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Thread: #2 SER on a 100 amp breaker

  1. #1

    #2 SER on a 100 amp breaker

    I have seen numerous times a 2224 ser cable used with a 100 amp breaker. But when you look up 2224 ser in 310.16, allowable ampacity is only 90 amps......i was under the impression that if used for a subpanel, it was allowed to be on a 100 amp breaker..... i have searched the code and cant find the exception anywhere....Any insight?

  2. #2
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    You are correct, #2 Aluminum SER cable is rated at 90 amps per Table 310.16 on the 75 degree column. So you can't install a larger breaker than a 90 amp breaker on this cable to a sub-panel.

    What I have seen is that people are mis-applying Table 310.15(B)(6). They are using this table for a feeder from a panel to another panel.

    I hear alot of people that call Table 310.15(B)(6) the "Residential Table" and think it applys to all residental feeders.

    Chris

  3. #3
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    Under the 2008 code cycle SER used as feeders or branch circuits must be sized from the 60 degree column.

    338.10 Uses Permitted.
    (B) Branch Circuits or Feeders.
    (4) Installation Methods for Branch Circuits and Feeders.
    (a) Interior Installations. In addition to the provisions of this article, Type SE service-entrance cable used for interior wiring shall comply with the installation requirements of Part II of Article 334.

    334.80 Ampacity.
    The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60°C (140°F) conductor temperature rating. The 90°C (194°F) rating shall be permitted to be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60°C (140°F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.11.

    Now that 2-2-2-4 is only good for 75 amps
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    Mike Whitt
    God answers Knee-Mail.

  4. #4
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    Agreed, The 2008 has really changed the way we will install SER cable for interior wiring.

    Chris

  5. #5
    yes that must be were i was screwed up, its no wonder i couldnt find a code section permitting 100a breaker on 2 ser and now 75 amps.......... i cant even tell you times i have seen this install or seen my previous employer premorm it.............

  6. #6
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    Quote Originally Posted by scottdbutcher View Post
    yes that must be were i was screwed up, its no wonder i couldnt find a code section permitting 100a breaker on 2 ser and now 75 amps.......... i cant even tell you times i have seen this install or seen my previous employer premorm it.............
    Agree, I see this violation quite often.

    Chris

  7. #7
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    As seen in another thread, inspectors don't get it either.
    There are two kinds of people - those smart enough to know they don’t know, and those dumb enough to insist they do.-----Margery Eagan

    Open shop since 1988

  8. #8
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    Quote Originally Posted by electricmanscott View Post
    As seen in another thread, inspectors don't get it either.
    Agreed.

    Chris

  9. #9
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    Quote Originally Posted by electricmanscott View Post
    As seen in another thread, inspectors don't get it either.
    They don't?:smile:

  10. #10
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    New Mexico
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    We use 2224 AL ser about twice a week to feed panels off of the meter base on a 100a brkr. No inspector ever says anything.

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