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Mechanical and Electrical Systems
SKAA 2032
Electrical Wiring
Dr. Asrul Izam Azmi
Faculty of Electrical Engineering
Universiti Teknologi Malaysia
Announcement
Assignment 1
Solution will be given this week
Assignment 2:
Questions will be given this week
Mid-Term Exam:
Next Week (Monday, 22 Oct), 9am-10am
Tutorial Topic
Outline
Electrical Distribution and Wiring
• Wiring system, Types and size of cables
• Protections and Grounding
• Substation, Switchboard and Distribution Board
• Electrical Load (Estimation)
• Symbols and Single line diagram
Focus on receiving end
Component Elements of Electrical Cables
Selecting a cable for an electrical installation is very
important; consideration must be given to the following
criteria in order to ensure the correct type of cable is
chosen:
• conductor material
• conductor size
• insulation
• environmental conditions.
Conductor material
Copper and Aluminium
• The choice generally is between copper and
aluminium. Copper has better
• Conductivity for a given cross-sectional area and is
preferable, but its cost has risen over the years.
• Aluminium conductors are now sometimes preferred
for the medium and larger range of cables.
• All cables smaller than 16mm2 cross-sectional area
must have copper conductors.
Conductor material
Conductor material
Other conductor materials
• Cadmium copper: has a greater tensile strength for
use with overhead lines.
• Steel reinforced aluminium: for very long spans on
overhead lines.
• Silver: used where extremely good conductivity is
required. However, it is extremely expensive.
• Copperclad (copper-sheathed aluminium): cables
that have some of the advantages of both copper
and aluminium but are difficult to terminate.
Conductor size
There are many factors that affect the choice of size of
conductor
Load and future development
The current the cable is expected to carry can be found
from the load, taking into account its possible future
development, i.e. change in use of premises, extensions or
additions.
Ambient temperature
The hotter the surrounding area, the less current the cable
is permitted to carry.
Conductor size
Grouping
If a cable is run with other cables then its current carrying
capacity must be reduced.
Type of protection
Special factors must be used when BS 3036 (semi-enclosed)
fuses are employed.
Voltage drop
The length of circuit, the current it carries and the crosssectional area of the conductor will affect the voltage drop.
Insulation and sheathing
Listed below are some of the working properties of the
more common types of cable insulation:
• PVC
• synthetic rubbers
• silicon rubber
• magnesium oxide
• phenol-formaldehyde
Insulation and sheathing
PVC
This is a good insulator: it is tough, flexible and cheap. It is easy
to work with and easy to install. However, thermoplastic
polymers such as PVC do not stand up to extremes of heat and
cold, ordinary PVC cables should not constantly be used in
temperatures above 60°C or below 0°C. Care should be taken
when burning off this type of insulation (to salvage the copper)
because the fumes produced are toxic.
Synthetic rubbers
These insulators, such as Vulcanised Butyl Rubber, will withstand
high temperatures much better than PVC and are therefore used
for the connection of such things as immersion heaters, storage
heaters and boiler-house equipment.
Insulation and sheathing
Silicon rubber
FP 200 cable using silicon rubber insulation and with an
extruded aluminium oversheath foil is becoming more
popular for wiring such things as fire-alarm systems.
This is due largely to the fact that silicon rubber retains
its insulation properties after being heated up or
burned and is somewhat cheaper than mineralinsulated metal-sheathed cables.
Insulation and sheathing
Many factors affect cable selection. Some will be
decided by environmental factors:
• risk of excessive ambient temperature
• effect of any surrounding moisture
• risk of electrolytic action
• proximity to corrosive substances
• risk of damage by animals
• effect of exposure to direct sunlight
• risk of mechanical stress
• risk of mechanical damage.
Color
coded
conductor
Switching Circuit
One-way switching
Two-way switching
3 – Pin Plug
• the blue wire is connected to the neutral terminal;
• the brown wire is connected via a fuse to the live terminal;
• the green & yellow wire (when fitted) is connected to the earth terminal (the
two colours are used for the benefit of people who are colour-blind);
• the cable should be secured in the plug by the cable grip;
• a fuse of the correct value (rating) should be in place.
• the pins are made from brass, which is a good conductor;
• the plastic or rubber case, cable grip and fuse are for safety.
Errors in Wiring Plugs
1. Bare wires showing
2. Proper fuse not installed
3. Earth wire not connected
4. Live and neutral swapped
5. Loose cable grip
Plug and Socket
Japanese unearthed
sockets with a grounding
post for a washing
machine.
A North American
grounded (earthed) plug.
British Standard (BS)
1363 plug
CEE 7/16 plug and socket
(Europe countries)
23-16/VII with socket
(Italy)
M Plug (south Africa)
A type M (15 A version of type
D) travel adapter
Terminology
Terms
Meaning
Main power
House electrical power supply
Earth connection
Safety connection to the earth or ground
Live connection
Active connection
Neutral connection
Return connection
Flex/mains lead
Main wire/wiring
Flexible electrical cable from plug to
appliance
Socket, electrical wall outlet, power point
Female part of an electrical connection or
electrical fitting in a wall outlet
Pin, plug
Male part of an electrical connection
Potential Hazards
Electrocution.
