EMC implementation - Communication networks: Difference between revisions

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


*Characteristic impedance
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.
*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).
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.
 
[[Image:Fig_R17_2013.jpg|none|700px]]
'''''Fig. R17 :''''' ''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.
 
[[Image:Fig_R18_2013.jpg|none|700px]]
'''''Fig. R18 :''''' ''TVS reduces the arcing voltage''
 
To minimize these High Frequency disturbances the following solutions could be implemented. '''(In grey, the preferred choice).'''
 
{| style="width: 770px; height: 201px" cellspacing="1" cellpadding="1" width="770" border="1"
|-
| bgcolor="#0099cc" | '''Symbol'''
| bgcolor="#0099cc" | '''Transient Voltage <br> Suppression type '''
| bgcolor="#0099cc" | '''For AC
| bgcolor="#0099cc" | '''For DC'''
| bgcolor="#0099cc" | '''Overvoltage limitation'''
| bgcolor="#0099cc" | '''Contact fall time'''
|-
| bgcolor="#9FA0A4" | [[Image:Fig_R19a.jpg|none]]
| bgcolor="#9FA0A4" | R-C network
| bgcolor="#9FA0A4" | Y
| bgcolor="#9FA0A4" | Y
| bgcolor="#9FA0A4" | 2 to 3 . Un
| bgcolor="#9FA0A4" | 1 to 2 times the standard time
|-
| bgcolor="#9FA0A4" | [[Image:Fig_R19b.jpg|none]]
| bgcolor="#9FA0A4" | Metal Oxide Varistor
| bgcolor="#9FA0A4" | Y
| bgcolor="#9FA0A4" | Y
| bgcolor="#9FA0A4" | < 3 . Un
| bgcolor="#9FA0A4" | 1.1 to 1.5 times the standard time
|-
| bgcolor="#9FA0A4" | [[Image:Fig_R19c.jpg|none]]
| bgcolor="#9FA0A4" | Transient Voltage Suppression Diode Bidirectional
| bgcolor="#9FA0A4" | Y
| bgcolor="#9FA0A4" | Y
| bgcolor="#9FA0A4" | < 2. Un
| bgcolor="#9FA0A4" | 1.1 to 1.5 times the standard time
|-
| [[Image:Fig_R19d.jpg|none]]
| Transient Voltage Suppression Diode Directional
| N
| Y
| Un + 0.7 V
| 3 to 10 times the standard time
|-
| [[Image:Fig_R19e.jpg|none]]
| Free wheeling diode
| N
| Y
| Un + 0.7 V
| 3 to 10 times the standard time
|-
| [[Image:Fig_R19f.jpg|none]]
| Resistor
| Y
| Y
| < 4 . Un
| 1.5 to 2.5 times the standard time
|}
'''''Fig. R19:''''' ''TVS table information''
 
To be efficient, the TVS shall be installed closely to the coil.


[[ru:Конструктивное исполнение ЭМС - сети связи]]
[[ru:Конструктивное исполнение ЭМС - сети связи]]
[[zh:电磁兼容实施 - 通信网络]]
[[zh:电磁兼容实施 - 通信网络]]

Revision as of 13:50, 19 October 2013

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 R17 2013.jpg

Fig. R17 : 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 R18 2013.jpg

Fig. R18 : TVS reduces the arcing voltage

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

Symbol Transient Voltage
Suppression type 		For AC For DC Overvoltage limitation Contact fall time
Fig R19a.jpg
 R-C network Y Y 2 to 3 . Un 1 to 2 times the standard time
Fig R19b.jpg
 Metal Oxide Varistor Y Y < 3 . Un 1.1 to 1.5 times the standard time
Fig R19c.jpg
 Transient Voltage Suppression Diode Bidirectional Y Y < 2. Un 1.1 to 1.5 times the standard time
Fig R19d.jpg
 Transient Voltage Suppression Diode Directional N Y Un + 0.7 V 3 to 10 times the standard time
Fig R19e.jpg
 Free wheeling diode N Y Un + 0.7 V 3 to 10 times the standard time
Fig R19f.jpg
 Resistor Y Y < 4 . Un 1.5 to 2.5 times the standard time

Fig. R19: TVS table information

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

ru:Конструктивное исполнение ЭМС - сети связи zh:电磁兼容实施 - 通信网络

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