Grounding Of Shielded/Armored Control Cables - Danfoss VLT AutomationDrive FC 300 Design Manual

FC 300 Design Guide

Grounding of Shielded/Armored Control Cables

"
Generally speaking, control cables must be braided shielded/armored and the shield 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 grounding is carried out and what to do if in doubt.
Correct grounding
a.
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 grounding
Do not use twisted cable ends (pigtails).
They increase the shield impedance at
high frequencies.
Protection with respect to ground potential
c.
between PLC and VLT
If the ground potential between the adjustable
frequency drive and the PLC (etc.) is different,
electric noise may occur that will disturb
the entire system. Solve this problem
by fitting an equalizing cable, next to the
control cable. Minimum cable cross-section:
0.025 in. 2 (16 mm
For 50/60 Hz ground loops
d.
If very long control cables are used, 50/60 Hz
ground loops may occur. Solve this problem by
connecting one end of the shield to ground via
a 100nF capacitor (keeping leads short).
Cables for serial communication
e.
Eliminate low-frequency noise currents
between two adjustable frequency drives by
connecting one 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.
How to Install
2 ).
MG.33.B3.22 - VLT is a registered Danfoss trademark
109