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prems4573 Participant Join Date: Oct 2009 Posts: 4	Exact Derating Factor 04/19/2011 5:08 AM
	What is the exact derating factor to be considered for selecting the rating of a breaker for a capacitor in an APFC Panel? __________________ Prem
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electricalexpert65 Guru Join Date: Oct 2009 Posts: 2061 Good Answers: 169	#1 Re: Exact Derating Factor 04/19/2011 6:47 AM
	Why to de-rate in the first place? The only thing to check is the inrush current of the last capacitor in a bank with all other capacitors already ON and check whether the making capacity of the breaker is more than this worst case scenario inrush current. Also, to be checked is the setting (both current as well as time) in the Instantaneous and/or Short Time Releases of the breaker. And, ensuer that the release wouldn't trip for a switching inrush.
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Tornado Guru Join Date: May 2009 Location: Richland, WA, USA Posts: 21017 Good Answers: 795	#2 Re: Exact Derating Factor 04/19/2011 8:00 AM
	The word "exact" is fishy. __________________ In vino veritas; in cervisia carmen; in aqua E. coli.
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kvsridhar Guru Join Date: Sep 2009 Location: Temporarily at Ashburn, VA Posts: 2744 Good Answers: 164	#3 Re: Exact Derating Factor 04/19/2011 8:51 AM
	In addition to the good points by ee65, may i add: 1. Thermal derating factor of 1.43 as explained by AEG here.. 2. Circuit breakers should be used for protection only. Capacitor switching should be done by contactors specially designed for this purpose. If CB is used for switching on and off, its life will be over very soon. Contactors have a life of millions of operations while CBs have a life in thousands only. __________________ Nothing worthwhile can ever be taught, it can only be learnt.
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wareagle Guru Join Date: Jun 2008 Location: Alabama Posts: 1604 Good Answers: 63	#4 Re: Exact Derating Factor 04/19/2011 1:53 PM
	NEC requires the breaker to be 135% of the capacitor amperage.
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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	#5 Re: Exact Derating Factor 04/19/2011 3:17 PM
	What about looking in British Standard 7671? __________________ "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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Users who posted comments:

electricalexpert65 (1); kvsridhar (1); PWSlack (1); Tornado (1); wareagle (1)

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