Specifications
5.7.3 Earthing of Screened/Armoured
Control Cables
Control cables should be braided, screened/armoured, and
the screen must be connected with a cable clamp at both
ends to the metal cabinet of the unit. Illustration 5.106
shows correct earthing examples.
PE
FC
PE
130BA051.11
PE PE
FC
PE PE
FC
100nF
PE
FC
69
FC
PE PE
PE
68
61
68
69
FC
PE
a
b
c
d
e
PLC etc.
PLC etc.
PLC etc.
PLC etc.
Equalizing cable
Min. 16mm
2
Illustration 5.106 Earthing Examples
a Correct earthing
b Incorrect earthing
c Protection from potential between PLC and frequency
converter
d 50/60 Hz earth loops
e Cables for Serial Communication
Table 5.84 Legend to Illustration 5.106
a.
Correct earthing
Control cables and cables for serial communi-
cation are fitted with cable clamps at both ends
to ensure the best possible electrical contact.
b.
Incorrect earthing
Do not use twisted cable ends (pigtails). They
increase the screen impedance at high
frequencies.
c.
Protection from potential between PLC and
frequency converter
If the earth potential between the frequency
converter and the PLC (etc.) is different, electric
noise that disturbs the entire system is possible.
Fit an equalising cable, next to the control cable.
Minimum cable cross-section: 16 mm
2
.
d.
For 50/60 Hz earth loops
Using long control cables sometimes causes
50/60 Hz earth loops. Connect one end of the
screen to earth via a 100 nF 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.
5.8 Residual Current Device
Use RCD relays, multiple protective earthing or earthing as
extra protection in compliance with local safety
regulations.
If an earth fault appears, a DC content may develop in the
faulty current.
If using RCD relays, observe local regulations. Relays must
be suitable for protecting 3-phase equipment with a
bridge rectifier and for a brief discharge on power-up. See
2.11 Earth Leakage Current for more information.
How to Install VLT® HVAC Drive FC 102 Design Guide
154 MG16C102 - Rev. 2013-08-20
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