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Resolver
To other
servo amplifiers
Mains
power
filter
+25 V
XGND
BRAKE
PE
U2
V2
W2
L1
L2
L3
+DC
–DC
X1
X6
X2
X5
PCRESOLVER
SW +
SW -
AGND
PSTOP
NSTOP
DGND
I/O
ENABLE
BTB
BTB
SHIELD
WPE
KLBÜ
KLBÜ
Shields
Earths
KLBÜ
KLBÜ
KLBÜ
Booster
Personal
computer
3
Control signals
digital analogue
Positioning signals
CNC – GND CNC – GND
CONTROLLER
Differences between earthing and shielding
The terms “earthing” and “shielding” are classied according
to their relation to human safety or facility safety. The earth
is installed primarily to protect human life and for this reason
is referred to as the protective earth conductor. On the
other hand, shielding is used to ensure that the electrical
system functions properly. It also ensures electromagnetic
compatibility.
These main differences between the two terms inuence the
electrical design and installation. Shielding is not designed
to transfer power, although leakage currents may ow on
them. A protective earth conductor, however, must be able
to briey discharge a high fault current (IEC 60947-7-2).
The short-term current resistance of the PE connection must
be 120 A/mm² for the connected cross-section.
The illustration below shows how these two topics relate to
each other in application.
As shown in the picture below, the cable’s shielding is
connected to the earth potential so that the
shield’s current can be discharged. Depending on the
sensitivity of the facility, isolated areas of potential can
be created. However it is still typical to mix the areas, so
that the shielding is on a common equipotential earth.
This illustration shows how the number of shields and PE
conductors that need to be connected can increase quite
rapidly (in this case only one component is used). The
shielding and earthing systems must be planned carefully to
provide adequate safeguards for personnel and equipment.
The following sections describe the complexity and
uniqueness in more detail.
Earthing for shielded cables
Connection diagram for a frequency converter
Different symbols are also used for
the two themes:
Shielding
Earthing
B
B.120 2028840000
Lightning and surge protection for control and instrumentation signals