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Guidelines for Installing Networked Automation Systems in Buildings

7-11

SIMATIC NET Twisted-Pair and Fiber-Optic Networks

C79000-G8976-C125-02

Example of Installing FOC in a TN-C-S System

Figure 7-1 illustrates the relationships between the structure of the alternating

current network, equipotential bonding system, and information technology cabling

in a building.

Three PCs and three S7-300 PLCs represent the information technology system.

These are networked using two OSMs. The casing of all the DTEs and the OSMs

are correctly connected to the grounding and bonding system of the building. The

PCs are connected to the system via the PE contact of their power supply cable.

The casing of the OSMs and the racks of the S7-300 PLCs are connected either

directly or via a switching cubicle casing locally to the CBN. The shields of the

twisted-pair cables interconnect all the device casings and are therefore connected

to the grounding and bonding systems at both ends.

The horizontal power distribution within a floor corresponds to the requirements of

a TN-S system. The neutral cable N and grounding conductor PE are separate

cables. The PE grounding conductor does not contribute to the power supply of the

devices. The parallel cable shields of the twisted-pair cables are therefore also free

of neutral cable currents.

The vertical, inter-floor parallel distribution is designed as a TN-C system (common

PEN cable for N and PE). The PEN is the return cable of the power supply of all

connected consumers. A connection between the two OSMs at the bottom

right-hand edge of the picture over shielded twisted-pair cables would allow the

return cable current of the PEN to flow through the entire bonding system, all PE

cables, and all cable shields on both floors. It is therefore strongly recommended to

implement the inter-floor connection between the two OSMs with fiber-optic cables.

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Siemens SIMATIC NET Instrucciones de operaciones Pagina 159