EMC and cable ducts
EMC
GoudaHolland
H1E-1-0
EMC
Contents
Page
Page
Introduction
H1E-1-2
Basics of EMC
H1E-1-3
Theory of electrics
Impedances
Magnetic field
Electric field
H1E-1-6
Annexes
H1E-1-25
Symbols and units of quantities
Dimensions and conversion of units
Abbreviations
References
Physical laws and effects
H1E-1-9
Installation of cables on cable ducts H1E-1-11
Installation of cables
Cable categories
Divide cabinets into zones
EMC of cables on cable ducts
H1E-1-15
Attenuation factors
H1E-1-15
Application of the EMC-theory
to cable ducts
Introduction
Cabinets
CM-currents
Connections of low impedance
Shielding
Transfer impedance
Holes and perforations
H1E-1-16
Selection of cable duct types in
accordance with EMC-requirements
UNIC
RESIST
CRAFTY
STREAMLINE
TRAY
LOCK
TANDEM
H1E-1-28
H1E-1-28
H1E-1-29
H1E-1-29
H1E-1-30
H1E-1-31
H1E-1-31
Index
H1E-1-32
H1E-1-26
Application of cable ducts
H1E-1-21
Cable laying on cable ducts
Application of cable ladders and flat
bottom cable ducts
Separation strips
Cable ladders with additional plates
Wire mesh trays
Wall channels
Conclusion
H1E-1-24
All rights reserved. Nothing from this edition may be
multiplied, stored in an automised database or be made
public in any form, or in any way, neither electronical,
mechanical, by fotocopy, shots, nor in any other way, without
previous permission in writing of the publisher.
H1E-1-1
All type designations, drawings and constructions of models
and components mentioned in this documentation are
covered by the copyright of Gouda Holland BV
Gouda Holland
EMC
An increasing number of customers continually
inquires about the influences of cable ducts on
ElectroMagnetic Compatibility (EMC).
ElectroMagnetic Compatibility (EMC) is a field of
electrics and electronics that is gaining attention.
This applies not only to the equipment level, but
also to the project level, for instance for systems
and installations.
This is due to several reasons. The electronic
equipment applied, such as PC's (Personal
Computers) and PLC's (Programmable Logic
Controllers), has an increasing susceptibility to
disturbances. On the other hand there is an
increasing use of sources generating
disturbances, such as e.g. frequency convertors
for motors.
Also the equipment is packed more densely than
before. This results in a closer location of
disturbance sources and susceptible equipment.
Various investigations in the field of EMC have
proved, that the design and construction of cable
ducts play a significant role in the achievement of
the EMC of installations.
As a specialist in the field of industrial cable ducts,
Gouda Holland decided to inform their customers
about the newest trends in the field of EMC.
Therefore Gouda Holland has asked
Mr. D.S.J.Schuuring M.Sc. of PEMCO Physical and
EMC Consultancy at Delden to research the
effects of the several types of cable ducts on the
EMC of installations.
The results of this research are discussed in this
brochure which gives practical advice for the
application of cable ducts in the electromagnetic
environment.
The EM-environment outside the installation can
also create disturbances for example through the
increasing use of wireless communication (e.g.
portable telephones).
Therefore it is necessary to apply EMC-measures
to protect installations against unwanted effects
caused by electromagnetic disturbances.
These EMC-measures are also necessary to make
the installation meet the European Union (EU)
regulations, introduced from 1st January 1996,
and laid down in the EMC-directive.
It is because of these EMC-requirements that the
construction and installation industry makes extra
costs to ensure that EMC-measures are
implemented. This means applying the EMCrequirements to the electrical parts of the
installation. But also the mechanical parts can play
an important role in improving the earthing system.
This can be achieved by connecting metal
mechanical parts, such as cable ducts which run
through large parts of an installation. Given their
importance, it is vital that the cable ducts meet the
EMC-regulations.
H1E-1-2
EMC
Introduction
Basics of EMC
EMC
Basic knowledge
Introduction
Before explaining the EMC-measures to be
applied to cable ducts, a brief outline of some of
the definitions and theories in the field of EMC will
be given.
Basic knowledge of EMC is necessary in order to
understand the effects of its measures. Designers
and constructors often acquire their knowledge
through practical experience of solving
interference problems. But when one has a
theoretical understanding of the EMC-measures,
they can be implemented much more effectively.
Definitions
Definitions used, are those which are given in the
standards of the IEC (International Electrotechnical Commission).
These definitions apply to 'devices, equipment and
systems', but can also be used for installations.
Installations
When systems are mentioned in the definitions or
the text installations will be included.
This brochure deals mainly with installations of
industrial projects.
EMC
The definition of ElectroMagnetic Compatibility
(EMC) is:
'The ability of a device, equipment or system to
function satisfactorily in its ElectroMagnetic (EM)
environment without introducing intolerable
electromagnetic disturbances to anything in that
environment'.
From this definition follows:
- equipment within a system shall not disturb
each other. This is called 'Intra system EMC'.
- the system shall not be disturbed by equipment
or systems in the EM-environment
- the system shall not disturb equipment or
systems in the EM-environment.
The last two statements are called 'Inter System
EMC'.
Interference
The definition of ElectroMagnetic Interference
(EMI) is:
'Degradation of performance of an equipment, a
transmission channel or a system caused by an
electromagnetic disturbance'.
Instead of 'electromagnetic interference' often
simple 'interference' is used.
H1E-1-3
Difference between EMI and EMC
EMI is the interference of one equipment or
system. EMC is the compatibility between
equipment or systems.
Disturbances
The definition of electromagnetic disturbance is:
'Any electromagnetic phenomenon which may
decrease the performance of a device, equipment
or system'.
Disturbances may exist of:
- conducted disturbing signals
- radiated disturbing signals or radiation
EM-environment
The definition of ElectroMagnetic (EM)
environment is: 'The totality of electromagnetic
phenomena existing at the given location'.
The electromagnetic phenomena at the location of
the installation may exist of:
- conducted disturbances of other installations
via power cables or interconnection cables
- radiated disturbances, e.g. of transmitters for
communication, radar transmitters or transmitters of industrial processes for heating,
gluing, drying etc.
- lightning. Protection against the effects of
lightning will only be treated briefly.
The installation itself may also generate disturbances in the EM-environment, which may cause
interference in other parts of the installation.
Emission, susceptibility and immunity
Emission
The definition of electromagnetic emission is:
'The phenomenon by which electromagnetic
energy emanates from a source'.
The 'source' is also called 'emittor'.
Susceptibility
The definition of electromagnetic susceptibility is:
'The inability of a device, equipment or system to
perform without degradation in the presence of an
electromagnetic disturbance'.
The device which is interfered is called 'susceptor'
or 'victim'.
Immunity
The definition of immunity to a disturbance is:
'The ability of a device, equipment or system to
perform without degradation in the presence of an
Basics of EMC
electromagnetic disturbance'.
Immunity is the opposite of susceptibility.
The disturbances from a source and to a victim
are shown in fig. 1.
IMMUNITY OR
SUSCEPTIBILITY
radiated
disturbances
EMISSION
radiated
disturbances
conducted
disturbances
source
Figure 1
conducted
disturbances
victim
Frequency ranges
The frequency range of electromagnetic disturbances is large. It starts at the supply frequency
(50 Hz) and ranges up to tens of gigahertz. In the
EMC-standards for measurements the frequency
range is divided in a number of subranges. The
frequency ranges as mentioned in the so called
'generic standards' are shown in fig. 4 as solid
lines. In product standards other frequency ranges
may be present and also in standards under
consideration; some of these ranges are shown in
fig.4 with dotted lines.
