earthing

1. Exercise 1:
Electrical Supply Systems
Aim:
To understand different types of supply systems and
trace the electrical supply system at UTAS Shinas

2. Electrical Power System in Oman
Reference:“PowerSystemGeneration,TransmissionandDistribution”,Presentationby Dr. AmerAl Hinai, AssistantProfessor,SQU,Oman

3. ❖ Electrical supply at the consumers (domestic/ commercial/
industrial) is drawn from distribution substations.
Depending on the applications and kVA the supply voltage is
11kV or 415 V.
❖ The distribution substations are equipped with necessary
means for isolation and protection.
❖ Bulk consumers of electricity such as UTAS Shinas receive
electrical supply at 11kV from distribution substation.
❖ In the consumer premises, the consumer has another
substation to step down this voltage to 415V to meet
lighting and low voltage applications.
Electrical Supply Systems

4. As per the Electricity Regulations applicable in the region to
ensure safety, electrical installations must be equipped with
Electrical Supply Systems
Basic protection Fault protection
Using Fuses
Using Proper Shielding
Using MCB’s
Using ELCB’s /RCD’s
This protection is provided using principle of “Protective
equi-potential bonding coupled with automatic
disconnection of supply”. In this method all exposed metal
work is electrically connected together to an effective earth
connection.
Principle of Fault Protection

5. Trunking
Metalwork of
electrical appliances
Water and Gas pipes
Central heating and air
conditioning systems
Electrical Conduits
Metal Framework
of building
Metal switches
Where & how to provide fault protection?

6. In this method all exposed metal work is electrically connected
together to an effective earth connection. This expose metalwork
includes,
➢ Electrical conduits Trunking
➢ Metal switches Metalwork of electrical appliances
➢ Water service pipes Gas and other service pipes and ducting
➢ Central heating and air-conditioning systems
➢ Exposed metallic structural parts of the building
➢ Lightening protective systems
Where & how to provide fault protection?

7. Basic Earthing Methods:
What is earthing?
In electricity supply systems, an earthing system defines
the electrical potential of the conductors relative to the Earth's
conductive surface.
There are three commonly used arrangements of the earthing
connection as described in IEE Electricity Regulations which are
discussed here.
1. TN-S System (Cable Sheath Earth Supply)
2. TN-C-S System (Protective Multiple Earthing Supply)
3. TT System (No Earth Provided Supply)

8. Notations
Letters T, N, C and S have been designated in the IEE Regulations for
identification of system.
T - Terre (French for earth) and meaning a direct connection to earth.
N - Neutral
C - Combined
S - Separate
• When these letters are grouped, they form the classification of a type of
system.
• The first letter denotes how the supply source is earthed.
• The second denotes how the metalwork of an installation is earthed.
• The third and fourth indicate the functions
of neutral and protective conductors

9. TT System
A TT system has a direct connection to the supply source to
earth and a direct connection of the installation metalwork to
earth. An example is an overhead line supply with earth
electrodes, and the mass of earth as a return path as shown
below.

10. Source: Basic Electrical Installation Work,Trevor Linsley

11. A TN-S system has the supply source directly connected to
earth, the installation metalwork connected to the neutral of
the supply source via the lead sheath of the supply cable, and
the neutral and protective conductors throughout the whole
system performing separate functions.
TNS System

12. Source: Basic Electrical Installation Work,Trevor Linsley

13. TN C S System
A TN-C-S system is as the TN-S but the supply cable sheath is also
the neutral, i.e. it forms a combined earth/neutral conductor
known as a PEN (protective earthed neutral)conductor. The
installation earth and neutral are separate conductors. This
system is also known as PME (protective multiple earthing).

14. Source: Basic Electrical Installation Work,Trevor Linsley

15. • Older houses in towns use TNS (solid) i.e. separate earth say
cable sheath
• Around Towns new houses use (PME) TNCS i.e. neutral and
earth shared
• Single House in country with own transformer uses TT i.e.
own buried earth electrode.
• Petrol stations, Swimming pools, Changing rooms etc. are
not allowed to be PME