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EMC Compatible enclosure assembly
1
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The Rittal EMC conceptThe definition of electromagnetic
compatibility (EMC) isthe ability of an electrical
device to function satisfactorily
in its electromagnetic environment
without adversely
affecting this environment,
which may include other
equipment.
On the basis of this, the
essential requirements of
EMC are: To prevent/reduce
interference emission and
to offer defined resistance
With the enclosure, as a housing
for electrical/electroniccontrols and systems, the following
points must be observed:
These days, the intelligence
contained inside
enclosures is becoming
ever faster, i. e. shorterswitching times and
steeper pulse edges,
leading to ever higher
frequencies of voltages
and currents.
Technical progress will
exacerbate these riskseven further.
A standard enclosure made of
coated sheet steel can make
a significant contribution
towards the EMC of controls
for machinery and systems,provided some simple population
rules are taken into
account.
In applications with high frequency
field-bound interference,
2
against interference.
EMC is an indispensable element
of quality, and the protection
requirements regulated
by law, along with the
technical risks must be taken
into account at the planning
stage when developing equipment.
Ever lower energy consumption,
i. e. lower voltage/current levels, means
that components are more
readily influenced by interference.
The sitting of controls in
ever more confined spaces,
i. e. smaller distances betweencomponents and
cables, causing ever more
frequent interference on
different paths.
the use of an RF shielded
enclosure with asuperior shielding effect may
be required. The only way to
draw definite conclusions
about the type of enclosure
which is necessary or adequate
to comply with certain
standard limits is by conductingmeasurements.
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Explanation of symbols
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Comprehensive potential equalization grounding grid
1 Enclosure for power distribution
Enclosure for control and measurement
technology
Tray for power cable
Tray for low-power cable
2
3
4
4
Steel reinforcement in
concrete ceilings, metallic
bases in false ceilings
5
Earth connections
For EMC purposes, ideally there should be low and high-frequency
potential equalization between all metallic masses, enclosures,
machine and system components, which should be meshed as
closely as possible.
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Comprehensive potential equalization routing
A Power supply
Data/control connection
Enclosure
Cable
Earth connection
Reference potential
B
2
3
4
1
5
Loop
Enclosure
Machine
Measuring device
Cable routing in machinery and equipment
Basic principle: Avoid large cable loops; lay current-carrying cables as close as possible to
the reference potential.
5
6
7
8
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Comprehensive potential equalization connections
L < About 2
A 0.015 in2
6
In practice:Maximum possible cross section, large-area
conductive mounting, low-inductive (therefore,
a rectangle is better than a round conductor).
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Comprehensive potential equalization connections
2
3
1 Plain washer and
spring lock washer
Screw connection
Spring lock washer
7
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Comprehensive potential equalization connections
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Comprehensive potential equalization connections
1 Green with yellow stripe conductor
9
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Comprehensive potential equalization connections
How to connect metallic cable
tray to the enclosure
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1 Conductive connection
Contact paint provides protection against corrosion2
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Comprehensive potential equalization connections
Conductive connection of
metallic cable tray
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Comprehensive potential equalization connections
Conductive connection of
metallic cable ducts
L < About 2
A 0.015 in2
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Comprehensive potential equalization connections
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Conductive attachment of
metallic cable trays
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Comprehensive potential equalization connections
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Conductive connection between machine and system components
L < About 2
A 0.015 in2
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2
1 High outputs
Low outputs
Functional enclosure layout / spatial division
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Functional enclosure layout / spatial division
2
1 High outputs
Low outputs
Inputs3
16
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Measures within the enclosure
2
1 High outputs
Low outputs
More powerful
Components
Mains
Dividing area
3
4
5
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Transducers,
probes,
Detectors
Shielded
enclosures
7
8
Protect sensitive assemblies by means of
encapsulation, shielded case / sub rack within
the enclosure
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Measures within the enclosure for optimum shielding effect
2
1 Shielded viewing window, as small aspossible
Conductive seal between the enclosure
and removable enclosure panels
Enclosure within an enclosure
Potential equalization via suitable rails
or conductive mounting plate
3
4
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r-con t on ng apertures w t ters
Actuators
Mains filter/overvoltage protection at the
point of entry, with large-area contact
Unshielded control cables via filter
openings conductively connected
to the enclosure entry point
Shielded cables via EMC cable glands
5
6
7
8
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Optimum potential equalization of enclosure surfaces
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L < About 2
A 0.015 in2
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Enclosure back panel as a potential equalization surface
2
3
1 Conductive mounting
plate
Long PE conductor
Painted sheet metal
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L < About 2
A 0.015 in2
All components with aconductive housing can be
conductively mounted
with a large contact area.
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Shielding interface with the enclosure
Ideal to have all-round EMC
cable glands
Conductive metal sheet
1
5
EMC gland plates
Conductive metal sheet
2
5
EMC shield bus
Conductive metal sheet
3
5
Potential equalization on the
mounting plate
Conductive metal sheet
4
5
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Cable shields should be contacted directly at the point of cable entry, where possible.
Solder ring terminal Tin plated braiding Soldered earth strap
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Filters
Important:Spatially separate
input and output
cables from one
another; use as
shielded cables
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2
1
3
4
5
Conductive metal sheet
Control assembly
Output: To actuator or machine
Filter
Power supply
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Filters
2
1 Conductive metal sheet
Control assembly
23
3
4
5
Output: To actuator or machine
Filter
Power supply
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Filters
1
2
3
Conductive metal sheet
Filter
Power supply
Important:
Ensure there is large-area conductive
connection between the filter housing and
the mounting surface;
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.
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Transformers
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1 Conductive metal sheet
Position transformers on gland plates with large-area conduction,
conductive connection of the shield
2 Plastic material or painted
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Cabling rules, cable selection, and routing
Immunity to
interference
of connected
equipment
Shielded, twisted cable pair Shielded, twisted cable pair with
extra shielding
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Unused conductor
Multi-conductor wire Unshielded, twisted cable pair
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Cabling rules, cable selection, and routing
Immunity to
interference
of connected
equipment
Unshielded multi-conductor cable Shielded multi-conductor cable
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Shielded multi-conductor
cable, in metal conduit
or in metallic cable tray
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Cabling routing between panels and machine/system parts
Steel conduit Steel cable tray Steel cable tray or
Sheet steel supports
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Sheathings,open laying of bus cables etc. Surface cabling with cable clampsor other fastening components PVC plastic conduit,surface mounted
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Cabling routing in tray selection / population
Closed metallic cable tray Plastic cable tray
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Open metal cable tray Open metal mounting angle
Areas with effective shielding
against electromagnetic fields
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Cables emission and interference sensitivity in cable trays
Unshielded cable
Large as possibleD
Unshielded cable
Immunit to Interference
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Shielded cable
Very sensitive
Sensitive
Interference Emission
High
Low
l l f h ld d bl
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Potential equalization of shielded cable
Reference potential(machine chassis
or separate rail)
1
l= Lambda: Wavelength of the maximumfrequency occurring in the vicinity
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Reference potential
or potential
equalization rail with
connection to the
chassis
2
Cable shield with
potential equalization on one side
Cable shield without
potential equalization contact
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Cable routing
Connect unused conductor
to reference potential
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Keep cables perpendicular wherever possible, and ensure adequate distance
between interference-emitting and sensitive cables.
1
2
3
Output
Control
Signals
f f l l bl
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Information from Rittal: Practical assembly tips
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