EMC implementation - Communication networks: Difference between revisions

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It is highly recommended to follow the European Standards EN 50173 series to perform Information Technology cablings.


Communication networks cover large distances and interconnect equipment installed in rooms that may have distribution systems with different system earthing arrangements. In addition, if the various sites are not equipotential, high transient currents and major differences in potential may occur between the various devices connected to the networks. As noted above, this is the case when insulation faults and lightning strikes occur. The dielectric withstand capacity (between live conductors and exposed conductive parts) of communication cards installed in PCs or PLCs generally does not exceed 500 V. At best, the withstand capacity can reach 1.5 kV. In meshed installations with the TN-S system and relatively small communication networks, this level of withstand capacity is acceptable. In all cases, however, protection against lightning strikes (common and differential modes) is recommended.<br>The type of communication cable employed is an important parameter. It must be suited to the type of transmission. To create a reliable communication link, the following parameters must be taken into account:
To ensure a reliable data transmission, the quality of the whole link shall be homogeneous. That means the category of the different cables shall be the same, the connecting interfaces shall be adapted to the cables.


*Characteristic impedance
Cables and connections of different categories may be mixed within a channel however the resultant performance will be determined by the category of the lowest performing component.
*Twisted pairs or other arrangement
*Resistance and capacitance per unit length
*Signal attenutation per unit length
*The type(s) of shielding used


In addition, it is important to use symmetrical (differential) transmission links because they offer higher performance in terms of EMC.<br>In environments with severe EM conditions, however, or for wide communication networks between installations that are not or are only slightly equipotential, in conjunction with IT, TT or TN-C systems, it is highly recommended to use optical fibre links.<br>For safety reasons, the optical fibre must not have metal parts (risk of electric shock if the fibre links two areas with different potentials).
The shield continuity of the whole link (patch cords, Terminal Outlets, horizontal cable) shall be ensured and controlled by tests.
 
The Terminal Outlets (TO) could be used to earth the screen terminations in the cabinet. The choice of these TO is very important.
 
Communication networks are mostly extensive. They interconnect equipment located in different areas where the feeding power supplies could have different earthing systems.
 
{{FigImage|DB422781_EN|svg|R19|How to reduce disturbing currents loop}}
 
If these different areas are not well equipotential, harsh transient currents could appear (lightning, main power fault, etc.) causing high voltage potential differences between interconnected equipment.
 
Communication interfaces (board, module, etc.) could be disturbed or damaged by this common mode over voltages.
 
The use of TN-S earthing system and well equipotential installation minimize this issue.
 
In any case, the use of Surge Protective Device (SPD) installed in Common Mode and/or Differential Mode is recommended.
 
If the different areas/zones are not equipotential, if the power supply earthing system is TN-C or IT, or if there is a doubt and the previous 2 points, optical fiber links are highly recommended.
 
To avoid electrical safety issue, the optical fiber link should not have any metallic parts.
 
== Protection against coils disturbances ==
 
AC and mostly DC Coils (relay, contactor, actuator, etc.) are very disturbing sources.
 
{{FigImage|DB422782|svg|R20|TVS reduces the arcing voltage}}
 
To minimize these High Frequency disturbances the following solutions could be implemented. '''(In grey, the preferred choice).'''
 
