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Topic Title: Cable Capacitance Testing
Topic Summary: Cable Testing
Created On: 07 December 2012 03:17 PM
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 07 December 2012 03:17 PM
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ridd9056

Posts: 3
Joined: 05 October 2011

Cable Capacitance Test
650V IT Distribution System

Can anyone advise on a correct method for this test.
 07 December 2012 06:49 PM
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Avatar for rocknroll.
rocknroll

Posts: 8837
Joined: 03 October 2005

I presume from your post this is a medical location???, cable capacitance testing is unfortunately a very inaccurate science even under laboratory conditions, the equipment you need for this is a capacitance bridge that is capable of measuring within 0.01% of absolute value, my advice would be to run this through the cable manufacturer first as they might have values available, you can get capacitance meters and they tend to be rack mounted and expensive.

regards

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"Take nothing but a picture,
leave nothing but footprints!"
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"Oh! The drama of it all."
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"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
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Edited: 10 December 2012 at 12:45 AM by rocknroll
 07 December 2012 07:16 PM
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OMS

Posts: 19593
Joined: 23 March 2004

I doubt it's medical Rock - not at that voltage

MEiGan doesn't call up capacitive testing as the limit if for 10kVA per system so capacitive coupling will be low.

650V, ITearthed sounds industrial to me - you need knowledge of the cable capacitance because you don't have solid earthing (it will influence the earth fault current)

Regards

OMS

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Failure is always an option
 09 December 2012 10:53 PM
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paulskyrme

Posts: 769
Joined: 12 February 2003

I'd guess @ 650V it would be railway related?...
 09 December 2012 11:56 PM
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alancapon

Posts: 5760
Joined: 27 December 2005

I believe the London Underground traction supply is a 630v dc IT system with earth monitoring. In some stations, the lift and escalator supplies are taken from the traction supply.

Regards,

Alan.
 10 December 2012 12:19 PM
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Inrush

Posts: 703
Joined: 19 December 2007

Judging by the voltage I would guess this is probably a non-earth referenced Network Rail signalling feeder.

you need knowledge of the cable capacitance because you don't have solid earthing (it will influence the earth fault current)


Yes, I would think the OP is trying to determine the touch voltage under 1st earth fault conditions.

Edited: 10 December 2012 at 12:48 PM by Inrush
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