This FAQ has been written for NEAL (North East Africa and Levant) region. If you are looking for information for another region, please select the correct country from the top-left dropdown in the page and 'Navigate to Browse FAQs' in the Support menu.
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
- The size of the neutral conductor is at least equal to 16 mm2 in copper or 25 mm2 in
aluminium
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.
Released for:Schneider Electric Egypt and North East Africa
