Low voltage electrical distribution system earthing methods

TYPE OF EARTHING METHODS -
LOW VOLTAGE ELECTRICAL
DISTRIBUTION SYSTEM
By Raveendra Nath Macherla,
Senior Electrical Engineer
https://www.linkedin.com/in/raveendranath-macherla-9b303858/

TYPES OF DISTRIBUTION SYSTEM EARTHING
• TNS
• TNCS
• TNC
• TT
• IT
The following types of system
earthing are used in general:

UNDERSTANDING EARTHING SYSTEM CODES
• FIRST LETTER – RELATIONSHIP OF THE POWER SYSTEM (SOURCE) TO EARTH;
T = Direct connection of one point (example: star connected system neutral) to earth
I = All live parts isolated from earth (example: delta system), or one point (example: star connected system neutral) connected
to earth through an impedance
• SECOND LETTER – RELATIONSHIP OF THE EXPOSED-CONDUCTIVE-PARTS (EXAMPLE: ENCLOSURE/BODY OF LOAD) OF THE
INSTALLATION TO EARTH;
T = Direct electrical connection of exposed-conductive-parts to earth, independently of the earthing of any point of the power
system
N = Direct electrical connection of the exposed-conductive-parts to the earthed point of the power system (in a.c. Systems, the
earthed point of the power system is normally the neutral point or, if a neutral point is not available, a phase conductor).
• SUBSEQUENT LETTER(S) (IF ANY) – ARRANGEMENT OF NEUTRAL AND PROTECTIVE CONDUCTORS;
S = Protective function provided by a conductor separate from the neutral or from the earthed line (or in a.c. Systems, earthed
phase) conductor.
C = Neutral and protective functions combined as a single conductor (PEN conductor)

TN-S SYSTEM
(FIG:1)
single source
a.c. system

TN-S SYSTEM
(FIG:2)
single source
a.c. system

TN-S SYSTEM
(FIG:3)
single source
a.c. system

TN-C-S SYSTEM
(FIG:1)
single source
a.c. system

TN-C-S SYSTEM
(FIG:2)
single source
a.c. system

TN-C-S SYSTEM
(FIG:3)
single source
a.c. system

TN-C
SYSTEM:
single source
a.c. system

MULTIPLE a.c.
SOURCE SYSTEM
(FIG:1)
• In case of an inappropriate
design of an installation forming
part of a ‘TN’ system with
multiple sources some of the
operating currents may flow
through unintended paths.
These currents may cause
• - fire;
• corrosion;
• Electromagnetic interference.

MULTIPLE
a.c. SOURCE
SYSTEM
(FIG:2)

TT SYSTEM
(FIG:1):
single source
a.c. system

TT SYSTEM
(FIG:2):
single source
a.c. system

IT SYSTEM
(FIG:1)
single source
a.c. system

IT SYSTEM
(FIG:2)
single source
a.c. system

DC SYSTEM EARTHING
The decision whether to earth the positive or the negative pole of a two
wire d.c. system, shall be based upon operational circumstances or other
considerations, for example, avoidance of corrossion effects on line
conductors and earthing arrangements.

TN-S SYSTEM
(Type-a)
for d.c.
system

TN-S SYSTEM
(Type-b)
for d.c.
system

TN-C SYSTEM
(Type-a)
for d.c. system

TN-C SYSTEM
(Type-b)
for d.c. system

TN-C-S
SYSTEM
(Type-a)
for d.c.
system

TN-C-S
SYSTEM
(Type-b)
for d.c.
system

TT SYSTEM
(Type-a)
for d.c. system

TT SYSTEM
(Type-b)
for d.c. system

IT SYSTEM
(Type-a)
for d.c.
system

IT SYSTEM
(Type-b)
for d.c.
system

Thank you
Ref: IEC 60364 – Low Voltage Electrical Installations

Low voltage electrical distribution system earthing methods

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