Siemens S7-400 Installation Manual page 260

Assembling and Installing Systems
Rule 4: Special EMC Measures
Employ special EMC measures for particular applications (see Section 4.11).
• Fit suppressors to all inductors which are not controlled by S7-400 modules.
• Use incandescent bulbs or suppressed fluorescent lamps in the immediate
vicinity of your controller for illuminating cabinets or housings.
Rule 5: Standard Reference Potential
Create a standard reference potential; ground all electrical apparatus if possible
(see Sections 4.10 and 4.12).
• Install equipotential bonding conductors of sufficient rating when potential
differences exist or are expected between sections of your system.
• Use specific grounding measures. Grounding the control system is a protective
and functional measure.
• Connect the system sections and cabinets containing central racks and
expansion racks to the grounding/protective ground system in a star
configuration. This prevents the formation of ground loops.
See also
Cable shielding, page A-13
Cabling outside buildings, page A-19
Cabling inside buildings, page A-17
Mounting of programmable controllers for EMC, page A-9
A-8
S7-400 and M7-400 Programmable Controllers Hardware and Installation
A5E00069481-04