• The least you can expect from touching a live wire is a severe
belt. If you are sweaty or wet, you can get a severe burn or even
be killed. The current does not need to be very large to cause a
a severe burn or death, especially if you are sweaty or wet
Electrical fires.
• A short circuit or other electrical fault in an appliance can make
too big a current flow. This can melt and set fire to wires,
sockets etc. When too big a current flows through the wiring
they get hot, just like toaster elements, and ignite building
materials such as timber, insulation, etc. Electrical fires can be
very dangerous - especially in timber-framed buildings, because
they often start inside a wall. They can burn there for quite a
while without being noticed. The main job of the fuse or circuit
breaker is to stop too large a current from starting a fire.
Shock
Current
( mA)
Effect
> 25
DEATH
10 - 25
PAIN. Can’t let go
0-10
TINGLE
Resistance – 4 KΩ (moist skin) to 24 KΩ (dry skin)
Safe current (through chest) – less than 20 milliamps
V = 240 VAC
R = 4 KΩ I = 60mA
I = 30 milliamps - NOT SAFE
The Sources of Electrical Hazards
There are various electrical hazards within the
home/office : • Long or frayed cables
• Cables in contact with something hot or wet
• Water near sockets
• Shoving things into sockets
• Damaged plugs
• Connection of too many plugs within a socket
• Lighting sockets without bulbs in
• Appliances without covers
• Short circuit
Electrical Control Measures/Circuit Protection
1. Insulation
2. Earthing/Grounding
3. Fuses
4. Circuit breakers
1. Insulation
Insulation
Outer sleeve (jacket)
(a) Cables have a flexible
plastic outer sleeve and the
wires inside also have their
own flexible plastic sleeves.
These sleeves act as insulation
layers which stop the copper
core of the live wire from
contacting the other wires,
any metal part, or the skin of
anybody that is touches the
wire.
Insulation
(b) Plug casings
Plug casing are made of plastic or rubber.
Molded plugs attached at the factory are
molded to the cable and are even safer than
the plugs that you can take apart.
Insulation
(c) Double insulation
• An electrical appliance which is double insulated
does not have an earth wire fitted
• The appliance that not only has insulated wires
inside, but also has a casing made of plastic, so
that they provide two level of protection against
electrical shock.
• Common double insulated appliances are hair
dryers, radios and cassette players.
Symbol
2. Earthing/Grounding
Earthing/Grounding
• The earth wire is a safety feature which
prevents the metal casing of an appliance
becoming dangerous to touch when a fault
occurs.
• Many electrical appliances have metal cases,
including cookers, washing machines and
refrigerators – the earth wire creates a safe
route for the current to flow through if the live
wire touches the casing.
• You will get an electric shock if the live wire
inside an appliance, such as a cooker, comes
loose and touches the metal casing.
Earthing/Grounding
• The earth terminal is connected to the metal
casing so that the current goes through the
earth wire instead of causing an electric shock
• A strong current surges through the earth wire
because it has a very low resistance – this
breaks the fuse and disconnects the appliance
Earthing/Grounding
Earth Electrodes
• Variety of types of earth electrode including earth
rods, plates electrodes, wire electrodes ground
ring electrodes and underground structural metal
work
• There are certain requirements such as the soil
resistivity, depth of grounding and types and
dimension of electrodes
Rod
Wire electrodes
Plate electrodes
Earthing/Grounding System
• Major types of earthing system:
– TN-S
– TN-C
– TT
•
•
•
•
T: Earth
N: Neutral
S: Separate
C: Combined
TN-S Earthing System
• A TN-S system, has the neutral of the source of energy connected
with earth at one point only, at or as near as is reasonably practicable
to the source, and the consumer's earthing terminal is typically
connected to the metallic sheath or armour of the distributor's
service cable into the premises.
TN-C-S Earthing System
• The supply neutral conductor of a distribution main connected with earth at
source and at intervals along its run. This is usually referred to as protective
multiple earthing (PME). With this arrangement the distributor's neutral
conductor is also used to return earth fault currents arising in the
consumer's installation safely to the source. To achieve this, the distributor
will provide a consumer's earthing terminal which is linked to the incoming
neutral conductor.
TT Earthing System
• The neutral of the source of energy connected as for TN-S, but no
facility is provided by the distributor for the consumer's earthing.
With TT, the consumer must provide their own connection to earth,
i.e. by installing a suitable earth electrode local to the installation.
This type of earthing arrangement is commonly found in rural areas.
3. Fuses
Fuses
• An electric fuse is a device which is used to limit the
current in an electric circuit.
• The fuse protects the circuit and the electrical
appliances from being damaged – when there is too
much current, the fuse melt.
