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Introduction to Electrical installation

ELECTRICAL WIRING MATERIALS AND METHODS
Technical University of Mombasa
2
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Wiring systems in a single-family home or flat, for example, are simple, with
relatively low power requirements
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Heavy industries have more demanding wiring requirements, such as very large
currents and higher voltages
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Wires and cables
Wires and cables are the main part of electrical installation
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A wire or cable has a voltage (to neutral) rating and a maximum conductor surface
temperature rating
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Early wires and cables
 PI: Paper-insulated cable is introduced in the United Kingdom in 1896, consisting
of two impregnated paper-insulated conductors inan overall lead sheath
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Paper-insulated cables proved unsuitable for interior wiring installations because
very careful workmanship was required on the lead sheaths to ensure moisture
did not affect the insulation
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The metal sheath was bonded to each metal wiring device to ensure
earthing continuity
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Over time, rubber-insulated wires
and cables become brittle because of exposure to atmospheric oxygen, so they
must be handled with care, and are usually replaced during renovations
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 PVC: About 1950, PVC (polyvinyl chloride) insulation and jackets were
introduced, especially for residential wiring
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The simplest form of the cable has two insulated conductors twisted together to
form a unit; such unjacketed cables with two or three conductors are used for
low-voltage signal and control applications, see Fig
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Fig
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Copper conductors: Copper wire and cable
Electrical devices often contain copper conductors because of their multiple
beneficial properties, including:
high electrical conductivity,
high tensile strength,
high ductility,
corrosion resistance,
good thermal conductivity,
solderability,
resistance to electrical overloads,
compatibility with electrical insulators, and
ease of installation
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Aluminium conductors: Aluminium wires andcables
Aluminium wire was common in some countries residential wiring from the late
1960s to the mid-1970s due to the rising cost of copper
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Aluminium conductors were originally used with wiring devices intended for
copper conductors
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were specially designed for the
purpose
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Aluminium conductors must be
installed with compatible connectors
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Special versions of non-metallic sheathed cables, such as Type PVC
insulated PVC sheathed, are designed for direct underground burial (often
with separate mechanical protection) or exterior use where exposure to
ultraviolet radiation (UV) is a possibility
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Rubber-like synthetic polymer insulation is used in industrial cables and
power cables installed underground because of its superior moisture
resistance
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Building wire conductors
larger than 6 mm² (10 AWG) are stranded for flexibility during
installation, but are not sufficiently pliable to use asappliance cords
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Introduction to Electrical installation

Another form of high-temperature cable is a mineral insulated cable MICC,
with individual conductors placed within a copper tube, and the space filled
with magnesium oxide powder
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Such cables have a certified
fire-resistance rating and are more costly than non-fire-rated cables
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Raceways or electrical conduits
Electrical Conduit and Raceways are used to protect cables from damage
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This may be a specialized bendablepipe, called a conduit
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Metal conduit (rigid galvanized steel or Black Enameled Steel conduit), see
Fig
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2
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2
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Rectangular cross-section metal or PVC wire or Trunking (UK) may be used in
many circuits are required, see Fig
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Galvanized steel Conduit

Black Enameled Steel conduit
Fig
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2 Non-metallic (PVC or HDPE) pipes

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Introduction to Electrical installation

Fig
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Wires run underground may be run in plastic tubing encased in concrete, but metal
elbows may be used in severe pulls
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4

Conduit

5

accessories
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5 Conduit accessories
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6 PVC accessories
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Cable trays are used in industrial areas where many insulated cables are run
together
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Power cables
may have fittings in the tray to maintain clearance between the conductors, but
small control wiring is often installed without any intentional spacing between
cables
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Special sealed fittings are used for wiring routed through potentially explosive
atmospheres
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7 Cable trays

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