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What are the different types of earthing systems ?

TT and TN-S schemes
b Single-phase circuits or those of c.s.a. y 16 mm2 (copper) 25 mm2 (aluminium): the
c.s.a. of the neutral conductor must be equal to that of the phases
b Three-phase circuits of c.s.a. > 16 mm2 copper or 25 mm2 aluminium: the c.s.a. of
the neutral may be chosen to be:
·         Equal to that of the phase conductors, or
·         Smaller, on condition that:
- The current likely to fl ow through the neutral in normal conditions is less than the
permitted value Iz. The infl uence of triplen(1) harmonics must be given particular
consideration or
- The neutral conductor is protected against short-circuit
- The size of the neutral conductor is at least equal to 16 mm2 in copper or 25 mm2 in
TN-C scheme
The same conditions apply in theory as those mentioned above, but in practice,
the neutral conductor must not be open-circuited under any circumstances since
it constitutes a PE as well as a neutral conductor
IT scheme
In general, it is not recommended to distribute the neutral conductor, i.e. a 3-phase
3-wire scheme is preferred. When a 3-phase 4-wire installation is necessary,
however, the conditions described above for TT and TN-S schemes are applicable.
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