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Topic Title: Rubber cable
Topic Summary: IR Readings
Created On: 05 April 2014 10:57 PM
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 05 April 2014 10:57 PM
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SKElectrical

Posts: 910
Joined: 01 February 2009

Hi all, I surveyed a property today, 50% of elec wiring was rubber sheathed t+e.
Am I right in saying that this was last installed circa 1955?

The IR readings varied but I saw 50 Meg Ohm crop up a bit. Is this a typical reading for rubber t+e?
 05 April 2014 11:04 PM
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hifly

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my parents council house built in 1956 was rubber cabling, apart from where the cable had been exposed to heat at light fittings it was in very good condition when i rewired it in 2006.

At light fittings all the rubber had crumbled and just left bare conductors.

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 05 April 2014 11:53 PM
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sparkingchip

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I tested some a few weeks ago and the insulation had fell off in places exposing the copper conductors to touch.

I still achieved over 20 Mohms as an insulation test result, so don't put too much faith in your insulation test results!

Andy
 06 April 2014 06:35 AM
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normcall

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Our 'affluent' society is the problem.
Who would have thought the masses could afford >40w light bulbs and central heating?
It's the extra heat that dries out the oil in the rubber so it has nothing to bind it together.

-------------------------
Norman
 06 April 2014 06:42 AM
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GeoffBlackwell

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This reminds me of a story from my shady past that says something about the value of testing.

In the early seventies my partner in crime and I rewired 350 local authority house in Ramsgate Kent. When the contract ended we were looking for more work and we were invited to quote for a similar contract in Ashford Kent. The reason I mention all of this is just to show that we knew a bit about house bashing .

We duly quoted what we thought was a competitive price - to arrive at this price we had visited some sample houses so we knew that they were wired in rubber. We opened a ceiling rose and noted that the rubber was very dry.

The upshot is we did not get the job - when we asked for feedback we were told that the council architect had commissioned some testing and he decided that all the houses needed were a few additional circuits and a complete renewal of all fittings. He based all this on insulation resistance test results only - no inspection.

Some years later I applied for a job in the Architects department in Ashford. He interviewed me but he had no idea that I had quoted for work there in the past.

He started the conversation by telling me that all electrical contractors were crooks . It transpired that work on the houses had started but it soon ran into trouble because many terminations fell apart as they tried to replace the fittings on the old rubber cable. They had to revert to complete rewires at a far higher costs than we had quoted.

We did not get on so I never got the job - probably a lucky escape .

So inspect the rubber carefully - don't just rely on test results. Make sure you have the means with you to effect repairs as the rubber insulation might fail when handled.

Regards

Geoff Blackwell

Edited: 06 April 2014 at 07:10 AM by GeoffBlackwell
 06 April 2014 07:37 AM
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sparkingchip

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"Make sure you have the means with you to effect repairs as the rubber insulation might fail when handled. "

A roll of black tape colour matches the cable, but using a nice bright yellow tape highlights the problems
 06 April 2014 09:01 AM
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alanblaby

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I did one last year, 2 circuits in rubber (VIR).
Insulation readings were excellent - >200Mohms.
However, wherever the rubber was exposed,at the accessories, it was crumbing away. The houseowner would not pay for a rewire, so I sleeved it as best as possible, and noted the faults, and highlighted on the Cert that it should be inspected every year, or preferably rewired ASAP.

I wasnt called back to Inspect it this year.
 06 April 2014 09:24 AM
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Jaymack

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Originally posted by: GeoffBlackwell
So inspect the rubber carefully - don't just rely on test results. Make sure you have the means with you to effect repairs as the rubber insulation might fail when handled.

I would advocate just condemning it and not removing any accessories at all, especially those subject to higher current loadings. l removed a socket for inspection one time; the insulation crumbled away for about 100mm at the terminals leaving bare copper. I replaced the socket gingerly, leaving no DNA at the scene!

Rubber cable, a la TRS and CTS, was a hazard in industry when subject to oil around hydraulic systems; it softened, was easily torn, and became swollen to two or three times it's original diameter.

Regards
 06 April 2014 09:44 AM
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GeoffBlackwell

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I would advocate just condemning it and not removing any accessories at all, especially those subject to higher current loadings.


You won't get many rewires like that Jaymack - you need to show the client the terrible truth .

Another story from my shady past places us on the S.S Benloyal - somewhere in the Indian Ocean in 1970. I was the 2nd Electrical Officer - the ship was wired with VIR cables.

I had to replace some lamps in an engine room indicator panel. When I opened it up I saw that the single cables to each lamp had been neatly coiled. I also saw that all of the insulation had fallen off - but no shorts had occurred - not what you would expect in the engine room of a ship as there is a fair amount of vibration.