Frequency in Hz
Emission, susceptibility and immunity
10
Basic form of an interference problem
In each interference problem three elements are
present (three-element-model; fig. 2):
- source :
device emanating disturbances
- victim :
device which is interfered
- coupling channel : the way by which the
disturbance is transported
100
1k
10k 100k
1M
10M 100M 1G 10G 100G
standards published
Emission
standards to be published
harmonics
(0 k)
2k
conducted
9k
150 k
30 M
radiated
Immunity
harmonics
30 M
source
(emittor)
Figure 2
coupling
channel
victim
(susceptor)
RADIATION
EMITTING
DEVICE
SUSCEPTIBLE
DEVICE
CONDUCTION
COUPLING
capacitive
inductive
common impedance
Coupling channels for disturbances
1G
18 G
2k
conducted
150 k
The three elements of an interference problem
Coupling channels
Coupling channels for the disturbances from the
source to the victim are (fig. 3):
- conduction via:
- power cables
- interconnection cables
- earthing system
- coupling:
- via common impedancies
- capacitive coupling
- inductive coupling
- radiation
Figure 3
(0 k)
I
50 k
Figure 4
80 M
radiated
I
80 M 1 G
1,89 G
Frequency ranges of emission and immunity tests
The most important frequency ranges are:
Emission
Conducted disturbances
- frequency range: 0 - 2 kHz
Supply frequencies and harmonics
- frequency range: 150 kHz - 30 MHz
Disturbances generated by electrical and
electronic circuits, switch actions etc.
Radiation
- frequency range: 30 MHz 1 GHz
Electric fields of electronic circuits, transmitters
etc.
Immunity (frequency domain)
Conducted disturbances
- frequency range: 150 kHz - 80 MHz
Radiation
- frequency range: 50 Hz (magnetic field)
- frequency range: 80 MHz - 1 GHz, 1,89 GHz
(electric fields)
H1E-1-4
EMC
Basic knowledge
Basics of EMC
EMC
Types of disturbing signals
Next to the immunity tests in the frequency domain
there are tests in the time domain; these are:
Immunity (time domain)
- ESD
(ESD - electrostatic discharge)
- EFT/burst
(EFT - electrical fast transients)
- Surge
- Voltage variations, dips and interruptions
Types of disturbing signals
As already mentioned disturbances can be divided
into some classes:
Conducted disturbing signals
Conducted disturbing signals are divided into:
Disturbing voltage
The disturbing voltage can be divided into:
- differential mode (DM) voltage (fig. 5a and 6)
This is the voltage between lines of a circuit.
- common-mode (CM) voltage (fig. 5b and 6)
This is the voltage between all lines of a cable and
earth.
The DM voltage is important in the low frequency
range, frequencies below 10 Mhz. The CM voltage
is important above the frequency of 10 MHz.
DIFFERENTIAL MODE (DM)
fase 1
COMMON-MODE (CM)
fase 2
fase 1
fase 2
UDM
UCM
earth system
Figure 5
earth system
Disturbing voltages
Disturbing current
The disturbing current appears as:
- DM current through the lines of a circuit
- CM current through a cable and a return. The
return usually is the earthing system (fig. 6)
device 1
shielded cable
device 2
UDM
I CM
UCM
earthing system
Figure 6
H1E-1-5
Common-mode disturbing signals
Disturbing power
The disturbing power is the product of the
disturbing voltage and the disturbing current in a
circuit. Disturbing power is sometimes used for
CM signals above the frequency of 30 MHz.
Disturbing radiation
Disturbing radiation can be divided into:
Magnetic induction and magnetic fields:
Magnetic induction B is used to expres magnetic
fields at short distances of the source. Magnetic
fields or H-fields mainly exist in the low frequency
range (below 30 MHz).
Electric fields and electromagnetic fields:
Electric fields or E-fields are mainly disturbing in
the higher frequency range (above 1 MHz). At high
frequencies, that means above 0,3 GHz, the fields
become electromagnetic.
Pulses
Next to the signals in the 'frequency domain', as
mentioned above, disturbing signals in the 'time
domain' may be present in the form of pulses,
sometimes called 'transients'. Types of pulses
important in the EMC are defined in the EMCstandards for measuring the immunity (IEC 10004-series).
Theory of electrics
Impedances
impedance
EMC
Introduction
Parts of the theory of electrics are refreshed briefly
for a better understanding of the EMC-phenomena.
Only subjects of direct importance for cable laying
in installations are treated.
An overview of dimensions and units of quantities
used in this paragraph is given in the annex.
Some properties and physical constants of metals
are given in Table 1.
Z=wL
Z(W)
R
frequency
Resistance of a wire and a strip
The ohmic resistance of a wire or strip is calculated
with the formula:
R = r. l / A
where: R
r
l
A
- resistance in W
- specific resistivity of metal in W m
- length of wire or strip in m
- cross section of wire or strip in m²
f(Hz)
Figure 7
and (thickness) c, is compared with a round wire
with diameter d.
d
Impedance of a wire
The impedance of a wire in the low frequency
range is determined by the resistance. However
each conductor also has a self-inductance which
becomes noticeable at higher frequencies. The
value of the inductance is determined by the
dimension and the form of the cross section. A
rule of thumb for the self-inductance of a wire is:
L = 1 µH/m
For the impedance due to the self-inductance the
formula applies:
Z=2pf.L
where: Z - impedance in W
f - frequency in Hz
L - self-inductance in H
Above the frequency of a few hundreds of hertz
(depending on the dimensions of the conductor)
the value of the impedance due to the selfinductance becomes higher than the value of the
resistance (fig. 7). Above this frequency the
impedance of the wire increases with the
frequency.
Impedance of a strip
In general a strip has a lower self-inductance than
a wire. A strip with dimensions (fig. 8) (width) b
Impedance of a conductor as
a function of the frequency
c
b
Figure 8
Self-inductance of a round wire
is higher than of a strip
Theoretically an approximation for the ratio of the
self-inductance of the wire to that of the strip is a
factor: 2d/(b + c). From this formula it follows that
the broader the strip the lower the self-inductance.
Another conclusion is, that the thickness of broad
strips is not important. In practice the thickness is
mainly determined by the mechanical strength.
Besides the lower self-inductance, the strip has
the advantage of the skin effect. Due to this effect
at high frequencies the impedance of a strip is
lower than the impedance of a wire, which will be
discussed later on.
The impedance of a conductor can be kept
relatively low by the use of broad strips. This effect
can be brought into practice by using cable ducts
as conductors for the earthing system. Keeping
the lenght as short as possible also reduces the
impedance.
H1E-1-6
Theory of electrics
EMC
Magnetic field
Magnetic field strength of a wire
The magnetic field strength H generated by a wire
carrying a current I is according to the law of Biot
and Savart given by the formula (fig. 9):
H=I/2pr
where: H - magnetic field strength in A/m
I - current in A
r - distance to the wire in m
I
distance between the wires is, the smaller the
remaining field strength is. The magnetic field
strength of the two wires together decreases with
the square of the distance to the measuring point.
This method of reduction of field strength due to
two conductors with currents in opposite
directions is applied in laying cables close to cable
ducts in case of common-mode currents flowing
through the cable shield with a return current in the
cable duct.
Magnetic field strength of a circular loop
The magnetic field strength H of a loop of circular
shape with radius r in which a current I is
flowing is in the centre of the loop (fig. 11):
r
H=I/2r
H= I /2 pr r
Figure 9
where: H - magnetic field strength in A/m
I - current in A
r - radius of the loop in m
Magnetic field of a wire
H= I / 2 r
Magnetic field strength of two parallel wires
The magnetic field strength of two parallel wires at
a distance d in which currents flow of the same
amplitude, but in opposite directions (fig. 10) is
given by:
H = I . d / 2 p r2
where: H
d
I
r
r
I
Figure 11
- magnetic field strength in A/m
- distance between the wires in m
- current in A
- distance to the wire in m
I1
Magnetic field of a circular loop
Outside the loop the field strength decreases with
increasing distance to the loop. On a certain
distance of the loop, e.g. in the point P at a
distance d of the centre, the field strength has
decreased with the third power of the distance to
the centre (fig. 12).
d
P
H
d
H1
H2
I2
I
Figure 10
Magnetic field of two parallel wires
Because the currents in the wires flow in opposite
directions, the generated magnetic fields
compensate each other partly. The smaller the
H1E-1-7
Figure 12
Decreasing magnetic field strength as a
function of the distance to the loop
Magnetic field
Electric field
Magnetic field strength of a non-circular loop
For the special case of a non-circular loop the
formula for the magnetic field strength of two
parallel wires can be used.
