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EMC Compatible enclosure assembly

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The Rittal EMC conceptThe definition of electromagnetic

compatibility (EMC) is

the 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

against interference.

With the enclosure, as a housing

for electrical/electronic

controls and systems, the following

points must be observed:

● These days, the intelligence

contained inside

enclosures is becoming

ever faster, i. e. shorter

switching times and

steeper pulse edges,

leading to ever higher

frequencies of voltages

and currents.

● Ever lower energy consumption,

● Technical progress will

exacerbate these risks

even 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,

the use of an RF shielded

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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 between

components and

cables, causing ever more

frequent interference on

different paths.

the use of an RF shielded

enclosure with a

superior 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 conducting

measurements.

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.

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

Comprehensive potential equalization connections

L < About 2”

A ≥ 0.015 in2

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In practice:

Maximum possible cross section, large-area

conductive mounting, low-inductive (therefore,

a rectangle is better than a round conductor).


2

3

1 Plain washer and

spring lock washer

Screw connection

Spring lock washer

7


8


1 Green with yellow stripe conductor

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How to connect metallic cable

tray to the enclosure

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1 Conductive connection

Contact paint provides protection against corrosion2


Conductive connection of

metallic cable tray

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Conductive connection of

metallic cable ducts

L < About 2”

A ≥ 0.015 in2

12


13

Conductive attachment of

metallic cable trays


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Conductive connection between machine and system components

L < About 2”

A ≥ 0.015 in2

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

Measures within the enclosure

2

1 High outputs

Low outputs

More powerful

Components

Mains

Dividing area

Actuators

3

4

5

6

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Actuators

Transducers,

probes,

Detectors

Shielded

enclosures

6

7

8

Protect sensitive assemblies by means of

encapsulation, shielded case / sub rack within

the enclosure

Measures within the enclosure for optimum shielding effect

2

1 Shielded viewing window, as small as

possible

Conductive seal between the enclosure

and removable enclosure panels

Enclosure within an enclosure

Potential equalization via suitable rails

or conductive mounting plate

Air-conditioning apertures with RF filters

3

4

5

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Air-conditioning apertures with RF filters

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

Optimum potential equalization of enclosure surfaces

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L < About 2”

A ≥ 0.015 in2

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 a

conductive housing can be

conductively mounted

with a large contact area.

Shielding interface with the enclosure

Ideal to have all-round EMC

cable glands

Conductive metal sheet

1

5

EMC gland plates


2

5

EMC shield bus


3

5

Potential equalization on the

mounting plate


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

Filters

Important:

Spatially separate

input and output

cables from one

another; use as

shielded cables

22

2

1

3

4

5


Control assembly

Output: To actuator or machine

Filter

Power supply

Filters

2

1 Conductive metal sheet

Control assembly

23

3

4

5

Output: To actuator or machine

Filter

Power supply

Filters

1

2

3


Filter

Power supply

Important:

Ensure there is large-area conductive

connection between the filter housing and

the mounting surface;

avoid cable loops to the reference potential.

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avoid cable loops to the reference potential.

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

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

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

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 clamps

or other fastening components

PVC plastic conduit,

surface mounted

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

Cables emission and interference sensitivity in cable trays

Unshielded cable

Large as possibleD

Unshielded cable

Immunity to Interference

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Shielded cable

Very sensitive

Sensitive

Immunity to

Interference

Interference

Emission

High

Low

Potential equalization of shielded cable

Reference potential

(machine chassis

or separate rail)

1

l= Lambda: Wavelength of the maximum

frequency 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

Cable routing

Connect unused conductor

to reference potential

32

Keep cables perpendicular wherever possible, and ensure adequate distance

between interference-emitting and sensitive cables.

1

2

3

Output

Control

Signals

Information from Rittal: Practical assembly tips

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emc compatible enclosure assembly - · pdf filetechnical progress will ... tray for power...

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