Historic Mains Cables

Before the 1960s several types of cable were used at various times.

Paper

• Paper insulation
• From the WW1 era
• Very rare now

PBJ

• PolyButyl Jute insulated cable
• Rubberised Hessian appearance to the sheath.
• Commonly used for mains incomer insulation,
• Lots of old PBJ is still safely in service

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

VIR

• Vulcanised India Rubber insulated cable.
• The most common historic wiring
• Comes in 2 forms:
  • Two layers of rubber insulation, one on each conductor, and an overall sheath.
  • Twisted pair, cotton/rubber insulated, with no outer sheath
• Both types usually don't include an earth wire, which is sometimes run as a separate uninsulated single.
• Rubber wiring uses thinner conductors than PVC, since the rubber is higher temperature rated
• Rubber insulation perishes, cracks & falls off
• Properties with VIR cable are usually in urgent need of rewiring, and may represent a significant safety risk.

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 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.

Aluminium

• Cheaper alternative to copper
• Used from 1950s to 1970s, and old stock sometimes used into the 1980s.
• 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.

Copper Clad Aluminium

• An attempt to improve the properties of ali cable
• Significantly better than al, surface oxidation is eliminated, creep reduced & the risk from cracking more or less eliminated

Imperial T&E

Older T&E wiring having similar construction to today's cables.

• 7/.029 T&E
  • imperial 7 stranded version of 2.5mm² T&E
• Ashathene T&E
  • Precursor to PVC T&E
• PVC outer VIR inner
  • an early T&E cable
• 2 core T&E
  • 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 are usually in good condition, but rubber does not last well long term.

See Also

• Cables
• Wiki Contents
• Wiki Subject Categories
• Cable Sizes
• Wiring colour codes
• Cable Resistances