Ampacity

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juzdatech Member Join Date: Aug 2010 Posts: 9	Ampacity 08/19/2010 11:01 AM
	With a load rated 460kW, 480v, 3ph., would using (3) 4/0 THHN wires per leg @ aprox. 80' distance, (in conduit) be sufficient w/ a max. 700 amp sorce output? I say yes, some say no. I may be missing a calculation factor. Not sure.
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#1 Re: Ampacity 08/19/2010 12:33 PM
	→ British Standard 7671. _{AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAArgh!} __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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wareagle Guru Join Date: Jun 2008 Location: Alabama Posts: 1604 Good Answers: 63	#2 Re: Ampacity 08/19/2010 1:14 PM
	460 kw/0.48 x 1.730 x 0.79 pf = 700 amps. From table 310.16 NEC 4/0 thhn ampacity = 230 amps x 3 ckts = 690 amps assuming 3 ckts in 3 separate conduits. 4/0 is not large enough. Is this a continuous load(over 3 hrs)? If load is continuous you need to use 700 amps x 1.25 = 875 amps Require 3 ckts of 350 thhn or 4 ckts of 4/0 thhn. Are you using NEC table 310.16 Juzdatech please reply to this post. Table NEC 310.16 http://www.houwire.com/products/technical/article310_16.html
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juzdatech Member Join Date: Aug 2010 Posts: 9	#3 In reply to #2 Re: Ampacity 08/19/2010 1:50 PM
	Thanks wareagle, Yes I was using the same chart, but out of the Uglys Elec. References book (2008). I actually used the 90degC chart @ 260A. I am a tech that was ask my input on this and will not have the final decission. This is an AC Drive feeding a Dyno. The wires actually existed for a 500kW, but was never powered up so it was questionable. It is YTD if it will run continuous or even hit full capacity. Your reply was helpful.
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wareagle Guru Join Date: Jun 2008 Location: Alabama Posts: 1604 Good Answers: 63	#4 Re: Ampacity 08/19/2010 2:52 PM
	You can not use the 90C rating when making this calculation. It is only used when derating the conductor for temp and number of conductors in conduit.
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pnaban Guru Join Date: Jun 2010 Location: srilanka Posts: 2725 Good Answers: 5	#5 Re: Ampacity 08/25/2010 2:41 PM
	Will someone post the document titled"nec conductor sizing.htm" for the benifit all readers?. __________________ pnaban
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juzdatech (1); pnaban (1); PWSlack (1); wareagle (2)

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