3.3.9 EMC-Correct Electrical Installation
General points to be observed to ensure EMC-correct electrical installation.
-
Use only screened/armoured motor cables and screened/armoured control cables.
-
Connect the screen to earth at both ends.
-
Avoid installation with twisted screen ends (pigtails), since this ruins the screening effect at high frequencies. Use cable clamps instead.
-
Don't remove the cable screen between the cable clamp and the terminal.
3.3.10 Use of EMC Compliant Cables
In order to comply with requirements for EMC immunity 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 normally 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 often possible to estimate Z
T
by looking at and assessing the physical design of the cable.
Z
T
can be assessed on the basis of the following factors:
-
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 pattern. A braided pattern or closed pipe is recommended.
VLT
®
Decentral FCD 300 Design Guide
3 Installation
MG.90.S1.02 - VLT
®
is a registered Danfoss trademark
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