I have a condition where 500 MCM conductors in a 30" x 24" x 8" NEMA 4X enclosure are tapped with 250 MCM conductors feeding a 125A CB in another 24" x 24" x 8" NEMA 4X enclosure, about 15 feet away. I would like to feed another 125A CB to be installed adjacent to and in the same enclosure from the line side of the first 125A CB. 240.21(B)(5) states it must terminate in a single breaker, which it does - and still will, even if I feed off the line side of that CB via 2-conductor lugs to the second CB. Am I still meeting the spirit of 240.21?
Outside taps of unlimited length
- Thread starter thorpe16
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IMO, yes... but I'm afraid in your case my opinion don't agree with NEC requirements.
Using a 2 conductor lug at the first breaker may be electrically a continuation of the tap conductor, but feeding two breakers with the "same conductor" still means two terminations, two breakers... and not permitted
Using a 2 conductor lug at the first breaker may be electrically a continuation of the tap conductor, but feeding two breakers with the "same conductor" still means two terminations, two breakers... and not permitted
It doesn't matter how you try to explain it, the tap conductor (or set thereof) supplies two overcurrent devices. Under 240.21, any tap conductor supplying more than one overcurrent device is not permitted, with only one exception that I'm aware of: 240.12(C)(3), explicitly regarding transformer secondary conductors of an industrial installation.thorpe16 said:
Otherwise, I agree your proposed installation is safe. Much debate has come about over NEC tap rules. I do not see anything unsafe about multiple overcurrent devices with a summed rating less than the ampacity of the tap conductor. Has it been proposed and rejected? I don't know, as I don't follow the NEC developmental process that close :wink:
Thanks for your input! I don't know if this has been posted to NEC for review, but we'll talk with the AHJ, and if it gets rejected, then we'll just run two taps - each one rated per the 125A load it's feeding. I'll just have to upsize the conductors a smidge to allow for the derating of more than 3 current carrying conductors in a raceway. Thanks again!:grin:
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