Short antennas, i.e. antennas with a length smaller
than a tenth of a wavelength, have an effectivity
proportional to the ratio length to wavelength.
A conductor with one open end functions as a rod
antenna. The antenna works effectively when the
length is a quarter of a wavelength or in general at
lengths:
Magnetic induction
For the calculation of the magnetic induction the
following formula can be applied:
B = µ . H = µo . µr . H
where: B - magnetic induction in T
µ - magnetic permeability in H/m
µo - magnetic permeability of vacuum
(4 p 10-7H/m)
µr - relative magnetic permeability
H - magnetic field strength in A/m
Magnetic flux
The formula for the calculation of the magnetic flux
is:
l = ¼ l (1 + 2n)
with n = 0, 1, 2, 3, ...
A conductor which is connected at both ends
functions effectively as a antenna when the length
is a half wavelength or in general at lengths:
l=½
l .n
with n = 1, 2, 3, ...
Example:
Cable shields function as effective antennas. They
are connected at both ends to the earthing
system. Suppose a disturbing voltage is present
with a frequency: f = 10 MHz. The wave length of
that signal is:
l = c / f = 3.108 / 10.106 = 30 m
F=B.A=µ.A.H
where: F
A
H
- magnetic flux in Wb
- area of the loop in m2
- magnetic field strength in A/m
The described formulas are used to calculate the
magnetic field strength, the magnetic induction or
the magnetic flux of loops in the earthing system,
e.g. formed by a cable shield and a cable duct.
Electric field
Behaviour of a conductor as antenna
A conductor acts as an electric antenna.
A voltage on a conductor will generate an electric
field. Besides a conductor a second element is
necessary. Usually the other element, to which the
voltage is refered, is the earthing system. The
effectivity of a conductor as antenna depends on
the ratio wavelength of the signal to the length of
the conductor. The wavelength of the signal is
calculated from the frequency with the formula:
l =c/f
where: l
f
c
- wavelength in m
- frequency in Hz
- speed of light (3.108 m/s)
The cable will function as an effective antenna for
the following lengths:
l = 15 m, 30 m, 45 m etc.
Reversely, when a cable has a certain length, the
frequencies at which it will act as an effective
antenna can be calculated.
Actually the wavelengths in the cables will be
smaller, because the transmission velocity of a
signal in a metal is smaller than the speed of light.
Electric field strength
The electric field strength E at a distance r of a
source, of which the power P is known, can be
calculated by an approximation formula which is:
E=7ÖP/r
where: E - electric field strength in V/m
P - power of the transmitter in W
r
- distance to the source in m
Theoretically this formula is valid for distances
from the source that are larger than 1/6 of a
wavelength. In practice the formula can be used
even for smaller distances.
H1E-1-8
EMC
Theory of electrics
EMC
Physical laws and effects
Kirchhoff's law
Kirchhoff's law for currents says:
The algebraic sum of the currents flowing towards
any point is zero (fig. 13a). For this summation the
direction of the currents must be taken into
account. From this law it follows, that currents can
only flow in loops (fig. 13b).
I1
I2
I1
I2
I3
SI = 0
SI = 0
I1 +I2 - I3 = 0
a. sum of currents in
node is zero
Figure 13
I1 - I2 = 0
b. current flows in a loop
Kirchhoff's law for currents
Lenz's law
Lenz's law says:
For currents induced by motion in a magnetic field,
the induced currents have such a direction that
their reaction tends to oppose the motion which
produces them.
The same is valid for alternating currents, where
the magnetic field changes due to the alternation.
From this law it can be derived, that in circuits the
return current takes a path so that the magnetic
flux is as small as possible.
As already given the formula for the magnetic flux
is:
F=µAH
where: F
µ
A
H
- magnetic flux in Wb
- magnetic permeability in H/m
- area of a loop in m2
- magnetic field strength in A/m
The magnetic flux is frequency dependant, as is
evident from the dimension: Wb = V . s = V/Hz.
The magnetic flux can be kept small by keeping
the area of the loop (A) small. This can be
achieved when the return current is able to flow
through a path close to the original current.
This occurs, when a common-mode current in a
cable shield is able to flow back through a
H1E-1-9
conducting plane below the cable. The current will
flow as close as possible to the current in the
shield. The cable duct acts as the conducting
plane.
Experiment
This phenomenon can be shown in an experiment.
In a U-shaped metal tube a wire is installed
(fig. 14). One end of the wire is connected to one
end of the tube. The other end of the wire is via a
current source connected to the other end of the
tube. The ends of the tube are also connected via
a heavy bar.
At low frequencies most of the return current will
flow through the bar. With increasing frequency the
largest part of the return current will flow through
the tube. At the supply frequency (50 Hz) already
90 % of the current will flow through the tube
(IB = 10 IA).
IB
IA
A
IA < IB
B
I
metal tube with current
carrying wire inside
current source
Figure 14
Experiment to show the effect of Lenz's law
Skin effect
The skin effect is the electromagnetic effect, that in
a conductor carrying an alternating current, the
current density will be greater at the surface of the
conductor than in the centre. At sufficiently high
frequencies the current is practically confined to
the skin layer of the conductor. The depth at which
the current is decreased to 1/e of the value at the
surface is called the skin depth (e - base of the
natural logarithm; e = 2,718...).
For calculations normally it is assumed, that at a
depth of three skin depth the current is negligible
small.
The formula for the calculation of the skin depth is:
d = 1 / Ö {p . f . s . µ} = 503 / Ö {f . s . µr }
where: d
f
s
µr
- skin depth in m
- frequency in Hz
- specific conductivity in S/m
- relative permeability of the metal
Remark:
The specific conductivity is the reciprocal of the
specific resistivity r , thus s = 1 / r (r in W . m).
From the formula follows:
- the higher the frequency the thinner the skin
layer
- the higher the specific conductivity, thus the
lower the specific resistivity, the thinner the skin
layer
- for a magnetizible metal, e.g. iron or steel, the mr
is higher than one and the skin layer is thinner.
For some metals used for the construction of
cable ducts the skin depths are given (Table 1).
Where for some metals a range of values is given,
the skin depth is calculated from the mean value.
Table 1
To reduce the influence of the skin effect on
current carrying conductors it is advantageous to
use strips instead of round wires. This is shown in
fig. 15 for a wire and a strip of identical cross
section. The shaded area of the strip is larger than
that of the wire.
3d
3d
a. round wire
Figure 15
b. strip
Skin effect
A cable duct consists of broad metal strips, which
is advantageous with respect to the skin effect.
Stainless steel is more advantageous in conducting high frequency currents because of the large
skin depth. Steel is more advantageous in
shielding magnetic fields because of the high
relative magnetic permeablity. In practice both
steel and stainless steel proved to be satisfactory.
Skin depths for some metals
material
specific
resistivity
relative
permeability
skin depth
frequency
f = 1 MHz
3
µr
in 10 -9
.m
Copper
Aluminum
Steel
18
28
110
Stainless
steel
720-800
(760)
1
1
500-1000
(750)
1,0
in m
in mm
in mm
0,067/ f
0,084/ f
0,006/ f
67/ f
84/ f
0,20
0,25
6/ f
0,02
0,44/ f
440/ f
1,3
H1E-1-10
EMC
Physical laws and effects
EMC
Installation of cables on
cable ducts
Installation of cables
The way the cable lay-out of an installation is
designed is important in order to achieve EMC.
The EM-environment also plays a role. In a noisy
EM-environment the laying of sensitive cables
requires extra attention. The same is true for noisy
cables in a quiet EM-environment.
The cable types used are also important. It is
assumed that where necessary, shielded cables
are used. The cable shields have to be connected
at both ends. In this way currents are able to flow
in the cable shields, which will reduce the
influence of the fields. This is the only way to
shield high frequency fields.
