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Thread: Wire sizing for 100% Rated Breakers

  1. #21
    Join Date
    Apr 2016
    Location
    Tampa, Fl
    Posts
    140
    Quote Originally Posted by Matt Donovan View Post
    The existing service is metered at the transformer, it has 8-sets underground landing in a two-section switchboard. The left section is a termination and pull section, the right section has up to 6 service disconnects sized 400A to 1200A each (there is no 3000A main existing). I would tap into that left section, and install a new section to the far left with a 3000A breaker for solar. Thats the 100% rated breaker we're talking about. The existing service conductors are the ones I am concerned about.

    Does that clear it up?
    I'm trying to figure why you are concerned about your existing service conductor ratings. Are you at any time going to be utilizing your existing service conductors for feeding power back to the utility as in an interactive PV system?
    Obviously, your existing service conductors are size to handle your existing load. Adding a PV inter-connection doesn't increase your load on the SE Lateral.
    As long as your PV system has been sized properly and does not exceed the Buss rating of your switchboard, I don't see the effect on your existing SE.
    Is your Switchboard rated at 100%? or just the Breaker?

    Please reply

  2. #22
    Join Date
    Oct 2009
    Location
    Austin, TX, USA
    Posts
    8,456
    Pardon my naivete, but how can whether the breaker is 100% rated or not affect the conductor ampacity needed to service the load?

  3. #23
    Join Date
    Apr 2016
    Location
    Tampa, Fl
    Posts
    140
    Quote Originally Posted by ggunn View Post
    Pardon my naivete, but how can whether the breaker is 100% rated or not affect the conductor ampacity needed to service the load?
    SERVICE ENTRANCE CONDUCTORS

    230.42 (A)(3) Minimum Size and Rating.
    The sum of the noncontinuous load plus the continuous
    load if the service-entrance conductors terminate in an
    overcurrent device where both the overcurrent device
    and its assembly are listed for operation at 100 percent
    of their rating

    Otherwise:
    230.42(A)(1) The sum of the noncontinuous loads plus 125 percent
    of continuous loads

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