Connection Points For Earthing And Short-Circuit Devices - Siemens Sivacon S8 Planning Information

2.4 Connection points for earthing
and short-circuit devices
Short-circuiting and earthing devices (SED)
For short-circuiting and earthing, short-circuiting and
earthing devices (SED) are available. For mounting the SED,
appropriate fastening points are fitted at the points to be
earthed. To accommodate the SED for the main busbar, a
cubicle for customized solutions is inserted (see Chapter
6.3 "Cubicle for customized solutions"). The cubicle widths
are given in Tab. 2/8.
Central earthing point (CEP) and main earthing busbar
(MEB)
When voltage sources, which are located far apart, are
earthed, for example secondary unit substation and
standby generator set, the separate earthing of their neu-
tral points results in compensating currents through foreign
conductive building structures. Undesired electro-magnetic
interference is created, caused by the building currents on
the one hand and the lack of summation current in the
respective cables on the other.
If the requirement is parallel operation of several voltage
sources and if building currents shall be reduced as far as
possible, the preferable technical solution is implementing
the central earthing point (CEP). In this case, the neutral
points of all voltage sources are connected to the system
protective conductor / system earth at a single point only.
The effect is that despite potential differences of the
neutral points, building currents cannot be formed any
more.
Tab. 2/8: Cubicle widths for earthing short-circuit points
Earthing and short-
Cubicle widths
circuit points
Short-circuiting and 400 mm (200 mm as cubicle
earthing devices (SED) extension)
Central earthing point 600 mm, 1,000 mm (200 mm as
(CEP) cubicle extension)
Main earthing busbar
600 mm, 1,000 mm
(MEB)
The central earthing point can only be used in the
power supply system L1, L2, L3, PEN (insulated) + PE.
To implement the central earthing point (CEP) - with or
without a main earthing busbar (MEB) - a cubicle for
customized solutions is inserted (see Chapter 6.3 "Cubicle
for customized solutions").
CEP design
The CEP is designed as a bridge between the separately
wired (insulated) PEN and the PE conductor of the switch-
board. Measuring current transformers can be mounted on
the bridge for residual current measurements. In order to
be able to remove the current transformer in case of a
defect, a second, parallel bridge is provided. This prevents
cancelling the protective measure due to a missing connec-
tion between the separately wired PEN and PE conductor.
A mounting plate in the cubicle is provided for placing the
residual-current monitors. The cubicle widths are given in
Tab. 2/8.
MEB design
In addition to the central earthing point, the MEB can
optionally be mounted as a horizontal bar. This connecting
bar is separately installed in the cubicle and rigidly con-
nected to the PE conductor. Depending on how the cable is
entered, the MEB is installed at the top or bottom of the
cubicle. The cubicle widths can be found in Tab. 2/8 and
information about the cable terminals can be found in
Tab. 2/9.
Tab. 2/9: Cable terminal for the main earthing busbar
Max. number of cables connectible with
Cubicle width
cable lug DIN 46235 (screw)
600 mm 10 x 185 mm
1,000 mm 20 x 185 mm
1)
300 mm² cable lugs can be used with M12 screw,
but this cable lug does not comply with DIN 46235, although it is
supplied by some manufacturers.
SIVACON S8 Planning Principles – SIVACON S8 – System overview
2 2 1)
(M10) + 12 x 240 mm (M12)
2 2 1)
(M10) + 22 x 240 mm (M12)
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