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Thread: Ground Sizing 250.122

  1. #11
    Join Date
    Feb 2003
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    Illinois
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    Quote Originally Posted by jumper View Post
    ...
    I am pretty sure the 2017 now allows parallel multi-conductor cables with a standard sized EGC to be used in raceways if a full sized EGC is installed also and all the EGCs are tied together.
    Just to be clear, that would only apply where all of the sets of cables are in a single raceway. Not likely for the application in this thread. It also works for all of the sets in a single cable tray and that would be more likely for this application.
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

  2. #12
    Join Date
    Aug 2016
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    Canada
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    So if the cable tray meets 392.60(B), I'd be allowed to use the tray as a EGC ? Does that means the AIA cables wouldn't be required to have a ground in it ?

    I thought there was some rules when you used cable tray like the ones for ampacity like for a 1200A you need a 3/0 or a parallel #2 or something like that.

    Anyway, thanks for all the answers

  3. #13
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    Nov 2010
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    Fort Collins, Colorado
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    Quote Originally Posted by davidb123 View Post
    So if the cable tray meets 392.60(B), I'd be allowed to use the tray as a EGC ? Does that means the AIA cables wouldn't be required to have a ground in it ?

    I thought there was some rules when you used cable tray like the ones for ampacity like for a 1200A you need a 3/0 or a parallel #2 or something like that.

    Anyway, thanks for all the answers
    Assuming your tray meets 392.60(B), 250.122(F)(2)(c) would allow you to forgo the separate EGC. Article 250.122(F)(2)(b) would still require "normal" sized EGCs to be present in the cable and used as well.
    Hope you noted the previous comment that your 500's won't be large enough in most cases as they are only good for 380 amps @ 75 degree. Of course, there are some applications where this would be OK @ the 90 degree rating, but that is another subject.

  4. #14
    Join Date
    Apr 2009
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    Williamsburg, VA
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    Quote Originally Posted by don_resqcapt19 View Post
    You can't use 3 sets of 500 kcmil for a 1200 amp circuit no matter how you install it.
    This.

    240.4 (C) would prohibit using three sets of 500 MCM for a 1200 amp breaker. 380a @75*C x 3 = 1140A. You would need 3 sets of 600 MCM, or, as I just mentioned in another thread, use Polaris connectors, which are rated at 90* C, at each end of the 500 MCM run, then use short pieces of 600 MCM from those connectors to the MCC and breaker terminals, which are rated 75*C.
    Electricians do it until it Hertz!

  5. #15
    Join Date
    Aug 2016
    Location
    Canada
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    14
    240.90(B) allow me to use 3 x 500MCM for a 1200A breaker since I meet requirement for a supervised industrial installation. The real problem is the gnd size that comes with the 500MCM since is a #2AWG and 250.122 requires a 3/0 in each cable...

    Thanks guys

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