Using Shielded Control Cables; Grounding Of Shielded Control Cables - Danfoss VLT FC 103 Instruction Manual

Installation

2.5.2 Using Shielded Control Cables

Danfoss recommends braided shielded/armored cables to
optimize EMC immunity of the control cables and the EMC
emission from the motor cables.
The ability of a cable to reduce the incoming and
outgoing radiation of electric noise depends on the
transfer impedance (Z ). The shield of a cable is normally
T
designed to reduce the transfer of electric noise; however,
a shield with a lower transfer impedance (Z
effective than a shield with a higher transfer impedance
(Z ).
T
Transfer impedance (Z ) is rarely stated by cable manufac-
T
turers, but it is often possible to estimate transfer
impedance (Z ) by assessing the physical design of the
T
cable.
Transfer impedance (Z ) can be assessed on the basis of
T
the following factors:
•
The conductibility of the shield material
•
The contact resistance between the individual
shield conductors
•
The shield coverage, i.e., the physical area of the
cable covered by the shield - often stated as a
percentage value
•
Shield type, i.e., braided or twisted pattern
a. Aluminum-clad with copper wire
b. Twisted copper wire or armored steel wire cable
c. Single-layer braided copper wire with varying
percentage shield coverage.
This is the typical Danfoss reference cable.
d. Double-layer braided copper wire
e. Twin layer of braided copper wire with a
magnetic, shielded/armored intermediate layer
f. Cable that runs in copper tube or steel tube
g. Lead cable with 0.043 in [1.1 mm] wall thickness
®
VLT Refrigeration Drive Instruction Manual
) value is more
T
Figure 2.14

2.5.3 Grounding of Shielded Control Cables

Correct shielding
The preferred method in most cases is to secure control
and serial communication cables with shielding clamps
provided at both ends to ensure best possible high
frequency cable contact. If the ground potential between
the adjustable frequency drive and the PLC 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
[16 mm
Figure 2.15
1
2
Table 2.9
®
MG16J122 - VLT is a registered Danfoss trademark
2
].
PLC
PE PE
<10 mm
PE PE
1
2
2 2
Min. 0.025 in [16 mm ]
Equalizing cable
2
2
FC
2-13
2