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Topic Title: SWA low IR
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Created On: 01 April 2015 06:07 PM
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 01 April 2015 06:07 PM
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12boreblue

Posts: 123
Joined: 29 May 2006

Just tested a system with 30 mtr 4mm 4core SWA IR on red line to E is .35
system is in use for some time with no problems, no trips on rcbo, . Martindale flashes line and e reversed.
voltage varying between poles slightly. Have stripped it down checked for damage etc, can find nothing. Thinking of splitting in the middle testing each end and replacing faulty half. Not easy to access though. Option 2 was to remove any slack and refit each end, in case of damage there, but have checked and found none, all seem ok. Anyone had anything like this and found a solution, or shall I just replace it?Client won't like the cost though!!

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To fail to prepare is to prepare to fail!
 01 April 2015 06:26 PM
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24Hour

Posts: 269
Joined: 06 April 2006

Likely to be water ingress from either damage or a dodgy previous joint reckon, try the insulation tester on 1000v and see if it moves , but do make sure the loads removed first !
A local hire shop to me do a good cable locator that I've found invaluable in the past.

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Yes i do do 24/7 everyday of the FLAMIN year.
 01 April 2015 06:29 PM
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davezawadi

Posts: 3850
Joined: 26 June 2002

Is this 0.35 meg to the armour or another core? If its the armour, you probably have some mechanical damage and water has got between the core and wires, which is usually visible as external damage. I'd change it anyway, cable is not a lot is it? Anyway isolate the cable both ends and measure again, you never know! Check between the armour and earth too, if not high you have got damage somewhere.

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David
BSc CEng MIET
david@ZawadiSoundAndLighting.co.uk
 02 April 2015 09:14 AM
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12boreblue

Posts: 123
Joined: 29 May 2006

Have IR'd every core to every core and earth, @500v only red core to earth at fault, have checked the whole length of cable (it is all above ground) no physical damage.
Will give it another go at 1000v but think it will be a replacement.
Thx guys

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To fail to prepare is to prepare to fail!
 02 April 2015 09:21 AM
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Zoomup

Posts: 3286
Joined: 20 February 2014

I have only ever come across one piece of cable faulty from new, and that was a twin and earth with live to earth shorted. The wholesaler replaced it for nothing, but that did not cover the wasted time and trouble in removing the faulty section and renewing it.

Bye,

Z.
 02 April 2015 09:21 AM
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phantom9

Posts: 1757
Joined: 16 December 2002

What is the red core connected to?
 02 April 2015 11:54 AM
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Zoomup

Posts: 3286
Joined: 20 February 2014

Originally posted by: 12boreblue

Have IR'd every core to every core and earth, @500v only red core to earth at fault, have checked the whole length of cable (it is all above ground) no physical damage.

Will give it another go at 1000v but think it will be a replacement.

Thx guys


Did you insulation resitance test the red core with it totally disconnected at both ends?

Edit, after doing some arithmetic. The insulation resistance of the red to earth is 350 kOhms. The earth leakage will be under 7.0 mA. Not perfect, but there again, not disastrous and not compliant.

Z.

Edited: 02 April 2015 at 12:14 PM by Zoomup
 02 April 2015 03:00 PM
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Legh

Posts: 4029
Joined: 17 December 2004

Are we talking 3ph or single phase.?
I had a similar single phase problem where a 16.0mm2 4-core was used to supply an office and reading room at the end of the garden. The cable was buried under a few tons of soil and rocks.
The red to black conductors were shorting out. The plumbers had done some additional work and had hit the cable, then made a torpedo joint which subsequently failed. I couldn't get to the garden end as its terminations were half buried under a support wall, so made off the joint and ran a separate 3-core cable from the joint to the studio.
Used the Black plus SWA as the cpc and used the blue and yellow as the live conductors.
That was over 2 years ago and is still working.

Legh

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http://www.leghrichardson.co.uk

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