Siemens SIMATIC NET PROFIBUS, Owner'S Manual

Page: 276 / 490

Installing LAN Cables
C-14
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
Conditions
Grouping cables according to voltage classes assumes that the interference
voltages relate directly to the power supply voltage conducted (the lower the
supply voltage, the lower the interference voltage). Remember, however, that DC
or 50 Hz power supply voltages do not represent any danger to PROFIBUS
cables. The critical interference voltages in the kHz to MHz frequency range are
created by the “consumer” connected to the cable. A 24 V DC cable with which a
relay is switched regularly has a far more critical interference range than a 230 V
cable supplying a light bulb.
In the information shown below, it is assumed that all the components within an
automation system and all the plant components controlled by the system (for
example machines, robots etc.) at least meet the requirements of the European
standards for electromagnetic compatibility in an industrial environment. If devices
are defective or incorrectly installed, higher interference voltages must be
expected!
The following is assumed:
S
The cables for analog signals, data signals and process signals are always
shielded.
S
The distance from the cables to the chassis surface of the system (cabinet wall,
grounded cable channel, ...) is not more than 10 cm.
Note
In general, the greater the distance between cables and the shorter the distances
over which the cables run parallel to each other, the less the danger of
interference.
Clearance Table
Table C-1 contains the general rules for clearances between a variety of cables.
The rules should be understood as minimum rules for positioning LAN cables
within buildings (inside and outside cubicles).
How to Read the Table
To check how cables of different types must be laid, follow the steps outlined
below:
1. Find the cable type of the first cable in column 1 (cables for ...).
2. Find the cable type of the second cable in the relevant section in column 2 (and
cables for ...).
3. Read the guidelines for laying the cables in column 3 (lay ...).