Siemens SIMATIC NET PROFIBUS - Manual (Page 265)

Installing LAN Cables
C-3
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
C.2 Electrical Safety
The signal levels on electric PROFIBUS cables are low voltage. Correctly installed
and operated PROFIBUS LAN cables do not have dangerous electrical voltages.
Remember, however, the following rules when installing the power supply for all
components (nodes, bus components, etc.) that you want to connect to a
PROFIBUS cable.
Power Supply Voltage
Between components operated on mains power supply and the PROFIBUS
interface, the requirements of safe electrical isolation from the power supply
complying with DIN VDE 0160 and DIN IEC 950/VDE 0805/EN 60950/ UL 1950/
CSA 22.2 No. 950 must be met. /7/
24 V DC Power Supply
24 V DC power supplies for components must meet the requirements of low
voltage with safe electrical isolation from the network complying with DIN VDE
0160 and DIN IEC 950/ VDE 0805/EN 60950/ UL 1950/ CSA 22.2 No. 950 must be
met. /7/
Protection from External Electrical Influences
Cable or wire breaks must not lead to undefined statuses in the plant or system.