![background image](http://html1.mh-extra.com/html/danfoss/vlt/vlt_design-manual_3509564027.webp)
will be necessary to break the screen to avoid current
loops.
Illustration 2.20 Situation that Generates Leakage Currents
If the screen is to be placed on a mounting plate for the
frequency converter, the mounting plate must be made of
metal, because the screen currents have to be conveyed
back to the unit. Moreover, ensure good electrical contact
from the mounting plate through the mounting screws to
the frequency converter chassis.
When unscreened cables are used, some emission
requirements are not complied with, although the
immunity requirements are observed.
In order to reduce the interference level from the entire
system (unit + installation), make motor and brake cables
as short as possible. Avoid placing cables with a sensitive
signal level alongside motor and brake cables. Radio
interference higher than 50 MHz (airborne) is especially
generated by the control electronics. See for more
information on EMC.
2.9.2 Emission Requirements
According to the EMC product standard for adjustable
speed frequency converters EN/IEC 61800-3:2004 the EMC
requirements depend on the intended use of the
frequency converter. Four categories are defined in the
EMC product standard. The definitions of the 4 categories
together with the requirements for mains supply voltage
conducted emissions are given in
Categ
ory
Definition
Conducted
emission
requirement
according to the
limits given in EN
55011
C1
Frequency converters installed in the
first environment (home and office)
with a supply voltage less than 1000
V.
Class B
C2
Frequency converters installed in the
first environment (home and office)
with a supply voltage less than 1000
V, which are neither plug-in nor
movable and are intended to be
installed and commissioned by a
professional.
Class A Group 1
C3
Frequency converters installed in the
second environment (industrial) with a
supply voltage lower than 1000 V.
Class A Group 2
C4
Frequency converters installed in the
second environment with a supply
voltage equal to or above 1000 V or
rated current equal to or above 400 A
or intended for use in complex
systems.
No limit line.
An EMC plan
should be made.
Table 2.9 Emission Requirements
When the generic emission standards are used the
frequency converters are required to comply with the
following limits
Introduction
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Refrigeration Drive Design Guide
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