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I assume they are using 7.12.3.1.3 to make that statement, that it is not allowed in the DB ? It is not so much as not allowed , just that it should be at the unit
On bigger systems where the transformer is owned by the client , it would need to be done in the transformer room or close to it , and could be the main D/Board for the installation if that is where the main neutral earth bar is
7.12.3.1.2 In an installation that is supplied from a combination of
transformers and alternative supplies located near to each other, the neutral
points of each of these items shall be connected to a single earthed neutral
bar (see P.1 and figure P.1). This earthed neutral bar shall be the only point
at which the neutral of the installation is earthed. Any earth leakage device
shall be positioned in such a way as to avoid incorrect operation due to the
existence of any parallel neutral/earth path.
7.12.3.1.3 Where alternative supplies are installed remotely from the
installation, or from one another, and where it is not possible to make use of
a single neutral bar or neutral conductor which is earthed, the neutral of each
unit shall be earthed at the unit and these points shall be bonded to the
consumer's earth terminal (see 6.12.4). The supply from each unit which
supplies the installation or part of the installation, shall be switched by means
of a switch that breaks all live conductors operating substantially together
(see figures P.2 and P.4), to disconnect the earthed neutral point from the
installation neutral when the alternative supply is not connected (see also
6.1.6).
7.16.4.3 Wherever the neutral is connected to the earth, a warning notice
shall be fitted to the outside of each distribution kiosk in the distribution
system, indicating "Neutral earthed inside".
On bigger systems where the transformer is owned by the client , it would need to be done in the transformer room or close to it , and could be the main D/Board for the installation if that is where the main neutral earth bar is
7.12.3.1.2 In an installation that is supplied from a combination of
transformers and alternative supplies located near to each other, the neutral
points of each of these items shall be connected to a single earthed neutral
bar (see P.1 and figure P.1). This earthed neutral bar shall be the only point
at which the neutral of the installation is earthed. Any earth leakage device
shall be positioned in such a way as to avoid incorrect operation due to the
existence of any parallel neutral/earth path.
7.12.3.1.3 Where alternative supplies are installed remotely from the
installation, or from one another, and where it is not possible to make use of
a single neutral bar or neutral conductor which is earthed, the neutral of each
unit shall be earthed at the unit and these points shall be bonded to the
consumer's earth terminal (see 6.12.4). The supply from each unit which
supplies the installation or part of the installation, shall be switched by means
of a switch that breaks all live conductors operating substantially together
(see figures P.2 and P.4), to disconnect the earthed neutral point from the
installation neutral when the alternative supply is not connected (see also
6.1.6).
7.16.4.3 Wherever the neutral is connected to the earth, a warning notice
shall be fitted to the outside of each distribution kiosk in the distribution
system, indicating "Neutral earthed inside".
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