Chapter 2
– Electromagnetically compatible installation of drives and drive systems
2-6
Using EMC compliant cables
In order to reduce electromagnetic emission caused by motor cables and to increase EMI immunity
for control cables, shielded cables have to be used. Using this shielding can reduce the interference
coupled into and out of the cable (please also refer to the previous chapter „Minimizing radiated
interference“). The effectiveness of the shielding heavily depends on the construction and the
material of the shielding. The screening effectiveness can be characterized by the so called transfer
impedance. This effectiveness or performance can be improved by keeping the transfer impedance
as low as possible. The transfer impedance is mainly affected by the following variables:
The cable covering, which is the cable area actually covered by the shielding. It is normally
indicated as a percentage value and should be at least 85%.
The shielding‘s design. Possible design alternatives are braided cables or shieldings made of
metal conduit. These two types should be preferred when shielding is to be implemented.
The contact (or transition) resistance between the individual stranded conductors of the
shielding. The performance of the shielding improves if this resistance is kept as low as
possible.
The following diagram shows the transfer impedance for various cable types. By comparing the
cables' individual design, the shielding effectiveness can be estimated and a suitable cable be
chosen.
10
-3
10
-2
10
-1
1
10
1
10
2
10
3
10
4
10
5
0,01
0,1
1
10
100
Kopplungsimpedanz
m /m
Frequenz
MHz
1
2
3
4
5
6
Aluminium-Ummantelung
mit Kupferdraht
Gewundener Kupferdraht oder
bewehrtes Stahldrahtkabel
Einlagiges Kupferdrahtgeflecht
mit schwankender prozentualer
Schirmabdeckung
Zweilagiges Kupferdrahtgeflecht
Zweilagiges Kupferdrahtgeflecht
mit magnetisch abgeschirmter
Zwischenlage
In Kupfer- oder Stahlrohr
geführtes Kabel
1
2
3
4
5
6
Bessere
Schirmwirkung
Improving
shielding
performance
Transfer impedance
Aluminum sheating with
copper wire
Meandering copper cable
or armoured steel wire
Single-layer copper wire
braid with varying
percentages of cable
covering
Double-layer copper wire
braid
Double-layer copper wire
braid with magnetically
screened intermediate layer
Cable running in conduit
made of copper or steel