{{tb-start|id=Tab1441|num=R21|title=TVS table information|cols=4}}
{| class="wikitable"
|-
! Symbol
! Transient Voltage
Suppression type
! For AC
! For DC
! Overvoltage limitation
! Contact fall time
|-
| {{tb-HC2}} style="text-align:center;" | [[File:DB422783.png]]
| {{tb-HC2}} | R-C network
| {{tb-HC2}} | Y
| {{tb-HC2}} | Y
| {{tb-HC2}} | 2 to 3 . Un
| {{tb-HC2}} | 1 to 2 times the standard time
|-
| {{tb-HC2}} style="text-align:center;" | [[File:DB422784.png]]
| {{tb-HC2}} | Metal Oxide Varistor
| {{tb-HC2}} | Y
| {{tb-HC2}} | Y
| {{tb-HC2}} | < 3 . Un
| {{tb-HC2}} | 1.1 to 1.5 times the standard time
|-
| {{tb-HC2}} style="text-align:center;" | [[File:DB422785.png]]
| {{tb-HC2}} | Transient Voltage
Suppression Diode <br>
Bidirectional
| {{tb-HC2}} | Y
| {{tb-HC2}} | Y
| {{tb-HC2}} | < 2. Un
| {{tb-HC2}} | 1.1 to 1.5 times the standard time
|-
| style="text-align:center;" | [[File:DB422786.png]]
| Transient Voltage
Suppression Diode <br>
Directional
| N
| Y
| Un + 0.7 V
| 3 to 10 times the standard time
|-
| style="text-align:center;" | [[File:DB422787.png]]
| Free wheeling diode
| N
| Y
| Un + 0.7 V
| 3 to 10 times the standard time
|-
| style="text-align:center;" | [[File:DB422788.png]]
| Resistor
| Y
| Y
| < 4 . Un
| 1.5 to 2.5 times the standard time
|}
 
To be efficient, the TVS shall be installed closely to the coil.

Latest revision as of 09:48, 22 June 2022

It is highly recommended to follow the European Standards EN 50173 series to perform Information Technology cablings.

To ensure a reliable data transmission, the quality of the whole link shall be homogeneous. That means the category of the different cables shall be the same, the connecting interfaces shall be adapted to the cables.

Cables and connections of different categories may be mixed within a channel however the resultant performance will be determined by the category of the lowest performing component.

The shield continuity of the whole link (patch cords, Terminal Outlets, horizontal cable) shall be ensured and controlled by tests.

The Terminal Outlets (TO) could be used to earth the screen terminations in the cabinet. The choice of these TO is very important.

Communication networks are mostly extensive. They interconnect equipment located in different areas where the feeding power supplies could have different earthing systems.

Fig. R19 – How to reduce disturbing currents loop

If these different areas are not well equipotential, harsh transient currents could appear (lightning, main power fault, etc.) causing high voltage potential differences between interconnected equipment.

Communication interfaces (board, module, etc.) could be disturbed or damaged by this common mode over voltages.

The use of TN-S earthing system and well equipotential installation minimize this issue.

In any case, the use of Surge Protective Device (SPD) installed in Common Mode and/or Differential Mode is recommended.

If the different areas/zones are not equipotential, if the power supply earthing system is TN-C or IT, or if there is a doubt and the previous 2 points, optical fiber links are highly recommended.

To avoid electrical safety issue, the optical fiber link should not have any metallic parts.

Protection against coils disturbances

AC and mostly DC Coils (relay, contactor, actuator, etc.) are very disturbing sources.

Fig. R20 – TVS reduces the arcing voltage

To minimize these High Frequency disturbances the following solutions could be implemented. (In grey, the preferred choice).

Fig. R21 – TVS table information
Symbol Transient Voltage

Suppression type

For AC For DC Overvoltage limitation Contact fall time
DB422783.png R-C network Y Y 2 to 3 . Un 1 to 2 times the standard time
DB422784.png Metal Oxide Varistor Y Y < 3 . Un 1.1 to 1.5 times the standard time
DB422785.png Transient Voltage

Suppression Diode
Bidirectional

Y Y < 2. Un 1.1 to 1.5 times the standard time
DB422786.png Transient Voltage

Suppression Diode
Directional

N Y Un + 0.7 V 3 to 10 times the standard time
DB422787.png Free wheeling diode N Y Un + 0.7 V 3 to 10 times the standard time
DB422788.png Resistor Y Y < 4 . Un 1.5 to 2.5 times the standard time

To be efficient, the TVS shall be installed closely to the coil.

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