Control Wiring Connection; Access; Using Screened Control Cables; Earthing (Grounding) Of Screened Control Cables - Danfoss VLT AutomationDrive FC 300 Operating Instructions Manual

Installation

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 ). 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
®
VLT Automation Drive D-Frame
Operating Instructions
Illustration 2.24
2.5.3 Earthing (Grounding) of Screened
) value is
T
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
Illustration 2.25
1
2
Table 2.8
®
MG34U202 - VLT is a registered Danfoss trademark
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
Transfer impedance, Z
t
mOhm/m
10
10
10
10
10
1
10
10
10
0,01 0,1 1 10 100 MHz
Control Cables
PLC
PE PE
PE
1
2
2
Min. 16 mm
Equalizing cable
a
b
c
d
e
f
g
2 .
FC
PE
27
2 2