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Topic Title: Replacement of older cables
Topic Summary: Regualtions pertaining to replacement of older cables
Created On: 10 November 2007 06:59 PM
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 10 November 2007 06:59 PM
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pradeep_pk

Posts: 27
Joined: 18 April 2002

Is there any regulatory requirement of replacing older cables (say more than 25 years old) with new cables? If the insulation value is OK, can we maintain the same old cable?
 10 November 2007 07:32 PM
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michaelbrett

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Are they PVC/PVC or VRI?
 10 November 2007 07:42 PM
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daveparry1

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Joined: 04 July 2007

VRI needs to be replaced but PVC/PVC is ok provided ins resistance is good.
regards.
 11 November 2007 07:02 AM
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normcall

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Joined: 15 January 2005

Perhaps you would be kind enough to point me in the direction of the regulation that says rubber cables need to be replaced regardless.

-------------------------
Norman
 11 November 2007 08:41 AM
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ebee

Posts: 6570
Joined: 02 December 2004

Well said Norm lad

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 11 November 2007 09:04 AM
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michaelbrett

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Originally posted by: normcall

Perhaps you would be kind enough to point me in the direction of the regulation that says rubber cables need to be replaced regardless.


Norman

I know I'm asking for trouble, but, here goes.

Had the OP replied, I would have asked if the PVC/PVC was exuding green gunge. If not leave alone (assuming insulation resistance is okay).

The accepted lifetime of VRI cables is 25 years. Now from what I understand VRI cable was used in the 1950s. So that makes 50 years. So, if the rubber is brittle & dropping off the cable (especially points of interconnection) it should be replaced. Also you cannot see under floors through walls as to what might be happening.

With regard to regulations ( Iknow you were probably asking daveparry1), I would say that external influences sec 522 would probably apply. I still have a roll each of lead cable & VRI that are perfectly okay - so I can see where you are coming from.

Look forward to your comments.

Regards

Mike

Edited: 11 November 2007 at 09:05 AM by michaelbrett
 11 November 2007 09:43 AM
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Jaymack

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This is what the said document states on the subject: -

Part P approved document Appendix C

Tough Rubber Sheathed (TRS), vulcanized rubber insulated (VRI) cables
Prior to the use of pvc insulated cables becoming common in the 1960s, most cables installed in domestic dwellings were of the rubber insulated, tough-rubber sheathed (TRS) type. These are easily recognizable by their black exterior.
The extent to which the insulation and sheath deteriorate in service depends very much on whether the cable has been subjected to overloading and/or excessive temperature, or the rubber has been exposed to direct sunlight. Deterioration results in a loss of insulating properties, with the rubber becoming dry and inflexible, perhaps with a tendency to crumble.
Such wiring installations should be tested by a competent person at the earliest opportunity, but otherwise left undisturbed until replacement, as they are beyond their normally expected safe working life.

Lead sheathed cables
Lead sheathed cables may be found in some installations dating from before about 1948. These have rubber insulated, tinned copper conductors and an outer sheath of lead.
For reasons of protection against indirect contact (electric shock) it is essential that the lead sheath of every such cable is, and will remain, properly earthed.
The conductor insulation, being made of rubber, is prone to deterioration as described above for TRS cables.
Again, such wiring installations should be tested by a competent person at the earliest opportunity as they are beyond their normally expected safe working life.

No change then unless.....

If doing an installation, I would be wary of disturbing existing VIR cables, particularly at DB's and accessories where the hardening of the rubber is usually more pronounced, in my experience, due to the heat sink properties of the cables/terminations. I foolishly unscrewed and pulled out a SSO one time, while inspecting to give a quotation for minor job. The VIR insulation fell off, now I had to "patch" the insulation, (I declined to quote). Be afraid.....very, very afraid of this stuff - Needless to say I recommended a rewire.
Now I check at the DB to check whether VIR is present; and act accordingly depending on the work requested.
There is always a possibility, that there is a problem with the insulation - hardening/embrittlement, where the cables are not exposed (hidden from view). If any new work is carried out and there is a problem, if these cables are disturbed. Even if the work involved was not directly relevant, there would always be the suspicion that you caused any problem.

