Access; Using Screened Control Cables; Grounding Of Screened Control Cables - Danfoss VLT AutomationDrive FC 302 Operating Instructions Manual

Installation

3.5.1 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).

3.5.2 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 ). The screen of a cable is normally
T
designed to reduce the transfer of electric noise; however,
a screen with a lower transfer impedance (Z
more effective than a screen with a higher transfer
impedance (Z ).
T
Transfer impedance (Z ) is rarely stated by cable manufac-
T
turers but it is often possible to estimate transfer
impedance (Z ) by assessing the physical design of the
T
cable.
Transfer impedance (Z ) can be assessed on the basis of
T
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
MG34U302
Operating Instructions
Transfer impedance, Z
mOhm/m
10
10
10
10
10
1
10
10
) value is 10
T
0,01
Illustration 3.24 Cable Screening Performance
3.5.3 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 ground potential between
the frequency converter and the PLC is different, electric
noise may occur that disturbs the entire system. Solve this
problem by fitting an equalizing cable next to the control
cable. Minimum cable cross section: 16 mm
1
2
Illustration 3.25 Correct Screening
Danfoss A/S © Rev. 2014-02-20 All rights reserved.
t
0,1 1 10 100 MHz
PLC
PE PE
<10 mm
PE PE
1
2
Min. 16 mm 2
Equalizing cable
a
b
3
c
d
e
f
g
2
.
FC
31
3