4.4.2 Electromagnetic compatibility (EMC)
The equipment shall not generate electromagnetic disturbances above levels that are appropriate for
its intended places of use. In addition, the
equipment shall have an adequate level of
immunity to electromagnetic disturbances so that it
can operate correctly in its intended environment.
NOTE 1 European standards EN 50081 and EN 50082-2 give
general EMC emission and immunity limits. Those requirements
are also under consideration by IEC TC 77 and ClSPR.
NOTE 2 Product standards (e.g. IEC 60439-1) may give more
specific EMC requirements.
Generated disturbances can be limited by:
— suppression at the source by using capacitors,
inductors, diodes, Zener diodes, varistors or
active devices, or a combination of these
components; or
— screening of the equipment in a bonded
electrically conductive enclosure to provide
segregation from other equipment.
Undesirable effects of electrostatic discharge,
radiated electromagnetic energy and mains borne
disturbances shall be avoided, for example by the
use of appropriate filters and time delays, a choice of
certain power levels, and the use of suitable wiring
types and practices.
Measures that can be used to reduce the effects of
disturbances on equipment include the following:
— connections of circuits to a reference potential:
each circuit is connected to a terminal on a
ground plane (chassis) (see Figure 4) that is
connected to earth using an insulated conductor
of large cross-sectional area (e.g. a minimum
area of 6 mm2 of type class 6 in accordance
with Table B.4);
— interconnections of conductive structural parts
of the equipment: conductive structural parts are
connected to a common point using conductors of
large cross-sectional area that are as short as is
possible. Conductive parts connected to the
equipment enclosure via sliding contacts or
hinges are also connected to that enclosure using
large section braided conductors (see also 8.3.3
and Figure 4);
— wiring practices: using electrostatic screens,
electromagnetic shields, twisted conductors, and
cable orientation (i.e. crossing cable runs at as
near to 90° as is practicable), or running the
conductors parallel to and as close as is
practicable to the ground-plane, to minimize the
disturbances from power cables to low level
control wiring; and
— separation of equipment: separating and/or
shielding sensitive equipment (e.g. units working
with pulses and/or at low signal levels) from
switching equipment (e.g. electromagnetic relays,
thyristors); separating low level signal wiring
from control and power cables.