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
175ZA166.13
0,01
0,1
1
10
100 MHz
10ˉ2
10ˉ3
10ˉ1
1
101
102
104
103
105
a
b
c
d
e
f
g
The lo
w
er the Z the bett
er the cable scr
eening per
for
manc
e
Transfer impedance, Z
t
mOhm/m
Illustration 2.24
2.5.3 Earthing (Grounding) of Screened
Control Cables
Correct screening
The preferred method in most cases is to secure control
and serial communication cables with screening clamps
provided at both ends to ensure best possible high
frequency cable contact. If the earth (ground) potential
between the frequency converter and the PLC is different,
electric noise may occur that will disturb the entire system.
Solve this problem by fitting an equalizing cable next to
the control cable. Minimum cable cross section: 16 mm
2
.
1
2
PE
FC
PE
PLC
130BB922.11
PE
PE
Illustration 2.25
1
Min. 16 mm
2
2
Equalizing cable
Table 2.8
Installation
VLT
®
AQUA Drive D-Frame
Operating Instructions
MG21A202 - VLT
®
is a registered Danfoss trademark
27
2
2
