Wiring Installation

WIRING INSTALLATION
Complied and Presented by

Doren Nedrick
Wiring Installation
The
service entrance includes all the parts of the

assembly that bring electricity into a building.
Its conductors extend from the point at which the
service-drop conductors are attached at the house
to the load center. The complete service entrance
is generally thought to include the conductors, the
watt-hour meter, and the load center.
Usually the power company takes care of the
wiring from the power line up to and including the
meter.
2
Service-entrance Cables
The
service-entrance cable has three

conductors. One of these, the neutral
conductor, is bare.
When the cable is to be connected to a
terminal point, the strands of the
conductor are twisted together to form a
single-stranded conductor.
Pictorial diagram of a Domestic

Installation
The Watt Hour Meter

Watt-hour
meters measure and record the

amount of electric energy (in kilowatt-hour
units) supplied to a building. The meter is
usually, but not always, installed by and
belongs to the power company.
Load Center
Load
centers, also called fuse or circuit-breaker

panels, are the boxes from which electricity can
be distributed to different locations in a house. It
contains the main breaker or fuses that can
disconnect all the electrical service from a
house.
The load center also contains the fuses or circuit
breakers that protect the branch circuits of the
wiring system. The size of the load center is
designated by the number of fuses or circuit
breakers that can be placed into it, and by its
load, or ampere, rating.
6
Service Grounds
To reduce
the danger of shock and to

protect against lightning, the bare
conductor of the service entrance cable is
grounded at the meter socket by being
connected an earth rod. This is the safety
ground.
This neutral wire is further connected to
the neutral bus bar and earth lug in the
load center.
7
BRANCH CIRCUITS
Branch
circuits of a residential wiring

system distribute electricity from the load
center to the rooms of the house. The
three common kinds of branch circuits are
discussed below.
General-Purpose Circuits
General-purpose
branch circuits are

used for lighting and outlets. The outlets
are intended to serve radios, television
sets, clocks, and other small appliances
used for food preparation (such as
toasters, broilers, etc.). Lighting circuits
are usually wired with number 1.5mm 2
cable and are protected with 15A fuses or
circuit breakers, respectively
9
Connecting Convenience Outlets

one
wire of each general-purpose circuit is

connected to the neutral bus bar of the load
center. The grounded neutral wire is color coded
black. The wire connected directly to the fuse or
circuit breaker is generally red. This circuit wire
is often called the hot wire. The grounded black
wire of a two-wire, general-purpose circuit is
never used as a safety grounding wire. When
the cabinet or case of a product operated from
such a circuit is to be grounded, a third
grounding wire is used.
10
Small Appliance Circuits

Small
appliance circuits are used for such

appliances as refrigerators, toasters,
broilers, coffee makers, and irons. They
are wired with number 2.5mm2 wires and
are protected with 20A fuses or circuit
breakers.
In practice a maximum of two (2) outlets
should be placed in the kitchen circuits
11
Individual Circuits
An
individual circuit is used for only one piece of

equipment. Examples of individual circuits are
those used with electric ranges, dryers, water
heaters, heating systems, and air conditioners.
A range circuit is usually a four-wire, 220 V
circuit. It has two hot wires, a neutral wire, and a
ground. There is a fuse or circuit breaker in each
of the hot wires and are ganged.
Called double pole circuit breaker
12
Circuit breaker Rating for individual circuit

There
current rating is based on its

wattage.
Example: An 8kW, 220V range will draw
I = P/V
= 8000/220
= 36.36A
Therefore a 40A Double pole CB should
be used to protect the circuit
13
Types of Wiring Methods

Non-metallic
Conduit: When wiring needs to

be protected from the environment, either
because of the weather safety considerations or
to protect it from mechanical damage, a conduit
system is used.
Non-metallic conduit systems have the following
advantages: absence of condensed moisture in
the tube, non-corrosive (rust-free), noninflammable.
14
Preparing the Conduit:

