Great care should taken before undertaking extensions, alter-
ations repair that all conductors are correctly identified. Around
this sheath placed armour protection steel wires twisted along the
length the cable, and final PVC sheath covering the steel wires protects
them from corrosion. Both new and old cables must
be marked.1 shows sketch
of twin and earth cable.1. Figure 6.1
A twin and earth PVC insulated and sheathed cable.2).
Safety First
PVC cables
● PVC cables should not be
installed when the surrounding
temperature below 0°C. They are used where some mechanical protection
of the cable conductors required.
Cable core colours from 31st March 2004 onwards.
Sheath
Cable insulation
Stranded
copper conductor
FIGURE 6. Appendix 7671:
2008 deals with harmonized cable core colours.
● The PVC insulation becomes brittle
at low temperatures and may be
damaged during installation.
Alterations three-phase installations must marked the interface L1,
L2, for the lines and for the neutral.
PVC/SWA cable
PVC insulated steel wire armour cables are used for wiring underground
between buildings, for main supplies dwellings, rising sub-mains and
industrial installations. These markings are preferred coloured tape and caution
notice again required the distribution board.
The conductors are covered with colour-coded PVC insulation and then
contained singly with others PVC outer sheath.2.
● IEE Regulation 522. 6.
The conductors are covered with colour-coded PVC insulation and then
contained either singly with others PVC sheath (see Fig.
Extensions alterations existing single-phase installations not
require marking the interface between the old and new fixed wiring
colours.
PVC insulated and sheathed cables
Domestic and commercial installations use this cable, which may be
clipped direct surface, sunk plaster installed conduit trunk-
ing. the simplest and least expensive cable. The armour sheath also provides the circuit protective
.Basic electrical circuits and cables
125
● Three-phase supplies brown, black and grey line conductors, blue neu-
tral conductors and green combined with yellow for earth conductors. However, warning notice must fixed the consumer unit or
distribution fuse board which states:
Caution this installation has wiring colours two versions BS
7671
