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Thread: Wire sizing for 100% Rated Breakers

  1. #11
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    more detail

    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?

  2. #12
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    Quote Originally Posted by Matt Donovan View Post
    ...
    Does that clear it up?
    Yes. Thank you.

    Hmmm.... this is a tough one. You'd be good on the PV side of the 3000A 100% breaker. Don't forget the new section for it must also be listed for the use of 100%-rated breaker(s). The question is whether the 100% rating can be applied to the service side... and I simply cannot say yes with no reservations. I'm leaning towards no because there is no exception in Article 230 for 100%-rated breakers like there is in Articles 210 and 215. Yet it seems stupid if you can run 8 sets of 500mcm on the PV side and not be able to on the service side. If I were you I'd be contacting my AHJ on this one and present the argument I just stated (which assumes the service conductors are 90°C-rated copper conductors).
    I will have achieved my life's goal if I die with a smile on my face.

  3. #13
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    Quote Originally Posted by Matt Donovan View Post
    ..I'd like to not upgrade those.
    Prove original service conductors were installed with <= 3 CCC's per conduit, and perhaps a few ºC below ambient conditions (underground Duct Bank), and 230.42(A)(2) may avoid service-conductor upgrades.
    Roger Ramjet NoFixNoPay

  4. #14
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    Quote Originally Posted by ramsy View Post
    Prove original service conductors were installed with <= 3 CCC's per conduit, and perhaps a few ºC below ambient conditions (underground Duct Bank), and 230.42(A)(2) may avoid service-conductor upgrades.
    Aha! I was going to say that doesn't get around 230.42(A)(1) but I just did a reread and noticed the general statement says (1) or (2)... or (3) if 2014... and there it is....
    (3) 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
    I was thinking that section said all numbered conditions must be met like 210.19 and 215.2... but it does not.

    Under 2017, that was moved to 230.41(A)(1) Exception No. 2. Probably done just to make it consistent with 210.19 and 215.2.
    Last edited by Smart $; 08-11-17 at 09:07 PM.
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  5. #15
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    Sorry, should clarify 2017 NFPA-70 230.42(A)(2)
    Roger Ramjet NoFixNoPay

  6. #16
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    Quote Originally Posted by Matt Donovan View Post
    Here's the situation:

    I have a continuous load that draws 2800A. Normally, I would size the circuit for 1.25 x 2800A = 3500A. But if I use a 100% rated breaker sized at 3000A, does the wire still need to be sized for 1.25x2800A = 3500A? Or will a 3000A feeder still work? (8) sets of 500mcm CU are existing, and I'd like to not upgrade those.
    240.4(C) Overcurrent Devices Rated over 800 Amperes. Where the overcurrent device is rated over 800 amperes,
    the ampacity of the conductors it protects shall be equal to
    or greater than the rating of the overcurrent device defined
    in 240.6.

  7. #17
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    NEC 2017 215.2(A)(1)(a) allows feeder conductors to be sized using the 90 degree column, as long as the terminals at each end are rated at 90 degrees. If terminated in a panelboard, the C/B must be rated at 100% (not 80%). It also permits feeder sizing at 100% of the continuous load (not 125%) and 100% of the non-continuous load.

  8. #18
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    Quote Originally Posted by Unbridled View Post
    NEC 2017 215.2(A)(1)(a) allows feeder conductors to be sized using the 90 degree column, as long as the terminals at each end are rated at 90 degrees. If terminated in a panelboard, the C/B must be rated at 100% (not 80%). It also permits feeder sizing at 100% of the continuous load (not 125%) and 100% of the non-continuous load.
    100%-rated breakers are still 75*C equipment. To be utilized at the 100% rating, 90*C-rated conductors are required, but you still have to use 75*C for termination temperature limits.
    I will have achieved my life's goal if I die with a smile on my face.

  9. #19
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    Quote Originally Posted by Smart $ View Post
    100%-rated breakers are still 75*C equipment. To be utilized at the 100% rating, 90*C-rated conductors are required, but you still have to use 75*C for termination temperature limits.
    You are correct Smart. My interpretation is that you can install 90 degree lugs on a C/B, and pull 90 degree conductors, however i,f the entire assembly is not rated at 90 degree, then you must work with 75 Degree ampacity of the conductors.
    One option the poster has is to install two enclosures with termination blocks. One close to his switch board and also one near his sub panels. He can Install Feeder conductors from the switchboard to the enclosure with terminal blocks and work with 75 degree ampacities ( short Distance). Then he can continue his feeder from the load side of the 90 degree rated terminal block in this enclosure to the 2nd enclosure with 90 degree conductors and Terminations, using 90 degree ampacities. then continue up to his sub-panel with 75 degree ampacities.

    Why? He can save an enormous amount of money using a 90 degree rated conductors for his feeders between enclosures, rather than 75 degree.

    Just a thought.

  10. #20
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    Quote Originally Posted by Unbridled View Post
    ...
    One option the poster has is to install two enclosures with termination blocks. One close to his switch board and also one near his sub panels. He can Install Feeder conductors from the switchboard to the enclosure with terminal blocks and work with 75 degree ampacities ( short Distance). Then he can continue his feeder from the load side of the 90 degree rated terminal block in this enclosure to the 2nd enclosure with 90 degree conductors and Terminations, using 90 degree ampacities. then continue up to his sub-panel with 75 degree ampacities.

    Why? He can save an enormous amount of money using a 90 degree rated conductors for his feeders between enclosures, rather than 75 degree.

    Just a thought.
    While true, I do not see how this relates to the situation presented.
    I will have achieved my life's goal if I die with a smile on my face.

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