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Old 08-10-2011, 10:57 AM   #1
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Breaker sizing


What does NEC recomend for a breaker rating @480 3phase, feeding a 80kva isolation transformer

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Old 08-10-2011, 11:17 AM   #2
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Would have nothing to do with the NEC, it has to do with manufacturer spec's.

http://www.federalpacific.com/univer.../chapter6.html
http://search.yahoo.com/search;_ylt=...te=&fr2=sp-top

http://www.3phasepower.org/3phasetransformers.htm

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Old 08-10-2011, 11:20 AM   #3
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Quote:
Originally Posted by dale jones
What does NEC recomend for a breaker rating @480 3phase, feeding a 80kva isolation transformer
Hire a licensed electrical contractor. 480 is not s DIY project. Transformers are covered by Article 450 though.
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Old 08-10-2011, 11:22 AM   #4
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Quote:
Originally Posted by gregzoll
Transformers are covered specically on Article 450 of the NEC
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Old 08-10-2011, 11:44 AM   #5
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They may be covered in that article, but it does not change what the manufacturer spec's the equipment out for.
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Old 08-10-2011, 11:51 AM   #6
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Quote:
Originally Posted by gregzoll
They may be covered in that article, but it does not change what the manufacturer spec's the equipment out for.
The OP is asking about sizing the OCPD. Unless his local area does not use the NEC, Article 450 has everything to do with transformers. As does the rest of Chapters 1-4 in general.
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Old 08-10-2011, 11:53 AM   #7
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Instead of citing the NEC, why don't you answer their question for the breaker size, since you are the "expert". Also, not everyone coming on here, especially newbies, know what OCPD stands for.

BTW, I know the answer to the OP question, but do you electures?

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Old 08-10-2011, 01:21 PM   #8
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Breaker sizing


To solve: P / I x E
80 kVA X 1000 = 80000 VA
80000 VA divided by 831 (480 x 1.732) = 96.27 amps
Since the transformer is more than 9 amps you have to use 125 %.
96.27 X 1.25 = 120.34 amps.
Answer: 125 amp cb (the next higher standard, Electrical Code 240-6).
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Old 08-10-2011, 04:57 PM   #9
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Gregzol - where did you get the NEC on your iPhone? There's always an app for that, isn't there?
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Old 08-10-2011, 05:28 PM   #10
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It is the 2008 McGraw Hill version with Iceberg reader. It is around $75. Do a search on the Appstore for "National Electrical". You can also get the app for the Boopsie 2011 NEC changes, and some other stuff. Makes it easy to have on the go.
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Old 08-10-2011, 05:29 PM   #11
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Well if this thread didn't scare off the OP I don't know what will.
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Old 08-10-2011, 05:39 PM   #12
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Well if this thread didn't scare off the OP I don't know what will.
No, I am thinking that the OP was doing homework, and then it went from there.
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Old 08-10-2011, 06:04 PM   #13
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You two bozo's need to learn how to get along. Besides, everyone in the field knows that the correct fuse size is 3/4" copper pipe. Cut to fit.. ;-)~
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Old 08-10-2011, 08:06 PM   #14
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Quote:
Originally Posted by gregzoll
It is the 2008 McGraw Hill version with Iceberg reader. It is around $75. Do a search on the Appstore for "National Electrical". You can also get the app for the Boopsie 2011 NEC changes, and some other stuff. Makes it easy to have on the go.
Phew. Wish I could write that off.
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Old 08-10-2011, 10:16 PM   #15
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Quote:
Originally Posted by Master of Cold View Post
You two bozo's need to learn how to get along. Besides, everyone in the field knows that the correct fuse size is 3/4" copper pipe. Cut to fit.. ;-)~

Is that type L, K, or M copper.

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