25 kV Power Cable in Concrete Trench (Grade Raceway)

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sahababu71 Active Contributor Join Date: Feb 2011 Posts: 13	25 kV Power Cable in Concrete Trench (Grade Raceway) 10/19/2014 11:37 PM
	Hi, I have 6(six)- 2 per phase 25 kv 500 mcm XLPE cu power cable which will be routed from 25 kv bus to switchgear building through road crossing heavy duty concrete trench(grade raceway) approximately 55m distance. How I could put my cable? If I put flat formation with 2 layer then what would be the spacing between layers. cable dia 45 mm and what woud be spacing between two cables. Could I put A-B-C from left and on top layer same sequence A-B-C from left. Should I have to calculate any de-rating of ampacity since trench would be be covered.Please advise.
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lyn Guru Join Date: Oct 2008 Posts: 42355 Good Answers: 1693	#1 Re: 25 KV Power cable in concrete trench(Grade raceway) 10/19/2014 11:43 PM
	Where are you? Are you aware of local electrical codes, such as NFPA 70? Maybe you should consider hiring a local electrician?
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TonyS Guru Join Date: Aug 2010 Location: Resting under the Major Oak Posts: 4347 Good Answers: 181	#2 Re: 25 KV Power cable in concrete trench(Grade raceway) 10/20/2014 1:22 AM
	Usual practice is to put the singles in trefoil formation. __________________ The reports of my death are greatly exaggerated.
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sahababu71 Active Contributor Join Date: Feb 2011 Posts: 13	#3 In reply to #2 Re: 25 KV Power cable in concrete trench(Grade raceway) 10/20/2014 1:30 AM
	Thanks a lot. Should I have to do any de-rating calculation? Trefoil would be AA-BB and top CC on top per two cables or ABC ABC two trefoil. For first option is there any spacing requirement between A-A
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TonyS Guru Join Date: Aug 2010 Location: Resting under the Major Oak Posts: 4347 Good Answers: 181	#6 In reply to #3 Re: 25 KV Power cable in concrete trench(Grade raceway) 10/20/2014 7:20 AM
	ABC - ABC There will be a derating factor for which you'll have to refer to your local codes. You don't give the loading so it's hard to say. __________________ The reports of my death are greatly exaggerated.
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chaterpilar Power-User Join Date: Aug 2007 Location: Bhopal India Posts: 234 Good Answers: 5	#4 Re: 25 KV Power cable in concrete trench(Grade raceway) 10/20/2014 1:40 AM
	Lay them in Trefoil formation Each trefoil cable cleats at 1 meter intervals . Ensure at least 350 mm gap between the two Trefoils. See link below for the arrangement. http://www.cablejoints.co.uk/images/gallery/uploads/1380542304_Prysmian%20Dutchclamps%20-%20High%20Voltage%20Trefoil%20Cable%20Cleats.jpg __________________ He must be very ignorant as he answers all the questions he is asked. Voltaire
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sprabakar22 Associate Join Date: Jan 2012 Location: chennai. Posts: 27	#5 Re: 25 KV Power cable in concrete trench(Grade raceway) 10/20/2014 5:52 AM
	Dear Sahababu71, It will be better to refer the standards like IEC 60364, NFPA 70, BS 7671. And as per the site condition. There different type of laying method is there accordingly the de rating factor should be calculated. thanks __________________ Prabakar
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7anoter4 Guru Join Date: Oct 2012 Location: 100 miles North from the World Center Posts: 879 Good Answers: 42	#7 Re: 25 kV Power Cable in Concrete Trench (Grade Raceway) 10/21/2014 4:33 AM
	I am sorry, Pracabar.IEC 60364 it is only for low voltage cable standard. Also NEC [NFPA 70] does not deal with cables in trench- as I know- and BS7671[IEE Wiring Regulation] it is also for low-voltage cables[at a nominal voltage of 230 V a.c. single-phase or 230/400 V a.c. three-phase]. Caterpillar,the way to cleat the single core cables it seems to me correct.Could be the clamps of id-Technik? See: http://www.id-technik.com/de/start/ __________________ Julius
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Anonymous Poster #1	#8 Re: 25 kV Power Cable in Concrete Trench (Grade Raceway) 10/22/2014 9:49 AM
	Useful topic on cable arrangement http://www.psa-outline.com/cable-selection/
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7anoter4 Guru Join Date: Oct 2012 Location: 100 miles North from the World Center Posts: 879 Good Answers: 42	#9 Re: 25 kV Power Cable in Concrete Trench (Grade Raceway) 10/22/2014 12:23 PM
	No standard-as I know-NEC, IEEE, BS [IEE], VDE-which deals with unventilated channels. This book indicates a way to calculate the air temperature rise in such an unventilated channel: Power cables and their application by Lothar Heinhold http://books.google.co.il/books?id=u1sjSgAACAAJ&dq=bibliogroup:%22Power+Cables+and+Insulated+Wires%22&hl=iw&sa=X&ei=U85HVIy0Nand7Qax-4GIDQ&ved=0CBwQ6AEwAA ch.18.5.1 Here attached 4 pages: __________________ Julius
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7anoter4 Guru Join Date: Oct 2012 Location: 100 miles North from the World Center Posts: 879 Good Answers: 42	#10 Re: 25 kV Power Cable in Concrete Trench (Grade Raceway) 10/23/2014 11:17 AM
	It is difficult to see the above image.I'll try to expose only one. __________________ Julius
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7anoter4 Guru Join Date: Oct 2012 Location: 100 miles North from the World Center Posts: 879 Good Answers: 42	#11 Re: 25 kV Power Cable in Concrete Trench (Grade Raceway) 10/25/2014 4:48 AM
	This is the final try: __________________ Julius
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7anoter4 (4); Anonymous Poster (1); chaterpilar (1); lyn (1); sahababu71 (1); sprabakar22 (1); TonyS (2)

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