in the terminals.

    I'm sure you got the multiple tapped neutrals. For all those empty terminals, why on earth did they put 2 and 3 in the same terminal? Then the grounds too.
    Apparently Jerry, you've never seen a lazy sub contractor's effort ... :-)

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  7. #7
    Jeff Remas's Avatar
    Jeff Remas Guest

    Default Re: service entry cable sizing

    Quote Originally Posted by Jerry Peck View Post
    Correct. #4 AWG aluminum is rated for 200 amps.

    The rating on the breaker is for the approved conductor sizes allowed in the terminals.

    I'm sure you got the multiple tapped neutrals. For all those empty terminals, why on earth did they put 2 and 3 in the same terminal? Then the grounds too.
    Do you mean 4/0 aluminum?


  8. #8
    Jeff Remas's Avatar
    Jeff Remas Guest

    Default Re: service entry cable sizing

    Rhw can only handle 190A
    Rhh can only handle 205A

    If it is rated for both then the higher of the two applies.


  9. #9
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    Default Re: service entry cable sizing

    Quote Originally Posted by Jeff Remas View Post
    Do you mean 4/0 aluminum?
    Yes, thanks, I went back and corrected it.

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  10. #10
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    Default Re: service entry cable sizing

    Quote Originally Posted by Jeff Remas View Post
    Rhw can only handle 190A
    Rhh can only handle 205A
    Jeff,

    See: (underlining is mine)
    - Table 310.15(B)(6) Conductor Types and Sizes for 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. Conductor Types RHH, RHW, RHW-2, THHN, THHW, THW, THW-2, THWN, THWN-2, XHHW, XHHW-2, SE, USE, USE-2
    - - 4/0 aluminum - 200 amp (reading through the table from right under Aluminum to the left under Rating)

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  11. #11
    Jeff Remas's Avatar
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    Default Re: service entry cable sizing

    Yes, I understand that but the cable is already rated at 205 so the 200A allowable ampacity for 4/0 aluminum in single family residences is not relevant since they used a higher rated conductor.


  12. #12
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    Default Re: service entry cable sizing

    Quote Originally Posted by Jeff Remas View Post
    so the 200A allowable ampacity for 4/0 aluminum in single family residences is not relevant since they used a higher rated conductor.
    That is still relevant as those are the allowable ratings for those conductors in dwelling unit service and feeder use.

    Jerry Peck, Construction / Litigation Consultant
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  13. #13
    Wayne Price's Avatar
    Wayne Price Guest

    Default Re: service entry cable sizing

    According to the California code, based on the NEC, 4/0 copper can handle 250 amps, while 4/0 aluminum or copper-clad aluminum will conduct 200 amps safely.


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