Normally shields made of copper are used. When
only low attenuation values are required, also steel
armours can be used as cable shield.
In exceptional cases, cable shields have to be
connected at one end only. This happens when
low frequency analog signals are transported by
the cables. In this situation two insulated shields
have to be used. The inner shield is bonded at
only one end to reduce the influence on the
signals by low frequency currents which may flow
in the cable shield. The outer cable shield is
bonded at both ends to shield high frequency
fields.
In practice often disturbing electrical fields are
present in the megahertz range, e.g. in tens of
MHz. The wavelengths belonging to these
frequencies are tens of meters. In installations,
often cables of these lengths are present and will
act as antennas.
Cabinets and consoles usually have dimensions of
meters. This means they are able to radiate or pick
up fields in the frequency range of hundreds of
megahertz.
In installations cables will usually be the main
radiators of (fig. 16) and receivers (fig. 17) from
disturbing fields.
Remark: Also the signals to be transported by
cables may be disturbing for circuits, connected to
lines in other cables. This is for example the case
for supply currents and cables with pulses.
radiated disturbances
from cabinet
connection cables
source
(emitting
device)
earth
connection
Figure 16
H1E-1-11
radiated disturbances
from cables
power cable
conducted
disturbances
Emission of disturbing signals by a system
Cables as emittors:
Cables are able to transport signals and
disturbances through the installation over large
distances. During the transport the following
phenomena may take place:
- disturbing signals of a cable may couple into
parallel running cables
- cables may radiate electric fields in the
frequencies of the disturbing signals
- cables may radiate magnetic fields when they
are part of a loop
- cables may radiate magnetic fields when they
are carrying high currents. This is mainly the
case for currents in the supply frequency and
their harmonics
- cables may couple disturbing signals directly
into susceptible equipment.
radiated disturbances
to cabinet
connection cables
victim
(susceptible
device)
earth
connection
Figure 17
radiated disturbances
to cables
power cable
conducted
disturbances
Coupling of disturbing signals into a system
Cables as susceptors:
In the same way that cables emit disturbances,
cables may also pick up disturbances:
- a cable may pick up disturbing signals of a cable
running in parallel
- cables may pick up electric fields
- cables may pick up magnetic fields when they
are part of a loop
- cables may pick up magnetic fields of cables
carrying high currents. This is mainly the case for
currents in the supply frequency and their
harmonics
- cables may directly pick up disturbing signals
from equipment generating these signals.
When these cables are connected to susceptible
circuits, interference may occur.
These effects can be diminished in several ways,
e.g. by:
- dividing cables into cable categories
- separation between cables of the several cable
categories
- decreasing the antenna behaviour of cables by:
- cable laying on a conducting earthed plane
- shielding, e.g. by cable ducts
- prevention of the formation of loops in cables.
Cable categories
Cables can be divided into categories depending
on the signals they are transporting. This division
is made on the bases of signal levels and
frequencies, or for pulses on the bases of
amplitude and the pulse rise and decay times.
In practice often a division into three categories is
made:
- indifferent cables
Cables of this category contain less jamming
and less sensitive signals. Examples are power
cables.
- sensitive cables
This category contains instrumentation and data
cables.
- jamming or noisy cables
This category contains control cables as e.g.
motor cables of frequency converters.
In special cases more categories can be added,
such as:
- very sensitive cables
Cables with very low signals as from sensors.
- strong jamming cables
Cables with high power signals, high frequencies
or high level pulses.
Remark:
An equipment supplier may prescribe to lay all the
cables of a system together. In that case it is
recommended to lay these cables as a separate
category.
Table 2
Measures to be taken on cable ducts carrying
different cable categories in several EM-environments
Next to the use of open cable ducts, in some
cases covered cable ducts can be used. This
depends mainly on the EM-environment in
combination with the sensitivity of the cables.
In a strong jamming EM-environment the sensitive
cables shall be laid in cable ducts of solid metal;
the very sensitive cables shall be laid in cable
ducts with covers.
In an EM-environment which contains sensitive
equipment the jamming cables have to be given
extra attention.
This is shown in Table 2. This table will be
discussed in extend below when discussing the
types of cable ducts.
Divide cabinets into zones
Electrical and electronic parts and components
can, analogous to cable categories, be divided
into zones of different disturbance behaviour.
Some EM-zones are:
- EM-zone 2 for susceptible parts
- EM-zone 3 for parts which are indifferent or
neutral
- EM-zone 4 for disturbing parts
It is recommended to install parts belonging to a
certain EM-zone into a separate cabinet and keep
some distance between cabinets of different EMzones (fig. 18).
EM-zone 4
Fig. 18
Cable category very sensitive normal strong jamming
X
E
EE
sensitive
X
X
E
indifferent
X
X
X
X - normal
jamming
E
X
X
E - extra
strong jamming
EE
E
X
EE - double extra
Measures
The cables are laid in groups of one category. The
distance between the groups of successive
categories laid on the same cable duct shall be:
- minimum 0,2 m for cable categories on cable
ladders
- minimum 0,15 m for cable categories on cable
ducts with a solid or perforated bottom.
Also a distance of 10 times the diameter of the
thickest cable is sufficient.
The distance between open cable ducts shall be
at least 0,15 m.
EM-zone 3
EM-zone 2
kabel duct
EM-environment
very sensitive
EM-zone 3
Cabinets with circuits of different levels of
disturbances shall be placed into shielding compartment, mounted at some separation distance
If all electrical and electronic parts are mounted
into a single cabinet, parts belonging to one EMzone shall be mounted into a shielded compartment and some distance shall be present between
compartments of different EM-zones (fig.19).
zone 2
susceptible
wiring and cabling
cable connection plate
zone 3
neutral
zone 3
neutral
Fig. 19 Inside cabinets circuits
of different levels of
disturbances shall be
placed into shielding
compartment,
mounted at some
separation distance
zone 4
disturbing
4
3
2
H1E-1-12
EMC
Installation of cables on
cable ducts
Installation of cables on
cable ducts
EMC
Behaviour of cables as antennas
Electric antenna
The behaviour of cables as antennas can be
decreased by laying the cables close to a
conducting surface, e.g. the earthing system. The
capacity of the cables to earth becomes so large,
that their effectivity as a radiator diminishes. Thus
the generation of electric fields will also diminish.
Electric fields arise when voltages are present in
the cables. This may be the case on the lines of
non-shielded cables. In a shielded cable, when the
shield is connected at both ends to earth, hardly
any voltages will occur and thus only very weak
electric fields will be generated. This is only true
when the cable length is much smaller then the
wavelength of the disturbing signal. For cable
lengths resembling half, or multiples of a half,
wavelengths of the disturbing signals resonances
may occur and high electric field strengths may be
generated.
Loop
Suppose the cable shield is carrying a disturbing
current, e.g. a CM-current, of which the return
current flows through the earthing system
(fig. 20a). The current in the loop generates a
magnetic field. Reversely a magnetic field is able
to induce a current into the loop.
The loop in which the current is flowing can be
made smaller by introducing an earth conductor
close to the cable (fig. 20b); this is called a PEC
(Parallel Earth Conductor).
A cable duct can also form a PEC (fig. 20c). In that
case the cable duct shall form a continuous
conducting path over the whole length.
cables
Ist =I CM
large loop
earthing system
Figure. 20a
Loop with CM-current
Ist
I CM
small loop
cables
parallel earth
conductor (PEC)
earthing system
Figure 20b
H1E-1-13
Diminishing of the loop by a PEC (Parallel Earth
Conductor)
Ist
cables
I CM
Figure 20c
cable duct as part
of earthing system
Diminishing of the loop by a cable duct
Single wire or cable
The magnetic field strength generated by a current
in a wire or cable can be decreased by laying the
return wire close to the current carrying wire.
Therefore each circuit shall have its own return.
