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Thread: When to apply the 120% rule for bus rating.

  1. #1
    Join Date
    Sep 2014
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    dallas tx
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    When to apply the 120% rule for bus rating.

    If I have a 200 amp main breaker panel and I line side tap the service conductors to a 60 amp disconnect that's 50 amp fused ( for a PV system)do I need to apply the 120% or does that only apply if I back feed the disconnect.


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  2. #2
    Join Date
    May 2011
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    3,687
    The reason to do a line side connection is to avoid any of the load side rules including the 120% rule. Also under the 2014 code and later the 120% rule only applies to panelboard busbars and not to conductors, disconnects, or anything else.

  3. #3
    Join Date
    Sep 2014
    Location
    dallas tx
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    That's what I thought. Although we failed an inspection. The AHJ said the panel was too small for the PV system.
    I think he may have thought it was back fed.


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