The document discusses the importance of earthing systems in electrical installations. An earthing system connects all metallic bodies of electrical equipment to the earth through a low resistance wire. This serves to protect humans from electric shock by providing an alternative path for fault currents. It also ensures exposed conductive parts do not reach dangerous potentials and maintains voltage stability. A good earthing system has low impedance to allow fault currents to quickly blow fuses and disconnect faulty circuits.

2. All the people living or working in residential,
commercial and industrial installations, particularly
the operators and personnel who are in close
operation and contact with electrical systems and
machineries, should essentially be protected against
possible electrification. To achieve this protection,
earthing system of an installation is defined,
designed and installed according to the standard
requirements..

3. The process of connecting metallic bodies of all the
electrical apparatus and equipment to huge mass of
earth by a wire having negligible resistance is called
Earthing.

4. • Provide an alternative path for the fault current to flow
so that it will not endanger the user
• Ensure that all exposed conductive parts do not reach a
dangerous potential
• Maintain the voltage at any part of an electrical system
at a known value so as to prevent over current or
excessive voltage on the appliances or equipment.

5. Good Earthing must have low impedance enough to
ensure that sufficient current can flow through the
safety device so that it disconnects the supply ( <0.4
sec ). Fault current is much more than the full load
current of the circuit which melts the fuse. Hence, the
appliance is disconnected automatically from the
supply mains.

6.  Must be of low electrical resistance
• Must be of good corrosion resistance
• Must be able to dissipate high fault current repeatedly

7. • To save human life from danger of electrical shock or death by
blowing a fuse i.e. To provide an alternative path for the fault
current to flow so that it will not endanger the user
• To protect buildings, machinery & appliances under fault
conditions ie. To ensure that all exposed conductive parts do
not reach a dangerous potential.
• To provide safe path to dissipate lightning and short circuit
currents.
• To provide stable platform for operation of
sensitive electronic equipments i.e. To maintain the voltage
at any part of an electrical system at a known value so as to
prevent over current or excessive voltage on the appliances or
equipment .
• To provide protection against static electricity from friction

8.  An electric shock (electrocution)occurs when two portion of a
person’s body come in contact with electrical conductors of a
circuit which is at different potentials, thus producing a
potential difference across the body.
 The human body does have resistance and when the body is
connected between two conductors at different potential a
circuit is formed through the body and current will flow
 When the human body comes in contact with only one
conductor, a circuit is not formed and nothing happens. When
the human body comes in contact with circuit conductors, no
matter what the voltage is there is potential for harm.

9.  When a high voltage such as 13,800V is involved the
body is literally cooked and at times explodes

10.  To analyze how an electrical shock occurs and how
grounding is applied you need to look at the circuit
involved.
 Fig 2 illustrates the basic circuit that consist of a
source, a transformer or generator for all AC circuits,
circuit protection, conductors(R1s), and a load (RL).

11.  In case of insulation failure, the primary object of
connecting all the above points and apparatus to earth
is to release the charge accumulated on them
immediately to earth so that the person coming in
contact may not experience electric shock.