Strong currents appear mainly in power cables,
especially as the mains network is constructed as
bars. Decoupling with other cables can be
achieved by enlarging the distance. Shielding of
low-frequency magnetic fields is difficult.
Prevention of field generation
Besides the reduction of the generation of fields by
laying the cables on conducting surfaces, some
other measures will be discussed.
Electric field strength generated by cables can be
decreased by the shielding of the cables or by
using closed cable ducts, e.g. cable ducts with a
cover.
Magnetic field strength due to CM-currents in
cables can be reduced by reducing the area of the
loop in which the currents are flowing. This can
often be reached by changing connections in the
earthing system. Before improvements can be
introduced, measurements are necessary to locate
the paths of the currents.
Results of the introduction of conducting
surfaces
Results of the introduction of conducting surfaces
beneath cables are:
Electric field:
- electric field strength reduces, due to the
reduction of the effectivity as antennas
- coupling between parallel running cables
decreases. The reduction is proportional to the
reduction of the ratio capacitance to parallel
cable and capacitance to conducting surface.
Magnetic field:
- magnetic field strength reduces, due to
reduction of the loop in which currents flow as a
result of the closer neighbourhood of a
conducting surface
- coupling between parallel running cables
decreases, due to the fact that of both cables
the area of the loop is reduced as a result of the
closer neighbourhood of a conducting plane.
Installation of cables on
cable ducts
Behaviour of cables as antennas
A
A
A
R
P
flat
R - best:
A - good:
P - poor:
L-shape
P
P
R
A
EMC
Shielding by metal plates
Metal plates and beams show a shielding effect on
cables routed on them (fig. 21). On a strip the
cables shall be laid in the middle of the plate. This
gives a moderate shielding effect. On a L-shaped
beam the cables shall be laid in the corner; this
gives a good shielding attenuation. A canal, such
as present at a H-shaped beam, gives the best
shielding attenuation, when the cables are laid into
the corners.
R
H-shape
recommended
acceptible
not recommended
Fig. 21 Shielding behaviour of plates and beams
The deeper the canal, the higher the attenuation.
The highest shielding attenuation is attained when
using canals with a cover or pipes (fig. 22).
cable duct with
cover
pipe
Figure. 22
Highest shielding attenuation is gained with
closed constructions
H1E-1-14
EMC
Earthing
system
Attenuation
factors
Earthing system
The construction of the earthing system of an
installation needs a lot of attention. This is
because the proper working of several EMCmeasures, such as shielding, filtering, protection
measures against the generation of overvoltage
and protection against lightning, depends on a
low-impedance earthing system. The ideal
earthing system is a plane. In installations this
cannot be realised and an earth grid is used.
Attenuation factors
In the literature often attenuation factors or
attenuation values in dB are given. For that reason
the way attenuation is calculated will be
mentioned.
The attenuation factor of an EMC-measure is the
ratio of the original signal to the attenuated signal.
As an example the attenuation of the electric field
strength by a shielding wall will be explained
(fig. 24).
The attenuation factor S of a shielding device is
the ratio of the incoming field strength Ein to the
outgoing field strength Eout, so:
The earthing system shall include all constructional
metal parts. Such metal parts are e.g. steel
beams, plates, ironwork of reinforced concrete,
frames and also the cable ducts (fig. 23). These
metal parts shall be bonded to the earthing
system at least every 10 m. with a low impedance.
Besides the EMC earthing system the safety earth
is present, this is the Protective Earth (PE).
Often conductors of the PE, e.g. in the form of
bars with dimensions 5 mm x 20 mm, are laid
parallel to the cable ducts. This safety system is
connected to the EMC earthing system at many
places.
earthing
system
S = Ein / Eout
where: S = attenuation factor
Ein = incoming electric field strength in
V/m
Eout = electric field strength after
attenuation in V/m
For the dB-value of the shielding attenuation
follows :
A = 20 log (Ein / Eout )
where: A= attenuation in dB
Numerical example:
When the signal is attenuated by a factor 10, so :
steel
construction
Ein / Eout = 10
cable duct
then the attenuation value is :
A = 20 log 10 = 20 dB
In the same way an attenuation with a factor 100
gives an attenuation value of 40 dB, a factor 1000
a value of of 60 dB, and so on.
From this example it becomes clear, that relative
low attenuation values already give a large
decrease signal amplitude. In many cases an
attenuation of 20 - 30 suffices, reducing a field
strength of E = 100 V/m to E = 3 - 10 V/m.
shielding wall
ring earth
earth electrode
E in
Figure 23
EMC-earthing system of building (schematic)
From an EMC point of view it is not necessary to
ground the EMC earth system but for other
reasons this is practiced; because the system can
also be used for, or connected with the safety
earth and the lightning protection installation.
H1E-1-15
E uit
Figure 24
Attenuation of an electric field by a shielding wall
Introduction
The proper construction of cable ducts can
improve the EMC of a system. This is only valid for
metal cable ducts which form part of the earthing
system. These cable ducts:
- improve the earthing system by reducing the
impedance of it
- reduce the coupling between cables
- reduce radiation of electric and magnetic fields
- reduce the pick up of electric and magnetic
fields.
In order to perform these functions the
construction of the cable ducts shall fulfil specific
requirements, which are discussed below.
Some of these requirements are also laid down in
the standard IEC 61000-5-2 (Ref. 3).
as the general term for all kind of enclosures as
consoles, panels, junction boxes, equipment racks
etc. It is assumed that the cabinets are made of
metal and show a certain amount of shielding
attenuation.
Cabinets
Requirements for cable ducts between cabinets
will be discussed. The term 'cabinets' will be used
cabinet 2
cabinet 1
strip A
Figure 25
Cable ducts form a continuous earthing system from cabinet to cabinet
H1E-1-16
EMC
Application of the EMC-theory
to cable ducts
Application of the EMC-theory
to cable ducts
EMC
Cable ducts
CM-currents
Cable ducts are used to conduct the return
currents of CM-currents flowing through the
cables, especially through the cable shields.
These return currents shall be able to run close to
the cables to reduce the area of the loop between
cables and cable duct (fig. 25). The ways this can
be reached are discussed.
Connections of low impedance
The sidewalls of the cable ducts have a low
impedance due to their construction as broad
strips. The connections between the parts mutually
and between the cable duct and the cabinets
shall also be of low resistance and low
impedance. This connection can be achieved by
the use of lips or strips (splice plates) connected
with bolts. The lips or strips shall have heights
which are approximately the same as the height of
the cable duct (fig. 26, 27 and 28). The number of
bolts that must be used is discussed on page
H1E-1-19.
Low resistance between the parts of a cable duct
can be achieved by using bare metal surfaces
(galvanized or stainless steel) connected by bolts.
When the surfaces have a non-conducting finish
lockwashers have to be used to scratch through
the finish to make electrical contact (fig. 29).
lacquered
surface
lockwashers
Figure 29
Lockwashers are used to contact parts having
a non-conducting surface
The bonding resistance between two connected
parts shall be lower than 0,01W.
Figure 26 Cable ladders connected
by lips
Figure 27
Cable ladders connected
by splice plates
Figure 28
H1E-1-17
Cable ducts connected
by splice plates
Between the cable ducts and the cabinets to
which the cables are connected also broad plates
have to be installed (fig. 21, strip A).
A connection with wires between the parts is not
sufficient because of the high impedance of wires
at high frequencies.
In the connection between parts of the cable duct,
and also between cable ducts and cabinets, no
interruptions bridged with the help of wires may be
present. Some wrong constructions are shown,
accompanied by the right ones (fig. 30). Examples
are the interruption at wire branches (fig. 30a),
cable ducts going around a comer (fig. 30b) and
cable ducts carried through a wall (fig.30c).
(Fig. 30 is an improvement of the former fig. 26)
EMC
Application of the EMC-theory
to cable ducts
WRONG
wire
wall
GOOD
WRONG
wall
Figure. 30c
GOOD
Figure. 30a Cable duct with branch
Remark:
In connection with firesafety-instructions it is not
permitted in some cases to pass a metal cable duct
through a wall.
