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Thread: HVAC Disconnect sizing

  1. #21
    Join Date
    Feb 2003
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    Connecticut
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    Quote Originally Posted by hhsting View Post
    So MCA > BCSC > Rated load current. Whats the harm in using MCA as HVAC disconnect current rating?
    For a combination load piece of equipment, the required disconnect size could be larger than the MCA.

  2. #22
    Join Date
    Jul 2005
    Location
    LA basin, CA
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    Quote Originally Posted by packersparky View Post
    It doesn't. It says the disconnecting means shall be at least 115 percent of the nameplate rated-load current or branch circuitselection current, whichever is greater..
    My local IAEI CEU classes are training inspectors Nameplates always override code, per NEC 110.3(B). Perhaps streamlining complexity for combo. inspectors, not expected to master all code yet.

    Nevertheless, our inspectors are running around enforcing Nameplate, and being told to red tag anyone who tries to quote Code, especially if they've been doing it that way for years.

    Quote Originally Posted by hhsting View Post
    So MCA > BCSC > Rated load current. Whats the harm in using MCA as HVAC disconnect current rating?
    If the inspector is enforcing nameplate, and believes MAX FUSE describes disconnect requirements, it is best to error on the side of caution.
    Roger Ramjet NoFixNoPay

  3. #23
    Join Date
    Dec 2011
    Location
    Wisconsin
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    447
    Quote Originally Posted by ramsy View Post
    My local IAEI CEU classes are training inspectors Nameplates always override code, per NEC 110.3(B). Perhaps streamlining complexity for combo. inspectors, not expected to master all code yet.

    Nevertheless, our inspectors are running around enforcing Nameplate, and being told to red tag anyone who tries to quote Code, especially if they've been doing it that way for years.

    If the inspector is enforcing nameplate, and believes MAX FUSE describes disconnect requirements, it is best to error on the side of caution.
    An inspector should be enforcing the nameplate values for MOCP and MCA, but the nameplate will not tell you what size disconnect to use. For that we have to use 440.12

  4. #24
    Join Date
    Jun 2018
    Location
    Glen bunie, md, us
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    64
    Quote Originally Posted by packersparky View Post
    An inspector should be enforcing the nameplate values for MOCP and MCA, but the nameplate will not tell you what size disconnect to use. For that we have to use 440.12
    So would nec 440 apply to roof top units (RTU) where they have indoor unit and outdoor unit split system with condensing unit outdoor?

    Sent from my SM-G935U using Tapatalk

  5. #25
    Join Date
    Dec 2007
    Location
    NE Nebraska
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    37,928
    Quote Originally Posted by hhsting View Post
    So would nec 440 apply to roof top units (RTU) where they have indoor unit and outdoor unit split system with condensing unit outdoor?

    Sent from my SM-G935U using Tapatalk
    Read 440.1. Split systems usually have a hermetic compressor in the outdoor unit. If there is no hermetic compressor 440 doesn't apply.

    422 applies to the indoor unit with no hermetic compressor.
    I live for today, I'm just a day behind.

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