Use of EMC-correct cables
Braided screened/armoured cables are recommended
to optimise EMC immunity of the control cables and
the EMC emission from the motor cables.
The ability of a cable to reduce the in- and outgoing
radiation of electric noise depends on the switching
impedance (Z
T
). The screen of a cable is normally de-
signed to reduce the transfer of electric noise; howev-
er, a screen with a lower Z
T
value is more effective than
a screen with a higher Z
T
.
Z
T
is rarely stated by cable manufacturers, but it is of-
ten possible to estimate Z
T
by assessing the physical
design.
Z
T
can be assessed on the basis of the following fac-
tors:
-
The contact resistance between the individ-
ual screen conductors.
-
The screen coverage, i.e. the physical area
of the cable covered by the screen - often
stated as a percentage value. Should be min.
85%.
-
Screen type, i.e. braided or twisted pattern.
Aluminium-clad with copper wire.
Twisted copper wire or armoured steel wire cable.
Single-layer braided copper wire with varying per-
centage screen coverage.
Double-layer braided copper wire.
Twin layer of braided copper wire with a magnetic,
screened/armoured intermediate layer.
Cable that runs in copper tube or steel tube.
Lead cable with 1.1 mm wall thickness with full cov-
erage.
VLT
®
6000 HVAC Series
76 MG.61.B5.02 - VLT
®
is a registered Danfoss trademark
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