Basics
Infrastructure for EtherCAT/Ethernet
32
Version: 2.1
Fig. 29:
4-pair cable structure: unshielded UTP, overall shielded S (F)/UTP, overall shielded and shielded
pairs S (F)/STP
The following notes correspond to the state of the art. VDI guidelines, EN/IEC standards or EMC guidebooks
can be consulted as sources.
• The overall shield around the core pairs provides for protection against external electromagnetic
interference fields for the enclosed communication cores.
It is important for effectiveness that the shield coverage has a low impedance throughout and that it is
also implemented without interruption or holes at transition points (EN50174-2:2009, chapter 4.7).
Holes in the sense of this documentation are uncovered areas of the order of centimeters.
• The shield should be connected at each end of the cable to the machine earth via an electrically
conducting connection with a large surface area and low impedance. A pigtail, i.e. the twisting together
and point contact of the shield, must be avoided.
Fig. 30: Recommended shield connection
• If the shield is not earthed, there is no protection against the influence of magnetic fields.
• It must be ensured by means of sufficient parallel earthing in the plant that no equalizing current flows
via the shields of the communication cables. This can destroy connected devices.
Ethernet devices can therefore connect the shield to ground internally with an RC combination. Static
equalizing currents are this prevented, while high frequency interference is eliminated.
To support this, therefore, the shield of the communication cable should
additionally
be earthed with a
low impedance at the control cabinet entry point and, if necessary, on the device itself by suitable
means.
Beckhoff offers appropriate installation material in the ZB8500 product group.
