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Topic Title: old installation cables
Topic Summary: Testing and Inspecting
Created On: 16 May 2013 09:55 PM
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 16 May 2013 09:55 PM
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nige296

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Testing and inspecting an installation tomorrow. On my initial look the conductors on all the cables were not copper but all steel.Just checking if this is any different in the way i record or carry out testing? Thanks
 16 May 2013 10:18 PM
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Legh

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Originally posted by: nige296

Testing and inspecting an installation tomorrow. On my initial look the conductors on all the cables were not copper but all steel.Just checking if this is any different in the way i record or carry out testing? Thanks


I've never come across 'steel' conductors before. What type of installation are you proposing to inspect and test?


Legh

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 16 May 2013 10:33 PM
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michaelbrett

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Are you sure the conductors are not aluminium?

Regards

Mike
 16 May 2013 11:12 PM
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nige296

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sorry, i meant aluminium!!, any difference in domestic testing than copper conductors?
 16 May 2013 11:12 PM
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antric2

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Its possible they may even be the aluminium coated type of stranded conductor used in late 60.s early 70.s and they can be very brittle.

i may be wrong and I will try to source my info,but,I think a recommendation to rewire the property may be the advice I read.I dont know why but I will try to verify.

Regards
Antric
 16 May 2013 11:53 PM
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Legh

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I remember dealing with Aluminium conductors as a youngster when playing around with the house electrics. I remeber that the terminations broke off when I replaced a single for a double socket. Although it was still there when I sold the house 20 years on. I had to google it to remind myself what all the dangers were/are.

They are usually tinned to give a limited amount of protection against electrolytic action when screwed into brass terminals. Small csa's of Aluminum also creeps when screwed down which means it does not make a reliable long term connection. They break easily when terminated - it goes on about the benefits...... and then we got onto the big stuff.

I also remember on holiday in Turkey having a feel of some overhead lines on a cable drum which were in the process of being installed . They were very easy to bend which made me think that they would not make very good transmission lines as they don't support their own weight and it didn't appear to have any steel catenary.

I think if there is an option i would recommend a rewire, as stated above.

Legh

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Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 17 May 2013 10:11 AM
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MrP

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What's your agreed scope?
You don't have to test anything, if that's what you have agreed

MrP
 17 May 2013 11:24 AM
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jcm256

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Old rubber (TRS) 3.029 and 7.029 had shiny conductors VIR had shiny conductors.
Most deterioration on VIR (if it was inside conduit) will be seen where it is exposed to air at distribution boards, sockets, switches etc. Recommend wiring be checked annually to detect further deterioration or recommend rewiring.
 17 May 2013 01:32 PM
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anastasis

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If it is aluminium, I second Legh's comments - the stuff is a disaster. BS7671 prohibits aluminium for anything less than 16mm. I think this ban has been around for a while so I guess they realised it was a bad idea soon after it was introduced. I'd have no hesitation in recommending a full rewire.
 17 May 2013 03:45 PM
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michaelbrett

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Originally posted by: nige296

sorry, i meant aluminium!!, any difference in domestic testing than copper conductors?


Be very careful if you disconnect any cables to carry out tests.

As stated by others, aluminium cables (even the clad stuff) is horribly brittle. If you overtighten when reterminating, you will be in for a real disaster.

For domestic stuff, I seem to remember that rings were wired in 7/036 or 4mm².

For lighting, 3/029 or 1.5mm².

For cookers can't remember what was used. If you need the info, I will need to search through my old stuff in the loft.

Good luck!!

Regards

Mike
 20 May 2013 12:14 PM
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AJJewsbury

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Another possibility if you're not sure is that a lot of pre-metric copper cables were tinned copper - which gave the conductors a silvery appearance rather like aluminium. They were usually stranded though (I think Aluminium was usually solid core?).
- Andy.
 20 May 2013 05:56 PM
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michaelbrett

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Andy

I seem to remember seeing both stranded & solid aluminium cables back in the dim but now very distant past. This is why I detailed both imperial and metric sizes. However, solid was much more common.

However, I could be wrong .

Regards

Mike
 20 May 2013 11:59 PM
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sparkingchip

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A have a sample on the back of my desk from a alteration job. Although I was only working in the kitchen I had to go around the house and tighten virtually every termination at virtually every fitting, once that was done it all tested out fine apart from a higher resistance on the conductors taking Zs close to the limit.

Andy
 21 May 2013 10:52 AM
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tariqahmadani

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You may proceed with the testing in usual way. Cable test is for insulation condition. The result should be same for both AL and CU cables.
 21 May 2013 08:08 PM
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michaelbrett

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Originally posted by: tariqahmadani

You may proceed with the testing in usual way. Cable test is for insulation condition. The result should be same for both AL and CU cables.


Whilst insulation resistance measurements may be similar, you can expect continuity & Zs measurements to be different to an equivalent copper installation.

As previously indicated, extreme care needs to be exhibited if disconnecting & reterminating cables as aluminium conductors are very brittle and tend to deform/ break easily when tightened down.

Regards

Mike
 21 May 2013 08:34 PM
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OMS

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Whilst insulation resistance measurements may be similar, you can expect continuity & Zs measurements to be different to an equivalent copper installation


Is that actually true Mike - the conductivity of aluminium is about 60% that of copper - as such, for the same apacity you have at least a 140% increase in conductor CSA.

for a typical 20A radial circuit wired in 2.5mm2 copper or 4.0mm2 aluminium, I dont think you'd measure much difference in R1 and R2 or Zs

As previously indicated, extreme care needs to be exhibited if disconnecting & reterminating cables as aluminium conductors are very brittle and tend to deform/ break easily when tightened down.


Ain't that the truth

Regards

OMS

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 21 May 2013 09:33 PM
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michaelbrett

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OMS

I have seen many installations in the past where 7/029 or 2.5mm² al cables have been used for ring final circuits. This caused no end of problems that still have not gone away (especially in kitchen circuits and night storage heating (radial) circuits).

It would seem back in 'prehistoric' times, some installers never used larger csa al cables.

I guess I should have stated for the same size csa cables that continuity & Zs would be different (I'm tired after a tough day ).

Back in the day, I can remember a lot of installations being carried out in Al cables around the Sevenoaks areas - I can remember my father & I having to rip a lot of these out in the '80s as there were lots of problem installations around then.

Regards

Mike
 22 May 2013 09:43 AM
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OMS

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Can't disagree with that Mike - I guess if installers were chucking in the equivalent of 7/.029 regardless if it was copper or aluminium, then yes there would be at least 40% difference in the readings.

I know of several housing estates that were done in aluminium T&E - although all power circuits on those were 4.0mm2 - they were a standard Wimpey spec - ring final upstairs with spurs off every socket to downstairs sockets - 20A radial in the kitchen - total disaster - almost every one has been at least partially rewired

regards

OMS

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Failure is always an option
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