In that case it is advisable to fit the highest number of
permitted strand winding connections.
Figure. 30
WRONG
Cable duct fed through a wall
Connection between parts with wires
has a too high impedance
Shielding
Metal cable ducts provide shielding attenuation as
already mentioned at fig. 21. Of cable ladders only
the side panels provide shielding analogous to
fig. 21a. Open cable ducts have a high shielding
attenuation in the comers according to fig. 21c.
This is shown in fig. 31. These zones are especially
suited for the laying of susceptible cables.
Covered ducts give the highest shielding
attenuation.
GOOD
Figure 30b Cable duct at a corner
Figure. 31
Zones of a cable duct with the highest
shielding attenuation
H1E-1-18
EMC
Application of the EMC-theory
to cable ducts
Transfer impedance
Analog to the transfer impedance of wires, cable
ducts also have a transfer impedance.
The definition of the transfer impedance of cables
can be found in books on EMC (e.g. Ref 1 and 2).
The transfer impedance of a cable duct carrying a
cable is shown in fig. 32.
voltage
over cable
Ua
1m
cable duct
cable
I st
current source
U
transfer impedance Z t = a
I st
Figure 32
Transfer impedance of a cable duct
The transfer impedance Zt of a cable duct is
roughly the ratio between the voltage over the
cable Ua and the inducted current in the cable
duct (ICM):
The transfer impedance is specified per meter
length. The lower the transfer impedance of the
cable duct the lower the voltage which is coupled
into the cable. For a shielded cable this voltage is
induced over the cable shield.
The parts of the cable duct each have a low
impedance. In practice the impedance of the
cable duct is mainly determined by the impedance
of the connections between the parts and the
connections between the cable ducts and the
cabinets. By keeping these impedances low, a
current flowing in the cable duct will induce a low
voltage over the cable.
Experiments on a U-shaped cable duct have
shown (Ref. 4) that the increase of the number of
bolts used for a connection with strips from 4 to 12
decreases the transfer impedance at low frequencies (< 1 kHz) with a factor 2 and at higher
frequencies (> 10 kHz) with a factor 4.
An increase from 4 bolts to 8 bolts, which number
is often used in practice, decreases the transfer
impedance at low frequencies with a factor 1,5
and at higher frequencies with a factor 2 (fig. 33a).
The transition from a connection with two strips to
a connection with a U-shaped strip, fastened with
the same number of bolts, decreases the transfer
impedance at low frequencies with a factor 2 and
at higher frequencies with a factor 4 (fig. 33b).
Zt = Ua / ICM
a.
2 strips
4 bolts
2 strips
8 bolts
b.
2 strips
8 bolts
Figure 33 Connection methods between parts of a cable duct in
connection with the value of the transfer impedance
H1E-1-19
U-shaped inter coupler
8 bolts
Holes and perforations
For fastening purposes the cable ducts are
provided with holes. In practice these holes have
no noticeable influence on the transfer impedance.
Some types of cable ducts are provided with
perforation slots. The slots have to be punched in
the lengthway direction of the cable duct (fig. 34).
In that way currents in the cable duct will be
obstructed as little as possible. Slots lying
transverse to the lengthway shall not be used
(fig. 35).
EXCELLENT
POOR
GOOD
POOR
Figure 34
Slots in the lengthway
Figure 35
Slots transverse to the lengthway
H1E-1-20
EMC
Application of the EMC-theory
to cable ducts
EMC
Application of cable ducts
Cable laying on cable ducts
Cable ducts will be divided into some groups in
sequence of preference from an EMC point of
view:
- flat bottom cable ducts
- cable ladders
- wire mesh trays
In practice cable ladders are widely used.
When more than one cable category is laid on the
same cable duct a spacing between 15 cm (for flat
bottom cable ducts) and 20 cm (for cable ladders)
has to be applied between the categories (fig. 37).
Cables can be divided into three cable categories:
- indifferent cables, e.g. power cables
- sensitive cables, e.g. data cables
- jamming cables, e.g. control cables
The most sensitive and strongest jamming cables
have to be laid close to the beams or plates of the
cable ducts.
Preferably each cable category shall be placed in
a separate cable duct (fig. 36).
spacing
Figure 37 Spacing of 20 cm between cable categories
on a cable ladder
Cable categories have to be laid in sequence of
disturbing power of the signals. For instance the
indifferent group has to be laid as a shielding
barrier between the sensitive group and jamming
group (fig. 38).
spacing
Figure 38
earthing
system
Figure. 36
H1E-1-21
Separate cable duct for each cable category
Bounding of the cable ducts to the brackets
Indifferent cable category between
sensitive and jamming categories
Application of cable ladders and flat bottom cable
ducts
For 'normal' applications cable ladders are used.
These are applicable for cases where no strong
jamming or very sensitive EM-environment is
present.
Special situations may however be present such
as:
- strong jamming cables running through an EMenvironment with sensitive cables or
equipment
- very sensitive cables running through an EMenvironment with strong jamming cables or
equipment
- both strong jamming and very sensitive cables
are present.
In these cases often the use of cable ladders is
not sufficient to shield the cables. Use has to be
made of flat bottom ducts (fig. 39).
cover
EMC
Application of cable ducts
Figure 40 Connection with U-shaped inter coupler
When the foregoing-mentioned measures are
related to Table 2 then the signs in the table mean:
X - 'normal' cable laying, e.g. with cable ladders
E - extra. Extra measures needed, e.g. cable
ladders provided with perforated or solid
plates or the use of flat bottom ducts
EE - extra-extra. All available measures needed,
e.g. the use of flat bottom cable ducts with
Remark:
For most types of cable ladders covers are
available. Because the bottom side of the ducts
remains open the shielding attenuation of these
ducts with covers is limited. If necessary bottom
plates can be applied.
Figure 39 Flat bottom cable ducts have a shielding
effectivity. The shielding attenuation can be
enlarged by the use of covers.
Flat bottom cable ducts have the following
advantages with respect to cable ducts:
- more cables are situated on or close to a
conducting surface
- the shielding attenuation is larger than for cable
ladders.
The shielding attenuation can be improved by
installing covers over the ducts and by not filling
them with cables to the top, but to remain one or
more centimeters below the rim. The best way is to
use one or only a few layers.
By high demands on the shielding effectivity the
parts of the cable ducts shall not be connected by
strips but by U-shaped inter couplers (fig. 40).
These also reduce the transfer impedance of the
cable ducts.
Separation strips
In case more than one cable category is laid on a
cable duct, as well as applying distance between
the categories, separation strips may be used
between the categories (fig. 41). The cables may
be laid against both sides of the strips.
Figure 41
Cable duct with separation strips
H1E-1-22
EMC
Application of cable ducts
The separation strips shall be contacted with each
other. At branches the strips may be interrupted for
some length, but not for distances larger than 0,5
m (fig. 42). Separation strips function well, as the
cable categories on both sides differ no more than
one category. For open ducts there is a chance on
signal coupling when the cables differ more than
one category.
interruption in
separation strip
separation strip
Figure 42
Cable ladder with conducting plates and
separation strips
Cable ladders with additional plates
When in an EM-environment with strong jamming
or very sensitive signals cable ladders should be
used, these can be provided with bottom plates
(fig. 42). The plates have to be contacted with
each other. In this way the cable ladder resembles
a flat bottom duct. With high demands on the
shielding attenuation the cable ducts shall not be
fully filled with cables or covers shall be used.
Wire mesh trays
Wire mesh trays function as a PEC (Parallel Earth
Conductor) but have no shielding attenuation.
Wall channels
Wall channels are mainly used in office buildings.
When they have to fulfil EMC-requirements the
same measures as for cable ducts apply.
H1E-1-23
separation strip
Conclusion
EMC
From an EMC point of view cable ducts shall be of
metal. The parts of the ducts shall be connected
with a low impedance, both mutual and with the
cabinets, which also shall be constructed of metal.
The best way to achieve this is a connection with
broad plates of bare metals. In this way is
achieved an earthing plane under the cables and
an earthing system between the cabinets.