Jaymack
 11 November 2007 10:21 AM
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daveparry1

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Hi Norman, I know theres no reg to say that VIR or TRS has to be replaced but whenever I see any of it these days, (usually part of an old installation that`s been disconnected) the rubber is always in a very poor state.
regards,
Dave.
 11 November 2007 10:42 AM
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normcall

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Heat is the problem with the old rubber cables and I can assure you that installations without central heating last a lot longer.
Being fair, most properties have some form of heating and this dries the oil out and thus the cables get brittle.

Once again, you have to judge every installation on what is found on inspection, rather than what the book says.
As I think I've mentioned before, I recently declined to quote for a rewire because the 'NICEIC' approved inspector who carried out a PIR said the property needed rewiring as it didn't comply with the current BS7671 - it was only rewired the the mid 1970's.
After I pointed out that yet another rewire will be required next year on that basis, I saved the church some £3000 by just doing remedials.

-------------------------
Norman
 11 November 2007 10:47 AM
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potential

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Vulcanized rubber insulated (VRI) cables were alway vulnerable to heat damage and exposure to the sun.
A brand new cable would deteriorate in a matter of months under those conditions.
Also wherever ozone was created, (sparking switches, motor brushgear, fuses etc) resulted it the rubber petrifying eventually turning to dust.
Similarly, oil would dissolve the insulation.

However let's not forget that rubber insulated cable in good safe conditions is a much superior insulator when compared to PVC, which is relatively poor to most other forms of cable insulation, paper and pressurized oil being the best.
 11 November 2007 10:50 AM
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briggsy6

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This is what BASEC have to say about rubber insulated cable.

http://www.basec.org.uk/news/b...ews-detail.asp?news=8
 11 November 2007 11:38 AM
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potential

Posts: 1732
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Originally posted by: briggsy6
This is what BASEC have to say about rubber insulated cable.
http://www.basec.org.uk/news/b...tail.asp?news=8

An interesting link but I wonder how much of it is based on fact?
For instance, and I quote:
Last year, there were more than 40,000 incidents of house fires recorded in England alone.

Is it being suggested that the fires were all caused by VRI cable? (or at all?)
 11 November 2007 12:20 PM
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Jaymack

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Originally posted by: potential

However let's not forget that rubber insulated cable in good safe conditions is a much superior insulator when compared to PVC, which is relatively poor to most other forms of cable insulation, paper and pressurized oil being the best.


Even when new, care had to be exercised with installing VIR single core cable, in that it had a waxy fabric braiding material as a "sheath" cover. I expect this was to improve the mechanical properties - e.g. abrasion at the installation time.
This had to be cut back from the rubber by about 10mm to achieve good insulation results at the termination ends, probably because this was hygroscopic. If the rubber crumbles inside this sheath, this braiding will "fall" onto the bare conductor reducing the cable insulating prooerties.

Jaymack
 11 November 2007 12:26 PM
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flameport

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Joined: 28 January 2007

Originally posted by: potential

Is it being suggested that the fires were all caused by VRI cable? (or at all?)


The article certainly implies this - why include the figure otherwise.
The actual number is more like 2000 fires caused by electrical wiring.
 11 November 2007 02:23 PM
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pradeep_pk

Posts: 27
Joined: 18 April 2002

They are XLPE insulated PVC sheathed underground power cables
 11 November 2007 03:05 PM
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normcall

Posts: 8541
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I would like you to take a deep breath and imagine how many of these cables the electricity suppliers have installed and try to recall how many have been replaced because they are 25 years old. The joints generally expire before the insulation.

-------------------------
Norman
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