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D-89
Protective circuits
Additional informations
Designing the PEN conductor
The size of the PEN is determined in the same manner as a neutral conductor, i.e.:
for copper single-phase circuits or circuits with conductors sized
y
16 mm², the
PEN conductor must be the same size as the phase conductors
for copper three-phase circuits with conductors sized > 16 mm², it can be:
the same size as the phase conductors
smaller on the condition that:
the current likely to flow in the neutral during normal operation is less than the
permissible current for the conductor
the power rating of single-phase loads does not exceed 10 % of the total rating.
The PEN conductor must be accessible to enable connections both in the factory
and on site, as well as checks on the tightness of connections.
b
b
v
v
-
-
Implementing the PEN protective conductor
According to standard IEC 60439-1, the practical guidelines for implementing the
PEN are the following:
at the head of the assembly, the PEN connection must be near the phase
connections
within the assembly, the PEN does not need to be insulated from the exposed
conductive parts (except on sites where there is a risk of fire or explosion)
the size of the conductor must be at least equal to that of the neutral
the size must remain constant throughout the main busbars
the change from the TNC to the TNS system must take place at a single place in
the switchboard, via a marked neutral-disconnection bar that is accessible and can
be dismantled to facilitate the impedance measurement of the fault loop
after the TNS creation point, it is forbidden to recreate a TNC system.
The PE and the neutral must meet their individual constraints.
b
b
b
b
b
b
DD381655
PEN kit for Linergy busbars
see page B-73.
Practical information