Regards

Geoff Blackwell

Edited: 06 April 2014 at 11:03 AM by GeoffBlackwell
 06 April 2014 12:08 PM
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Grobbyman

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Hello Geoff.
My father was a chippy with Ben line.
Perhaps you met him, George Robertson.
Regards
George
 06 April 2014 01:33 PM
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GeoffBlackwell

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It's possible but it was a long time ago .

Regards

Geoff Blackwell
 06 April 2014 09:13 PM
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SKElectrical

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Thanks for replies. Rewire ahoy.
 06 April 2014 09:30 PM
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phantom9

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Whenever I see VIR in a property I put the tester away and say "rewire". Like has been demonstrated on this thread, VIR can pass insulation testing but when you see large chunks of it crumbling away from the conductors in the loft and under the floor you know it needs replacing. I am surprised there is any left! Anyone still finding lead sheathed?
 06 April 2014 10:02 PM
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mikejumper

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I suppose all an insulation test tells us is that there is sufficient distance beween the conductors and that there isn't dampness in an enclosure somewhere.
 07 April 2014 10:09 AM
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BigRed

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Yep, agree, rewire. Cost me a sunday afternoon at a mates with the only place to get electrical stuff being wicks... cost me mate a nice bottle of makers mark too. This stuff is geting way beyond its sell by date, and really the only recourse is a rewire. I've found this with PVC twin , no earth too. Power in VR, lights in twin PVC( and sticky as hell)
 07 April 2014 11:36 AM
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potential

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When I first started in the 60s I came across a lot of rubber cable.
In nearly every instance it was damaged near heat or where there was arcing (ozone) such as switches or poor connections.
Mind you I also came across early PVC that had gone terribly wrong too and it was relatively new at that time.
The bad batch/run of PVC/PVC was available/installed about 59-60 ish.
The problem was with the inner PVC sheaths where there was a termination that had a bend in the cable associated with it.
(i.e. virtually every single one)
The sheath would split off the copper core completely and straighten leaving the core completely bare.
This happened wherever the faulty cable had been used and the outer sheath had been cut back.
The red sheath was more prone to do it than the black.
When you opened the cover of a fusebox (as they were called then) you might find it filled with long bare, bright tinned, live curly copper wires coming out of the fuse carriers.
Not nice to find particularly if working in a dark damp cellar and the fusebox was all metal.
 07 April 2014 11:49 AM
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OMS

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Originally posted by: phantom9

Whenever I see VIR in a property I put the tester away and say "rewire". Like has been demonstrated on this thread, VIR can pass insulation testing but when you see large chunks of it crumbling away from the conductors in the loft and under the floor you know it needs replacing. I am surprised there is any left! Anyone still finding lead sheathed?


Could we conclude that VRI cabling, is, in your opinion, potentially dangerous then Phantom ? given the outcome of your risk assessment being "to rewire"-

I know of a few lead sheathed installations, still going strong (but under enhanced inspection regimes).

At a bigger scale, there is still a lot of PILC about as well

Regards

OMS

-------------------------
Failure is always an option
 07 April 2014 11:53 AM
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geov

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Originally posted by: phantom9

Whenever I see VIR in a property I put the tester away and say "rewire". Like has been demonstrated on this thread, VIR can pass insulation testing but when you see large chunks of it crumbling away from the conductors in the loft and under the floor you know it needs replacing. I am surprised there is any left! Anyone still finding lead sheathed?


Only last week I got an early evening call from my mother's neighbours, husband & wife in their late 70's. Something had gone bang. To cut a long story short, their 1930's semi was 85% wired in lead sheathed, with only an attic extension in t&e. I'm down for the rewire, but the house is stacked to the rafters with a lifetime's possessions - I'm trying to persuade them to go to their son's house for a week!
 07 April 2014 12:34 PM
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phantom9

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Originally posted by: OMS

Originally posted by: phantom9



Whenever I see VIR in a property I put the tester away and say "rewire". Like has been demonstrated on this thread, VIR can pass insulation testing but when you see large chunks of it crumbling away from the conductors in the loft and under the floor you know it needs replacing. I am surprised there is any left! Anyone still finding lead sheathed? [IMG][/IMG]




Could we conclude that VRI cabling, is, in your opinion, potentially dangerous then Phantom ? given the outcome of your risk assessment being "to rewire"- [IMG]/forums/forum/i/expressions/face-icon-small-wink.gif" border="0[/IMG]

I know of a few lead sheathed installations, still going strong (but under enhanced inspection regimes).

At a bigger scale, there is still a lot of PILC about as well

Regards

OMS


I think an improvement in this term would be the same as that used in some of the Guidance Notes. I quite like the term "danger present" as used in GN3. It brings an urgency to the situation, whereas, the wishy-washy undefined "potentially" dangerous says nothing other than "well, it might be dangerous but then again it might not". Atrocious terminology to be used in a technical document. I will keep pushing this until someone listens, OMS.
 07 April 2014 12:36 PM
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phantom9

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Do you know how PILC cable fails? Just interested because I don't know.
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