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10. Short-circuit and earth fault currents may cause fires and
destroy parts of the plant.

Earthed System
(1) TT system directly earthed neutral
• First letter T = the neutral is directly earthed.
• Second letter T = the exposed conductive parts of the loads are
interconnected and earthed.
• The transformer neutral is earthed.
• The frames of the electrical loads are also connected to an earth
connection.

System characteristics
1. High earth fault loop impedance.
2. Low earth fault current.
3. Utility company need not to provide earth for consumer.
Advantages
1. Save earth wires.
2. The big advantage of the TT earthing system is the fact that it is
clear of high and low frequency noises that come through the
neutral wire from various electrical equipment connected to it.
3. TT has always been preferable for special applications like
telecommunication sites that benefit from the interference-free
earthing.
4. Does not have the risk of a broken neutral.
5. The simplest system to design, implement, monitor and use.
6. Easily find location of faults.
7. Upon occurrence of an insulation fault, the short-circuit current
is small.
8. Reduces the risk of over voltages occurring.
9. Authorizes the use of equipment with a normal phase to earth
insulating level.
Disadvantages
1. High demand of Earth-Fault (E/F) relays.
2. Individual earth system needs higher investment.
3. Higher touch voltage.
4. Induce potential gradient.
5. Switching upon occurrence of the first insulation fault.
6. Use of an RCD on each outgoing feeder to obtain total
selectivity.

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