2.5 Control
Wiring
Connection
•
Isolate control wiring from high power
components in the frequency converter.
•
If the frequency converter is connected to a
thermistor, for PELV isolation, optional thermistor
control wiring must be reinforced/double
insulated. A 24 V DC supply voltage is
recommended.
2.5.1 Access
All terminals to the control cables are located underneath
the LCP on the inside of the frequency converter. To
access, open the door (IP21/54) or remove the front panel
(IP20).
2.5.2 Using Screened Control Cables
Danfoss recommends braided screened/armoured cables to
optimise 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
T
). The screen of a cable is normally
designed to reduce the transfer of electric noise; however,
a screen with a lower transfer impedance (Z
T
) value is
more effective than a screen with a higher transfer
impedance (Z
T
).
Transfer impedance (Z
T
) is rarely stated by cable manufac-
turers but it is often possible to estimate transfer
impedance (Z
T
) by assessing the physical design of the
cable.
Transfer impedance (Z
T
) can be assessed on the basis of
the following factors:
-
The conductibility of the screen material.
-
The contact resistance between the individual
screen conductors.
-
The screen coverage, i.e. the physical area of the
cable covered by the screen - often stated as a
percentage value.
-
Screen type, i.e. braided or twisted pattern.
a.
Aluminium-clad with copper wire.
b.
Twisted copper wire or armoured steel wire cable.
c.
Single-layer braided copper wire with varying
percentage screen coverage.
This is the typical Danfoss reference cable.
d.
Double-layer braided copper wire.
e.
Twin layer of braided copper wire with a
magnetic, screened/armoured intermediate layer.
f.
Cable that runs in copper tube or steel tube.
g.
Lead cable with 1.1 mm wall thickness.
Figure 2.12
Installation
VLT® Automation VT Drive FC 322 D-Frame Instruction Manual
MG21E122 - VLT® is a registered Danfoss trademark
2-11
2
2
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