If next to that other EMC-measures as a good
earthing system and a separation of cables into
categories is present, the EMC of the installation
can be improved with simply means and the
chance on the occurrence of interference lowered.
Delden, October 2001
D.S.J.Schuuring M. Sc.
H1E-1-24
EMC
Annexes
Dimensions and conversion of units
H
= Wb/A
= V.s/A
Hz
= 1/s
W
= V/A
S
= 1/W
= A/V
T
= Wb/m2
Wb = V.s
= V/Hz
References
1. Henry W.Ott
Noise reduction techniques in electronic systems
John Wiley & sons, New York. Second edition
1988.
ISBN 0 471 85068 3
2. Bernard Keiser
Principles of electromagnetic compatibility
Artech House. 3rd edition 1987.
ISBN 0 89006 206 4
Abbreviations
CM Common-mode
DM
-
Differential Mode
3. IEC 61000-5-2
Electromagnetic Compatibility
Part 5: Installation and mitigation guidelines
Section 2: Earthing and cabling
EM EMC EMI EU
ElectroMagnetic
ElectroMagnetic Compatibility
ElectroMagnetic Interference
European Union
IEC
-
International Electrotechnical
Commission
PC
PE
PEC
PLC
-
Personal Computer
Protective earth
Parallel Earth Conductor
Programmable Logic Controller
Symbols and units of quantities
Symbol
Quantity
Unit
A
A
B
E
f
H
I
I
L
P
R
r
Z
area
attenuation
magnetic induction
electric field strength
frequency
magnetic field strength
current
length
self-inductance
power
resistance
distance
impedance
m
dB
T
V/m
Hz
A/m
A
m
H
W
W
m
W
d
skin depth
wavelength
specific resistivity
specific conductivity
magnetic flux
m
m
W.m
S/m
Wb
l
r
s
F
H1E-1-25
2
4. M.J.A.M van Helvoort
Grounding structures for the EMC-protection of
cabling and wiring
Thesis Technische Universiteit Eindhoven. 1995.
ISBN 90 386 0037 2
Introduction
Indications are made which cable ducts should be
used in the specific EM-environments of an
installation and which EMC-measures have to be
applied.
The following aspects will be treated:
- material
- measures
- connection of parts
- earthing and bonding
- cable categories
- shielding.
Material
The materials used for the cable ducts are:
- Mill galvanized steel
Thickness 1 - 2 mm
Zinc layer ca 22 µm
- Mill galvanized and lacquered steel
- Hot dip galvanized steel
Thickness 1,5 - 2 mm
Zinc layer 50 - 70 µm
- Stainless steel
Thickness 1 - 2 mm
- Aluminum, anodized.
Plastic as a material for cable ducts is not
discussed because this material is not conductive
and cannot be used to improve the EMC of the
installation.
The thickness of the material is not very important
from an EMC point of view. This is because at low
frequencies the resistance is dominant and
depends on the cross section of the conductor.
This is usually large enough because of
mechanical strength requirements. The thickness
is normally not smaller than 1 mm. The selfinductance has small values.
The thickness of the material at high frequencies
(above approximately 1 MHz) is for most metals
larger than the skin depth. In this situation the skin
layer determines the impedance.
Galvanized steel
From an EMC point of view the way the zinc is
applied on the steel makes no difference.
Galvanized steel has the following advantages:
- the connection places can be left bare without
a chance on corrosion
- the resistance between parts is low, which is
also the case for the self-inductance because of
the large contacting surface
Stainless steel
For the electrical contact between the parts the
same applies as for galvanized steel.
Aluminium
Aluminum as a construction material can be used
because of its low resistivity. A disadvantage is
that the surfaces can have an insulating oxyde
layer or can be anodised. The electrical contact
between parts has to be achieved via the bolts
with the help of lockwashers.
Lacquered surfaces
Lacquered surfaces insulate. To make electrical
contact the insulating layer has to be scratched
with the help of lockwashers, which intrude
through the layer.
From an EMC point of view the electrical contact
between parts provided with insulating layers is
less effective than between bare surfaces, since
the contact is only made via the bolts, while bare
materials make contact via a surface area.
Choice of material
In an EM-enviroment containing high frequency
signals both galvanized steel and stainless steel
can be used.
When low frequency signals, e.g. in the supply
frequency or harmonics, are also present, then
steel is prefered because of its high magnetic
permeablity, which achieves a higher shielding
attenuation at low frequencies.
Dimensions of cable ducts
The cross section of a cable duct is important for
the resistance of the cable duct, but the outline of
the cross section is important with respect to the
inductance. To keep the value of the inductance
low, the outline shall be large.
In this situation many cables can be laid directly
on the conducting surface. This improves the
decoupling of cables and the shielding attenuation
to the EM-environment.
In order of increasing size of cross section, the
cable ducts are:
- wire mesh trays
- cable ladders with small height
- cable ladders with large height
- flat bottom cable ducts with perforations
- flat bottom cable ducts with solid bottom
- cable ducts with covers.
H1E-1-26
EMC
Selection of cable duct types in
accordance with the EMC-requirements
EMC
Selection of cable duct types in
accordance with the EMC-requirements
Connection of the parts
The low impedance connection of the parts of the
cable ducts is important. This applies to the
connection between parts mutually and the
connection of the duct to cabinets.
In sequency of improving electrical contact holds:
- 2 strips on each side of the cable duct
- connection via lips (one transition instead of two)
- U-shaped inter coupler.
For all connections:
- increased number of connection bolts.
Earthing and bonding
The earthing and bonding of cable ducts is
achieved via the brackets and the connection to
cabinets. The bonding via brackets shall be at
distances not larger than 10 m.
Selection of cable ducts
The several types of Gouda Holland cable ducts
are discussed on the pages H1E-1-28 up untill
H1E-1-31. Requirements used in the selection of
cable ducts are:
- mechanical strength
- required width
- required heigth
- chemical requirements
- hygienic requirements
- cost considerations.
Cable ladders can be used in most situations. This
is the case, when the electrical and electronic
parts of the installation follow the EMCrequirements.
Cable ladder types are:
Unic
H60 and H100 : page H1E-1-28
Resist
H60 and H100 : page H1E-1-28
Crafty
H100 and H130 : page H1E-1-29
Streamline H40 and H60
: page H1E-1-29
When in the cable categories 'strong jamming' and
'very sensitive' only a few cables have to be laid,
flat bottom cable ducts can be applied on the
cable ladders to reduce coupling to other cables
and the EM-environment.
Flat bottom cable duct types are:
Tray
Lock
In an EM-environment where high disturbance
levels are present and cables of the cable
H1E-1-27
category 'sensitive' have to be laid, flat bottom
cable ducts are advised.
The same applies when 'jamming cables' are
present in an EM-environment with low levels.
Cable ducts with solid bottoms fulfil higher
requirements than cable ducts with perforated
bottoms.
If necessary these cable ducts can be provided
with covers.
Flat bottom cable duct types are:
Tray H28R and H53R (ZP or GP)
with (GP) or without (ZP) perforations
Lock OK3 and OK6: page H1E-1-31
In an EM-environment where very high disturbance
levels are present and cables of the cable
category 'very sensitive' have to be laid, flat bottom
cable ducts without perforations are advised. The
same applies when 'strong jamming cables' are
present in an EM-environment with low levels.
Cable ducts with solid bottoms fulfil higher
requirements than cable ducts with perforated
bottoms. If necessary these cable ducts can be
provided with covers.
Flat bottom cable duct types are:
Tray H28R and H53R: page H1E-1-30
without (ZP) perforations
Lock OK3 and OK6: page H1E-1-31
In an EM-environment where only disturbances of
low level are present or all disturbances are of the
same level wire mesh trays can be used. These
cable ducts function as PEC's (Parallel Earth
Conductors) and improve the EMC only slightly.
Wire Mesh Tray:
Tandem H53: page H1E-1-31
Plastic cable ducts do not improve the EMC of an
installation.
