Difference between revisions of "Cables"
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Revision as of 11:45, 18 May 2007
Modern Cables
T&E
- L&N are PVC insulated, earth conductor is bare
- All 3 are sheathed with PVC
- Most domestic cable is T&E
- 1mm² 1.5mm² & 2.5mm² have non-stranded conductors
- 4mm², 6mm², 10mm² & 16mm² are stranded
Singles
- PVC insulated single conductors
- Used for a minority of domestic work
- For earth & equipotential bonding
- Standard cable for use in conduit
LSF
- Low Smoke & Fume
- Available in pretty purple
Armoured
- For outdoor & garden use
MICC
- aka pyro
- Copper tube sheath with magnesium oxide insulation
- Fireproof
- Rigid
- Occasionally seen in domestic premises, mainly in blocks of flats
- Widely used for fire alarm systems in commerce
- Prone to absorbing moisture from the air
- Hence does not always combine well with RCDs
- Special cable terminations required
- Ideal for flammability risk areas, eg traversing a thatched roof.
Historic Cables
Paper
- Paper insulation
- From the WW1 era
- Very rare now
PBJ
- PolyButyl Jute
- Common mains incomer insulation,
- Lots of old PBJ is still in service
Lead sheathed
- Common in 1930s for socket circuits
- Used as exterior farm cable well after that
- Lead sheath does not make good earth connections
- Rubber interior insulation
VIR
- Rubber insulated wiring
- The most common historic wiring
- Twisted pair cotton/rubber was very common
- Rubber wiring uses thinner conductors than PVC, since the rubber is higher temperature rated
- Rubber insulation perishes, cracks & falls off
- Most VIR wiring is now in a very bad way
- If you have a VIR instalation in use you have a safety problem.
Aluminium
- Cheaper alternative to copper
- Used at one time until its risks were realised
- Aluminium cable creeps, oxidises & fractures.
- Fire risk
- 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
Copper clad aluminium
- An attempt to improve the properties of ali cable
- Significantly better than al, surface oxidation is eliminated, creep reduced & the cracking risk more or less eliminated
T&E
- 7/.029 T&E
- imperial 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