• Fuses in plugs are made in standard ratings (3A, 5A, 13A
etc…)
symbol
Fuses
• The fuse wire is generally an alloy of lead and
tin. It has a low melting point and breaks the
circuit if the current exceeds a safe value.
• The thickness and length of the fuse wire
depends on the maximum current allowed
through the circuit.
• It is connected in series in the beginning of the
electric circuits.
• Short circuit, overloading, mismatched loads or
device failure are the prime reasons for
excessive current.
Fuses
• When the circuit current exceeds a specified value
due to voltage fluctuations or short-circuiting, the
fuse wire gets heated and melts.
• Thus it breaks
the connection
as shown in the
figure and no
current flows.
This prevents
damage to the
appliance.
Fuses
Fuses
• To choose the correct fuse for an electrical
device, always choose the one with the closest
rating that is greater than the operating
current of the device.
• Example, if a kettle operates with an electrical
current of 10A, what fuse should it be fitted
with (from 3A, 5A and 13A)? Ans: 13A
• Other example, If a device operates at 3A,
choose 5A fuse.
• Different appliances require different sized fuses:
– A cooker - 30 Amp, A lighting circuit - 5A, A table lamp - 3A, An electric
kettle, 13A
4. Circuit breakers
Circuit Breaker
• A circuit breaker (CB) is an automatically operated
electrical switch designed to protect an electrical circuit
from damage caused by overload or short circuit.
• The basic function is to detect a fault condition and, by
interrupting continuity, to immediately discontinue
electrical flow.
• Unlike a fuse, which operates once and then must be
replaced, a circuit breaker can be reset (either manually
or automatically) to resume normal operation.
• Circuit breakers are made in varying sizes, from small
devices that protect an individual household appliance
up to large switchgear designed to protect high voltage
circuits feeding an entire city.
Circuit Breaker
1. Actuator lever
2. Actuator mechanism
3. Contacts
4.Terminals
5. Bimetallic strip
6. Calibration screw
7.Solenoid
8. Arc divider / extinguisher
Circuit Breaker
Switching mechanisms used in circuit breaker
• Low voltage circuit breakers
• Magnetic circuit breakers
• Thermal magnetic circuit breakers
• Common trip breakers
• Medium-voltage circuit breakers
Circuit Breaker
Types of circuit breaker
• MCB (Miniature Circuit Breaker)
• MCCB (Moulded Case Circuit Breaker)
• Air Circuit Breaker
• Vacuum Circuit Breaker
• RCD (Residual Current Device) / RCCB( Residual
Current Circuit Breaker)
• ELCB (Earth Leakage Circuit Breaker)
• RCBO (Residual Circuit Breaker with Overload)
Circuit Breaker
MCB (Miniature Circuit Breaker)
– Rated current not more than 100 A.
– Trip characteristics normally not adjustable.
– Thermal or thermal-magnetic operation.
• MCCB (Moulded Case Circuit Breaker):
– Rated current up to 1000 A.
– Trip current may be adjustable.
– Thermal or thermal-magnetic operation.
Circuit Breaker
Vacuum Circuit Breaker:
– With rated current up to 3000 A,
– These breakers interrupt the arc in a vacuum bottle.
– These can also be applied at up to 35,000 V. Vacuum
breakers tend to have longer life expectancies between
overhaul than do air circuit breakers.
ELCB (Earth Leakage Circuit Breaker)
– Phase (line), Neutral and Earth wire connected through
ELCB.
– ELCB is working based on Earth leakage current.
Circuit Breaker
RCD (Residual Current Device / RCCB(Residual
Current Circuit Breaker)
• Phase (line) and Neutral both wires connected
through RCD
• It trips the circuit when there is earth fault current.
• The amount of current flows through the phase
(line) should return through neutral .
• It detects by RCD. any mismatch between two
currents flowing through phase and neutral detect
by -RCD and trip the circuit within 30 miliseconed.
• RCDs are an extremely effective form of shock
protection
Magnetic Circuit Breaker
Circuit breakers
work quicker
than fuses.
( saves lives)
Magnetic Circuit Breaker
Question
a) What is the main purpose of a wire fuse or
circuit breaker?
b) Explain how a wire fuse protects an appliance
if it develops a fault.
c) Explain how a wire fuse and an earth
connection stop you getting an electric shock if
an appliance develops a fault.
Question
d) In a modern home, each wiring circuit is
protected by a circuit breaker rather than a wire
fuse. Give two advantages of a circuit breaker
compared with a wire fuse.
– Circuit breaker can be reset when tripped, while
fuse need to be replaced.
– Safer to reset, flick a switch. No human error
because there is no replacing of fuse wire
manually.
– Longer life
Typical wiring system
Typical wiring system
Why are sockets wired
in parallel with
each other ?
Consumer Unit / Distribution Board
• A consumer unit is a type of distribution board (a component of
an electrical power system within which an electrical power
feed provides supply to subsidiary circuits).
• Consists of fuses, circuit breakers and residual current operated
devices.
Dual RCD split load board