Residual Current Device - Danfoss VLT HVAC Drive FC 102 Design Manual

How to Install
5.7.3 Grounding of Shielded/Armored
Control Cables
Control cables should be braided, shielded/armored, and
the shield must be connected with a cable clamp at both
ends to the metal cabinet of the unit. Figure 5.106 shows
correct grounding examples.
Figure 5.106 Grounding Examples
a Correct grounding
b Incorrect grounding
c Protection from potential between PLC and adjustable
frequency drive
d 50/60 Hz ground loops
e Cables for Serial Communication
Table 5.84 Legend to Figure 5.106
MG16C122
Design Guide
a.
b.
c.
d.
e.

5.8 Residual Current Device

Use RCD relays, multiple protective grounding or
grounding as extra protection in compliance with local
safety regulations.
If a ground 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
chapter 2.11 Ground Leakage Current for more information.
Danfoss A/S © Rev. 2014-01-13 All rights reserved.
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.
Incorrect grounding
Do not use twisted cable ends (pigtails). They
increase the shield impedance at high
frequencies.
Protection from potential between PLC and
adjustable frequency drive
If the ground potential between the adjustable
frequency drive and the PLC (etc.) is different,
electric noise that disturbs the entire system is
possible. Fit an equalizing cable next to the
control cable. Minimum cable cross-section: 0.025
in 2 [16 mm 2 ].
For 50/60 Hz ground loops
Using long control cables sometimes causes
50/60 Hz ground loops. Connect one end of the
shield to ground via a 100 nF capacitor (keeping
leads short).
Cables for serial communication
Eliminate low-frequency noise currents between
two adjustable frequency drives by connecting
one end of the shield to terminal 61. This
terminal is grounded via an internal RC link. Use
twisted-pair cables to reduce the differential
mode interference between the conductors.
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