Selection of cable duct types in
accordance with the EMC-requirements
RESIST
Cable ladders
Cable ladders
EMC
UNIC
Material:
type H60
type H60
type H100
type H100
Mill galvanized steel
Mill galvanized and lacquered steel
Hot dip galvanized steel
Material:
Stainless steel AISI 304
Stainless steel AISI 316
Cable ladders can be used in most situations,
where the electrical and electronic devices of the
installation are fulfilling the EMC-requirements.
Cable ladders can be used in most situations,
where the electrical and electronic devices of the
installation are fulfilling the EMC-requirements.
Measures to increase the shielding effectivity to
reach EMC are the use of:
- flat bottoms cable ducts or bottom plates below
the cable categories 'very sensitive' and 'strong
jamming'
- use of covers.
With one or both of these extra measures the type
Unic also can be used in EM-environments with
high level disturbances.
Measures to increase the shielding effectivity to
reach EMC are the use of:
- flat bottoms cable ducts or bottom plates below
the cable categories 'very sensitive' and 'strong
jamming'
- use of covers.
With one or both of these extra measures the type
Resist also can be used in EM-environments with
high level disturbances.
H1E-1-28
Selection of cable duct types in
accordance with the EMC-requirements
STREAMLINE
Cable ladders
Cable ladders
EMC
CRAFTY
Material:
type H100
type H40
type H130
type H60
Hot dip galvanized steel
Stainless steel AISI 304
Stainless steel AISI 316
Material:
Stainless steel AISI 304
Stainless steel AISI 316
Cable ladders can be used in most situations,
where the electrical and electronic devices of the
installation are fulfilling the EMC-requirements.
Cable ladders can be used in most situations,
where the electrical and electronic devices of the
installation are fulfilling the EMC-requirements.
Measures to increase the shielding effectivity to
reach EMC are the use of:
- flat bottoms cable ducts or bottom plates below
the cable categories 'very sensitive' and 'strong
jamming'
- use of covers.
With one or both of these extra measures the type
Crafty also can be used in EM-environments with
high level disturbances.
Measures to increase the shielding effectivity to
reach EMC are the use of:
- flat bottoms cable ducts or bottom plates below
the cable categories 'very sensitive' and 'strong
jamming'
- use of covers.
With one or both of these extra measures the type
Streamline also can be used in EM-environments
with high level disturbances.
H1E-1-29
Selection of cable duct types in
accordance with the EMC-requirements
TRAY ZP
Flat bottom cable duct
perforated
Flat bottom cable duct
EMC
TRAY GP
Material:
type H28 and H28R
type H28R
type H53 and H53R
type H53R
Mill galvanized steel
Mill galvanized and lacquered steel
Hot dip galvanized steel
Stainless steel 304/316
Material:
Mill galvanized steel
Mill galvanized and lacquered steel
Hot dip galvanized steel
Perforated flat bottom cable ducts can be used in
most situations. They can be used for sensitive
cables in EM-environments with high level
disturbances and for strong jamming cables in
EM-environments containing low levels.
Flat bottom cable ducts can be used in most
situations. They can be used for sensitive cables in
EM-environments with high level disturbances and
for strong jamming cables in EM-environments
containing low levels.
Measures to increase the shielding effectivity are
the application of:
- covers
- U-shaped inter couplers.
Measures to increase the shielding effectivity are
the application of:
- covers
- U-shaped inter couplers.
H1E-1-30
Selection of cable duct types in
accordance with the EMC-requirements
TANDEM
Flat bottom cable duct
Wire mesh tray
EMC
LOCK
type OK3
type H30
type OK6
Material:
Stainless steel AISI 304
Stainless steel AISI 316
Flat bottom cable ducts can be used in most
situations. They can be used for sensitive cables in
EM-environments with high level disturbances and
for strong jamming cables in EM-environments
containing low levels.
Measures to increase the shielding effectivity are
the application of:
- covers
- U-shaped inter couplers.
H1E-1-31
Material:
Mill galvanized steel
Epoxy coating
Hot dip galvanized
Stainless steel AISI 304
Stainless steel AISI 316
In an EM-environment with only low level
disturbances or only disturbances with levels of
the same kind, wire mesh trays can be used.
These have no shielding attenuation, but improve
the EMC by their function as PEC (Parallel Earth
Conductor).
Index
aluminium
antenna behaviour
attenuation values
Biot and Savart, law of
bolts
bonding
bonding resistance
cable category
cable layout
cabinets
capacitive coupling
CM
common-mode
conducted disturbance
conduction
connection
connection methods
connection strips
coupling
coupling channel
CRAFTY
dB-values
decoupling
differential mode
disturbance
disturbing current
disturbing power
disturbing radiation
disturbing signal
disturbing voltage
DM
earth grid
earthing system
electric field
EMC
EMC-standards
EMI
emission
emittor
EM-environment
EM-zones
E-field
frequency domain
frequency ranges
galvanized steel
harmonics
holes
H-field
immunity
impedance
indifferent cables
inductive coupling
installation
H1E-1-27
H1E-1-10/15
H1E-1-17
H1E-1-9
H1E-1-21
H1E-1-29
H1E-1-20
H1E-1-14/23
H1E-1-13/23
H1E-1-18
H1E-1-6
H1E-1-7,19
H1E-1-7
H1E-1-5/6/7
H1E-1-6
H1E-1-28
H1E-1-21
H1E-1-19
H1E-1-6
H1E-1-6
H1E-1-29/31
H1E-1-17
H1E-1-15/26
H1E-1-7
H1E-1-5
H1E-1-7
H1E-1-7
H1E-1-5/6/7
H1E-1-5/7
H1E-1-7
H1E-1-7
H1E-1-17
H1E-1-17/29
H1E-1-7/10
H1E-1-5
H1E-1-6
H1E-1-5
H1E-1-5/6
H1E-1-5
H1E-1-5,14
H1E-1-14
H1E-1-7
H1E-1-7
H1E-1-6
H1E-1-28
H1E-1-6
H1E-1-22
H1E-1-7
H1E-1-6
H1E-1-6/8
H1E-1-14
H1E-1-6
H1E-1-5
Page
inter coupler
interference
inter-system EMC
intra-system EMC
jamming cables
Kirchhoff's law
Lenz's law
lips
LOCK
lockwashers
low frequency
magnetic flux
magnetic permeability
magnetic field
material
noisy cables
perforations
pulses
radar frequency range
radiation
RESIST
resistance
return current
self-inductance
sensitive cables
separation strips
shielding
shielding wall
skin depth
skin effect
slots
source
specific conductivity
specific resistivity
speed of light
splice plate
stainless steel
STREAMLINE
strong jamming cables
supply frequency
susceptibility
susceptor
TANDEM
three-element-model
time domain
transfer impedance
transition
transmission velocity
TRAY
UNIC
very sensitive cables
victim
wall channels
wavelength
H1E-1-24
H1E-1-5
H1E-1-5
H1E-1-5
H1E-1-14/24
H1E-1-11
H1E-1-11
H1E-1-19
H1E-1-29/33
H1E-1-20
H1E-1-6
H1E-1-10
H1E-1-10
H1E-1-7/9
H1E-1-28
H1E-1-14
H1E-1-22
H1E-1-7
H1E-1-6
H1E-1-6
H1E-1-29/30
H1E-1-8
H1E-1-11
H1E-1-8
H1E-1-14
H1E-1-24
H1E-1-16
H1E-1-17
H1E-1-11/12
H1E-1-8/11
H1E-1-22
H1E-1-5
H1E-1-12
H1E-1-12
H1E-1-10
H1E-1-18
H1E-1-28
H1E-1-29/31
H1E-1-14
H1E-1-6
H1E-1-5
H1E-1-5
H1E-1-29/33
H1E-1-6
H1E-1-7
H1E-1-21
H1E-1-21
H1E-1-10
H1E-1-29/32
H1E-1-29/30
H1E-1-14
H1E-1-5
H1E-1-25
H1E-1-10
H1E-1-32
EMC
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