GE AF-650 GP Design Manual page 156

7.9.3 Earthing of Screened/Armoured Control Cables
Generally speaking, control cables must be braided screened/armoured and the screen must be connected by means of a cable clamp at both ends to the metal
cabinet of the unit.
The drawing below indicates how correct earthing is carried out and what to do if in doubt.
a. Correct earthing
Control cables and cables for serial communication must be fitted
with cable clamps at both ends to ensure the best possible electrical
contact.
b. Wrong earthing
Do not use twisted cable ends (pigtails). They increase the screen
impedance at high frequencies.
c. Protection with respect to earth potential between PLC and fre-
quency converter
If the earth potential between the frequency converter and the
PLC (etc.) is different, electric noise may occur that will disturb the
entire system. Solve this problem by fitting an equalising cable, next
to the control cable. Minimum cable cross-section: 16 mm
d. For 50/60 Hz earth loops
If very long control cables are used, 50/60 Hz earth loops may occur.
Solve this problem by connecting one end of the screen to earth via
a 100nF capacitor (keeping leads short).
e. Cables for serial communication
Eliminate low-frequency noise currents between two frequency
converters by connecting one end of the screen to terminal 61. This
terminal is connected to earth via an internal RC link. Use twisted-
pair cables to reduce the differential mode interference between
the conductors.
7.9.4 Drives with Factory installed A1/B1 RFI Filter Option:
Mains supply isolated from earth
If the frequency converter is supplied from an isolated mains source ( IT mains, floating delta and grounded delta) or TT/TN-S mains with grounded leg, the RFI
switch is recommended to be turned off (OFF)
motors are connected or the motor cable length is above 25 m, it is recommended to set par. SP-50 RFI Filter to [ON].
1) Not available for 525-600 V frequency converters in frame sizes D, E and F.
In OFF, the internal RFI capacities (filter capacitors) between the chassis and the intermediate circuit are cut off to avoid damage to the intermediate circuit and
to reduce the earth capacity currents (according to IEC 61800-3).
It is important to use isolation monitors that are capable for use together with power electronics (IEC 61557-8).
2 .
1)
via par. SP-50 RFI Filter. For further reference, see IEC 364-3. In case optimum EMC performance is needed, parallel
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