Grounding Of Shielded/Armored Control Cables; Residual Current Device - Danfoss VLT Micro Drive FC 51 Design Manual

How to Install
6.10 Grounding of Shielded/Armored
Control Cables
Braid and shield/armor the control cables. Connect the
shield to the metal cabinet of the unit with a cable clamp
at both ends. Illustration 6.11 shows correct grounding
examples.
PLC etc.
PE
PLC etc.
PE
PLC etc.
PE
PE
Min. 16mm
Equalizing cable
PLC etc.
PE
100nF
FC
69
68
61
a Correct grounding
b Incorrect grounding
c Protection from potential between PLC and frequency
converter
d 50/60 Hz ground loops
e Cables for serial communication
Illustration 6.11 Grounding Examples
MG02K402
Design Guide
FC
PE
a
FC
PE
b
FC
PE
PE
c
2
FC
PE
d
FC
68
69
PE
e
Danfoss A/S © 01/2016 All rights reserved.
a. Correct grounding
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 grounding
Do not use twisted cable ends (pigtails). They
increase the shield impedance at high
frequencies.
c. Protection from potential between PLC and
frequency converter
If the ground potential between the frequency
converter and the PLC is different, electric noise
that disturbs the entire system is possible. Fit an
equalizing cable, next to the control cable.
Minimum cable cross-section: 16 mm
For 50/60 Hz ground loops
d.
Long control cables sometimes causes 50/60 Hz
ground loops. Connect 1 end of the shield to
ground via a 100 nF capacitor (keeping leads
short).
Cables for serial communication
e.
Eliminate low-frequency noise currents between 2
frequency converters by connecting 1 end of the
shield to terminal 61. This terminal is connected
to ground via an internal RC link. Use twisted-pair
cables to reduce the differential mode
interference between the conductors.

6.11 Residual Current Device

If local safety regulations are complied with, use RCD
relays, multiple protective grounding, or grounding as
extra protection.
If an ground fault appears, a DC content may develop in
the faulty current.
If RCD relays are used, observe local regulations. Relays
must be suitable for protection of 3-phase equipment with
a bridge rectifier and for a brief discharge on power-up,
see chapter 3.4 Ground Leakage Current for further
information.
6 6
2 (4 AWG).
49