The History Of Cable.

[Guest123]

Many thanks to nickblake for originally posting this in a thread.


Paper

• Paper insulation
• From the WW1 era
• Very rare now in domestic wiring
• Paper is somewhat hygroscopic
• Pre-war paper cable is still in service in distribution networks, and causes a good deal of downtime
• The polychlorinated bipehnyl (PCB) used in old paper insulation is toxic, and the insulation should not be handled with bare hands

Lead sheathed

• Common in 1930s for socket circuits
• Used as exterior farm cable well after that
• Lead sheath does not make reliable earth connections
• Rubber inner insulation
• Tail rubber insulation tends to disintegrate, and muck accumulates on cable ends causing leakage

VIR

• Vulcanised India Rubber insulated cable.
• Along with imperial T&E, one of the most common historic wiring cables still in use
• Comes in 2 forms:
  • Twisted pair, cotton/rubber insulated, with no outer sheath
  • singles drawn into conduit
• Most VIR wiring doesn't include an earth wire, which is sometimes run as a separate uninsulated single.
• Rated to 60C
• Rubber insulation perishes, cracks & falls off
• Properties with VIR cable are usually in urgent need of rewiring, and may represent a significant safety risk. However some of the Jute / Hessian reinforced rubber cables that are often seen on consumer unit incomers are still often relatively safe.

A good percentage of the remaining old VIR wiring is now in a dangerous condition, especially at termination points. It is common to see insulation that has fallen off, often leaving live & neutral conductors bare, unsupported and in very close proximity. In the worst cases 2 bare conductors can be found twisted round each other with nothing rigid to support them.
The outer insulation has failed on the black sheath of the cable, and in one place the insulation on the inner live wire has also cracked off. This cable is in a very poor state, and is unsafe.

The rule of thumb with old rubber wiring is

• replace it as soon as possible
• don't move it at all, even small movement sometimes causes shorts.

This situation is quite different to early American rubber wiring, which is usually still in sound condition, due to the use of a different rubber formulation.



TRS

• Tough Rubber Sheath
• Rubber insulated conductors with a rubber outer sheath

CTS

• Cab Tyre Sheathed
• Tinned copper conductors, each core insulated with VIR, & cab tyre outer sheath
• Single, Flat Twin and Flat Triple
• (I'm not familiar with this one, but presumably it looks like TRS)

Aluminium

• Cheaper alternative to copper
• Used from 1950s to 1970s, and old stock sometimes used into the 1980s.
• The insulation & sheathing is mostly the same as T&E - PVC for decades, may be rubber on older cable.
• A known fire risk
• Aluminium cable creeps, oxidises & fractures, all of which can cause fires.
• Requires special connections, do not connect to old ali cable using connectors intended for copper.
• Al requires a larger conductor size than Cu for the same current rating
• Presence of aluminium cable may be considered a material fact for insurance.
• The main problem with ali cable is its thermal expansion coefficient. Repeated temperature cycling causes it to come loose at connection points, and it then oxidises, and aluminium oxide is an insulator. Bad connections generate excessive heat and fire can break out.

Copper Clad Aluminium

• Each conductor has an aluminium core surrounded by copper
• An attempt to improve the properties of ali cable
• Significantly better than al, the surface oxidation problem is eliminated, creep reduced & the risk from cracking more or less eliminated

PBJ

• PolyButyl Jute insulated cable
• Rubberised Hessian appearance to the sheath.
• The surface is these cables is quite uneven
• Commonly used for mains incomer insulation
• Lots of old PBJ is still safely in service

Imperial T&E


PVC twin



Older T&E wiring having similar construction to today's cables. Several versions exist:

• 7/.029 T&E
  • imperial 7 stranded version of 2.5mm² T&E
  • used for socket circuits until unstranded 2.5mm T&E was introduced around 1970
  • strands are 0.029" diameter = 0.74mm
• 3/.029 T&E
  • imperial 3 stranded version of 1mm² T&E
  • used for lighting circuits
  • 1/.044" unstranded lighting cable also used
• Ashathene T&E
  • Precursor to PVC T&E
  • Lasts well
• PVC outer VIR inner
  • an early T&E cable
  • where the inner rubber has failed, the tails can be sleeved
• 2 core Twin
  • no earth, used for lighting circuits, or power circuits with a separate (usually uninsulated) single run alongside to provide an earth.

PVC and ashathene versions of this cable last well and are usually in good condition, but rubber does not last well long term.
PVC outer rubber inner cable can have its rubber ends sleeved to make it safe, as its only the ends where exposed to air where the rubber becomes brittle and falls off. Cable with rubber outer insulation can not be made safe this way.
​

 

[Spudnik]

Good post Lenny/Nick.

 

[Burnt Fingers]

I had some lead sheathed on a job - someone had used as a dropwire on POTS. Fascinating - thanks

 

[rocker]

Good post... dunno if DIY Wiki would be happy with it's use without a direct link though....

 

[nickblake]

and guess what i came across last week original braided paper insulated cable from 1930's and guess what its still in use , cant do anything about it till the guys out of hospital bike crash , the elderly lady who lives in the house with the son has lost the plot , all she talks about is the war , so sad when i get in to do it ill gets some pics so watch this space

 

[Graeme Harrold]

Good post... dunno if DIY Wiki would be happy with it's use without a direct link though....

Spookily I just posted the Wiki link in another thread............

 

[Pip]

Lenny, great post, just one question, VIR cable = rewire ASAP, (my neighbours house has this. Frightening) TRS cable, does this also require a rewire?

Have a friend who needs a new CU in a bungalow, and they mentioned a rewire, but on inspection the cable looks fine. They don't want to spend money if not needed

I have read other post's and some say rewire, others say if it test OK leave it alone.
Your views please

 

[Graeme Harrold]

Personally Id always advise a re-wire. Given the age of these installations, the vulcanised rubber will either have failed or will be failing, a quick inspection will normally locate crumbling coatings.

 

[nickblake]

i know its over a week ago but im going to agree with graeme on this one VIR rubber needs rewiring as soon as possible as the rubber can disintegrate rapidly even if it does look in good condition ,easier to rewire than rebuild

 

[PC Electrics]

I've created my own imperial cable rating guide which I use when changing CUs. I attach it here for you all to use.

 

[Knobhead]

Here’s one I hope I never come across
View attachment 7001

 

[Guest123]

Nice to see that one Tony.....do you have any others???

 

[Knobhead]

Laying cables in Mansfield 1910, PILC in brick ducts which were then filled with pitch. These were 650V DC for the tram system.

View attachment 7003

 

[Knobhead]

As an apprentice I worked on a 2.5KV system that had 600V grade VIR laid in a wooden duct with hard wood cleats separating the cores. The whole duct was then filled with pitch. It was installed during WW2 it was still live and in use in the late 70’s. It was a bodge and codge job due to the war, but it kept on working so why mess about with it?

 

[Knobhead]

Couldn’t see it getting past the 17[SUP]th[/SUP]