Siemens SIMATIC NET PROFIBUS - Manual (Page 161)

Passive Components for RS-485 Networks
4-63
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
4.8 Cable Connections
4.8.1 Cable Connections to Network Components
Sometimes, a connection between two different LAN cable sections is necessary,
for example, a transition from the standard LAN cable to a section with trailing
cable.
The easiest way to implement this transition is to use the two LAN cable
attachments of a bus connector, bus terminal or repeater. The attachment of the
cables is described in detail in this chapter. For information about laying cables and
mechanical protection of the cables refer to Appendix C “Installing LAN Cables”.
For the transition from the underground cable to the standard LAN cable, it is
advisable to protect against overvoltage (see Appendix B “Lightning and
Overvoltage Protection”.
4.8.2 Cable Connection without Bus Connection Elements
Sometimes, a connection is necessary between LAN cable sections at locations
where no nodes or network component connections are intended, for example,
when repairing a broken LAN cable. Note the following information:
The all-round shielding of the LAN cable must be retained
To make the cable connection, use, for example, a commercially available sub-D
male connector and socket with metal casing. Only sub-D components with a
spring shield collar ensure a reliable shield connection.
Avoid accidental shield contact with the environment.
The male connector shield should not make any undefined, accidental contact to
conductive parts, since this can lead to undefined shield currents. Connect the
connector casing either permanently to ground potential or wrap the connector in
insulation that reliably prevents contact.