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7. Special measures must be taken for the loads or parts of the
installation causing high leakage currents during normal operation
in order to avoid spurious tripping (feed the loads by insulating
transformers or use high threshold RCDs, compatible with the
exposed conductive part earth resistance).
8. Very high fault currents leading to maximum damage and
disturbance in telecommunication networks.
9. The risk for personnel is high while the fault lasts; the touch
voltages which develop being high.
10. Requires the use of differential protection devices so that the
fault clearance time is not long. These systems are costly.

(2) TN System: Neutral-connected exposed conductive part
• First letter T = the neutral is directly earthed at Transformer.
• Second letter N = the Frames of Electrical loads are connected to
the neutral Conductor.
There are two types of TN systems, depending on whether the
neutral conductor and Earth conductor are combined or not:
(2a) TN-C
• In TNC System (the third letter C = combined neutral and earth
conductor), the neutral and earth conductors are combined in a
single conductor and earthed at source end.
• This combined neutral-earth wire is than distributed to load side.
• In this system earthing connections must be evenly placed along
the length of the neutral-(earth) conductor to avoid potential rises
in the exposed conductive parts at Load Side if a fault occurs.
• This system must not be used for copper cross-sections of less
than 10 mm² and aluminum cross-sections of less than 16 mm², as
well as downstream of a TNS system (As per IEC 60364-5).

System Characteristics
1. Low earth fault loop impedance.
2. High earth fault current.
3. More than one earth fault loops.
Advantages
1. No earth wire required; allow multi-point earth.
2. Better earthing continuity.
3. Neutral never have float voltage.
4. Impedance of earth fault loop could be predicted.
5. The TNC system may be less costly upon installation

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