Conduit
comes in lengths (usually about 3.5 m)

and is threaded at both ends.
Cutting: Lengths should be cut to size with a
hack saw having a fine tooth blade. The blade
must be held at right angles to the conduit
during cutting. Conduit should always be cut in a
pipe vice.
The thread is cut by using stocks and dies
Bending Conduit: Conduit can be bent with
either a bending spring, bending block or a
bending machine.
15
Bending Rigid Conduit
16
Termination
of Conduit. Metallic conduit

must always be terminated at an
incombustible outlet, preferably a metal
box.
17
Non Metallic Sheathed Cable

Nonmetallic
sheathed cable usually has two or

three insulated wires and a grounding wire.
NM cable is used for all kinds of indoor wiring
work and is never to be buried in cement or
plaster hence its use in board house. NM cable
has a moisture-resistant overall covering, which
allows it to be used for both exposed and
concealed work in dry, moist, and damp
locations, and on outside or inside walls of
masonry, block, or tile.
18
PVC Trunking
19
Regulations Regarding Electrical

Installation
1.
All cables must be rated at, or above, the

current which they will normally be expected to
carry without undue heating or voltage drop
(normally 2.5 per cent of nominal voltage).
2. All conductors, cables and equipment used in
the installation must be of the correct Voltage
rating, for example, 250V grade switchgear
should not be used on 415V 3-phase
installations: 500V switchgear is necessary.
3. The fuse in a circuit must be capable of
protecting the smallest conductor in that circuit.
20
Regulations Continued
4. All conductors and equipment must be properly

labelled; this saves time and also minimizes the danger
of opening the wrong circuit when isolating or faultfinding.
5. All equipment must be protected against: high
temperatures, moisture, corrosion, and mechanical
damage.
6. The main distribution point should be situated, if
possible, at the centre of the installation in order to keep
cable runs short.
7. Sufficient capacity should be installed at the outset (in
main switches, bus-bar chambers, and cables) to allow
for future expansion.
21
Used for stairs and corridors

22
Used for long corridors in hospitals and schools
23
Testing
Verification
of Polarity Test The purpose

of the verification of polarity test is to
check that the phase conductor is taken
through the fuse or circuit breaker and the
switch to the appliance.
The neural must never be broken by a CB
or switch. If the CB opened under these
conditions, then the circuit would still be
live.
24
25
A case
was reported where a man was serious

electric shock while cleaning the reflector of an
electric fire with a damp cloth. The fire had been
switched off but the plug was not removed.
26
Preparation for verification of polarity test

Supply
off
Lamps and appliances out
All switches off, Neutral links in; fuses out
Test
Instrument
Ohm meter or bell set
Reading
Zero on ohmmeter and continuity on

the bell set. (The insulation resistance tester
megger should not be used as the smallest
reading is about 10 000)
27
Polarity test
28
29

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WIRING INSTALLATION

Complied and Presented by

service entrance includes all the parts of the

service-entrance cable has three

Pictorial diagram of a Domestic

The Watt Hour Meter

meters measure and record the

centers, also called fuse or circuit-breaker

the danger of shock and to

circuits of a residential wiring

branch circuits are

Connecting Convenience Outlets

wire of each general-purpose circuit is

Small Appliance Circuits

appliance circuits are used for such

individual circuit is used for only one piece of

Circuit breaker Rating for individual circuit

current rating is based on its

Types of Wiring Methods

Conduit: When wiring needs to

Preparing the Conduit:

comes in lengths (usually about 3.5 m)

Bending Rigid Conduit

of Conduit. Metallic conduit

Non Metallic Sheathed Cable

sheathed cable usually has two or

Regulations Regarding Electrical

All cables must be rated at, or above, the

4. All conductors and equipment must be properly

Used for stairs and corridors

Used for long corridors in hospitals and schools

of Polarity Test The purpose

was reported where a man was serious

Preparation for verification of polarity test

Zero on ohmmeter and continuity on

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