Use of EMC compliant cables
In order to comply with requirements for EMC immun-
ity of the control cables and EMC emissions from the
motor cables screened/armoured cables must be
used.
The ability of a cable to reduce the amount of ingoing
and outgoing radiation of electric noise depends on the
transfer impedance (Z
T
). The screen of a cable is nor-
mally designed to reduce the transfer of electric noise,
and a screen with a lower Z
T
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 looking at and assess-
ing the physical design of the cable.
Z
T
can be assessed on the basis of the following fac-
tors:
-
the contact resistance between the individual
screen conductors.
-
Screen coverage, i.e. the physical area of the
cable covered by the screen. Is often stated
as a percentage and should be no less than
85%.
-
The screen type, i.e. braided or twisted pat-
tern. A braided pattern or closed pipe is rec-
ommended.
44
MG.27.E2.02 - VLT is a registered Danfoss trademark