Notes on Ethernet components – cables

For conformity, EN50173-1, chapter 7 requires the use of cables as per EN50288, twisted pairs. This includes both shielded and unshielded cables. Since shielded cables are recommended for EtherCAT cable connections, these will be dealt with exclusively below.

The relevant EN50288-2 standard contains sub-chapters on rigid and flexible cables. Twisted pairs or star quads are allowed as cable structures for both cables. The star quad is more advantageous: mechanically more stable (moving application, transverse compressive strength), lower space requirement, better NEXT values.

These standards contain, for example, the following data:

EN50288-2-1

Purpose: shielded cables -100 MHz, permanently installed for horizontal/vertical areas
‘Rigid wire structure’, solid copper conductors
Cross-section corresponds approx. to AWG24 to 21
Insertion loss max. 21.3 dB/100 m @ 100 MHz
DC loop resistance < 19 Ω / 100m

EN50288-2-2

Purpose: shielded cables -100 MHz, device connection cable
‘Flexible wire structure’, stranded wire – single or multi-strand conductors
must consist of 7 strands
Insertion loss max. 32 dB/100 m @ 100 MHz
DC loop resistance < 29 Ω / 100m

The data are valid for 20 °C.

Cables can be approved by the manufacturer according to the MICE classification as per EN50173-1, chapter 5 or appendix G for the ambient conditions specified therein.

	Patch cables & attenuation As can be seen from the technical data above, it is not possible to achieve an EN50173 Class D channel with its permissible insertion loss of 24 dB/100 m @ 100 MHz using a patch cable certified according to EN50288-2-2.The use of patch cables (according to EN50288-2-2) with a length of over 10 meters or the series connection of such cables is to be provided for only in acknowledgment of the technological restrictions.

For the combination of cable and plug connector, the class of the preconfigured patch cables/cords is defined together with permissible limit values in EN50173-1, chapter 9.

IEC61784-5-12 refers to this in its “Installation profile for EtherCAT networks” by specifying a max. connection length of 100 m using AWG22 cable (note: type EN50288-2-1).

	Screening An existing screen may increase the insertion loss of a cable among other things. This effect will only be noticeable in the case of great lengths. If the acceptance of a cable section fails for this reason, it is preferable, for example, to use larger core cross-sections rather than dispensing with shielded cables.A screen improves the return loss RL.

	"Similar to Cat.5" Since cable development has undergone technological progress since the creation of these standards, there are now numerous cables suitable for Ethernet communication on the market which • have the required electrical characteristics as per EN50173ff as a specification, but which • do not meet or exceed individual (mechanical) specifications according to EN50288. Such cables are identified, for example, by the remark “Similar to Cat.5” in the data sheet and can be used according to the manufacturer’s specifications – this is then a case of application-specific cabling, which should be subjected to a certification test after the installation if necessary.

Cable structure

Diameters dimensioned according to AWG (American Wire Gage) are specified as AWGxx/y: xx = AWG number, y = number of cores

Example:

AWG22/1 means single core, diameter AWG22.
AWG22/7 means 7 cores, overall cross-section corresponds to AWG22.

The cable structure according to ISO/IEC11801 is specified as follows:

Notes on Ethernet components – cables 4: — Cable structure

	Cable structure The exclusive use of completely shielded transmission links is recommended, e.g. SF/FTP, S/FTP or SF/UTP.Ensure the correct connection of the screen in the end devices. Observe the notes on this.