The combined neutral and protective conductors (PEN) may exist
throughout the utility low-voltage distribution system, as this allows
some savings in the length of cables to be employed (i.e., four-wire
distribution system), whereas, within the user’s installation, neutral
and protective conductors may be separate (i.e., five-wire distribution
system). Insomecountries (e.g.,Norway, U.S.A.), the use of aPENconductor
downstream of the user’s main distribution panel is forbidden