II K 5-12
Installation
17
Others
18 Earthed public
low voltage
lines
The rated voltages of a public European low voltage line are 400 V
between the 3 phases and 230 V between a phase and the neutral
conductor. These voltages are provided by a transformer with its 3-
phase secondary winding in star connection. The star point is con-
nected with the neutral conductor and it is earthed at the trans-
former station. The electrical power is distributed by 4-wire cables
to the electricity consumers. At a cable stub to a consumer, the
neutral conductor must be earthed (local earth of the house or
plant
, and then it is split into a neutral and a PE conductor.
Therefore a 3-phase load with neutral conductor must be supplied
by a 5-wire cable. Converters, however, are 3-phase loads which
do not need the neutral conductor in most cases. They can be
supplied by 4-wire cables as shown in figure 5.2-1. The change
from the earthed neutral conductor outside the house, plant or
factory to the internal PE conductor with the local earthing point
between is not shown in this figure. See also section
24.
Power limitation: see end of section
4!
19 Public low volt-
age lines in in-
dustrial regions
In an industrial region the noise level which is caused by converters
is allowed to be 10 dB higher than in a residential region with in-
cluded light industry. Therefore the protection targets concerning
EMC can be met without screened motor cables if these cables are
configured according to
14.
A public low voltage line of an industrial region may have an own
supply transformer as shown in figure 5.2-1, but often the lines of
an industrial region and of a residential one are supplied by a
common transformer. This depends on the power consumption of
both regions and on their distance. Power limitation: see end of
4!
The dashed line between the lines of both regions indicates the
version with only one transformer, the one at extreme right in figure
5.2-1. This dashed line represents a power cable from the trans-
former at the right to the industrial region at the left.
The power cable is important also for the EMC. Due to its length it
reduces the noise level by at least 10 dB from the industrial to the
residential region.
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