Requirements Of The Ac Power Distribution System - Siemens 6GK1 901-1GB01 System Manual

Installing network components in cabinets
3.3 Guidelines for setting up networked automation systems in buildings
For information about grounding and bonding techniques, refer to the system manuals of the
SIMATIC S7300 /9/, S7400 /10/ programmable controllers.
Note
Equipotential bonding is unnecessary if the sections of a system are connected exclusively
using fiberoptic cable (FO).
3.3.6.2

Requirements of the AC power distribution system

General
HD 384.3 S2 (IEC 603643:1993, modified, /22/) describes various power distribution
systems (TNS, TNC,S, TNC, TT and IT systems). Additional national or local regulations
stipulate the measures required for protection against electric shock and stipulate the
requirements for a grounding system (see also section 1.2 Protection against electric shock).
The outer surfaces of switching cubicles, device housings, connectors and bus cables are
conductive to provide shielding and must be connected to the grounding system to ensure
safety. To ensure that the EMC shield effect is achieved, they make further requirements of
the grounding system and grounding of the power distribution system. These result in an
alternating power distribution system with noncurrent carrying grounding conductors, for
example as in the TNS system.
Cable shields are part of the equipotential bonding network of a system.
Since the shields of twistedpair cables are included in the bonding system, all the currents
coupled into the bonding system of a building or plant flow through them.
Depending on the intensity and frequency range, these shield currents can cause
disturbances in data communication. Measures must therefore be taken to avoid the
alternating power distribution system of a plant including the bonding system in the power
return cabling. A TN-S system with separate cables or N and PE, for example, meets these
requirements. The EN 50310:2000 /21/ standard provides detailed guidelines for installing a
network system for supplying information technology equipment.
Note
End devices and /or network components connected over shielded twistedpair cables must
only be supplied by alternating power distribution systems whose grounding conductors
cannot contribute to the transmission of energy. There must be no PEN cable within the
entire system. This condition is met, for example, by a TNS system.
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Passive network components
System Manual, 02/2013, C79000-G8976-C282-01