Cable fault identification

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rajakumar1985 Participant Join Date: Jun 2011 Posts: 2	Cable fault identification 06/29/2011 8:22 AM
	One 3.5C cable is connected in a feeder with the neutral is isolated in the two ends(3 phases connected and neutral open in both sides). Now on rear end the output voltage is getting reduced by 20V in two phases and 40v increased by another phase.(between phase and neutral but neutral in open in two ends).the cable is meggered and we got the value of 100Mega ohm. There is no load in rear end. Kindly clarify
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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: Cable fault identification 06/29/2011 8:32 AM
	Hang on - the voltage relative to what, please? __________________ "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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North of 60 Guru Join Date: Mar 2007 Location: Iqaluit, NU. Canada Posts: 1854 Good Answers: 140	#2 Re: Cable fault identification 06/29/2011 9:07 AM
	More then likely... You are reading the voltage potential, by going from a phase conductor to the disconnected neutral, created by capacitive coupling between the phase and neutral conductors. What does the neutral show relative to ground? I would bet you will see a voltage there as well, only that would be because of inductive coupling. You can ignore this condition. __________________ Joe Contractor to Electrical Inspector, "What do you mean you are going to make me follow the code?".
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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	#3 In reply to #2 Re: Cable fault identification 06/29/2011 9:11 AM
	Quite. __________________ "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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Ayyavaru Active Contributor Join Date: Sep 2010 Location: Hyderabad Posts: 11 Good Answers: 1	#4 Re: Cable fault identification 06/30/2011 7:30 AM
	No problem connect some minimum load at rear end and check the voltage it will be O.K. After test reply back for further clarification. __________________ "Everything you can imagine is real." -- Pablo Picasso
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harry potter Power-User Join Date: Nov 2008 Location: India Posts: 333 Good Answers: 6	#5 Re: Cable fault identification 06/30/2011 8:54 AM
	1. This happens due to un balancing of voltages / load with floating star neutral. This is exactly similar to star connected lamps feeded with 3 phase, & common point of lamps keeping floating, while switching on, during transient, one of the lamp will blow. This is due to floating - oscillating neutral, creating un balancing of voltages near load side, even though, incoming voltage is balanced. __________________ Exploring the Science of Electricity
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