Siemens SIMATIC NET Betriebsanleitung PDF herunterladen (Seite 158)

Guidelines for Installing Networked Automation Systems in Buildings

7-10

SIMATIC NET Twisted-Pair and Fiber-Optic Networks

C79000-G8976-C125-02

Signal Connections in Existing Installations

If unexplained, sporadic disturbances occur in data processing systems or on their

communication connections, it is advisable to check for unwanted shield currents.

These can be measured simply by inserting the cable in question in a clip-on

ammeter. Currents higher than approximately 0.1 A indicate problems in the

electrical installation, for example in the TN-C system.

If the alternating current power system supplies a large number of electronic

devices or electronically controlled consumers the highest interference currents

can generally be observed at the third harmonic of the frequency.

Other signs of an unsuitable alternating current power supply are as follows:

S Currents on the PE conductor

S Currents through water pipes and heating pipes

S Progressive corrosion at grounding terminals, on lightning conductors, and

water pipes.

Remember that sporadic events such as switching, short circuits, or atmospheric

discharge (lightning strike) can cause current peaks in the system many times

higher than the average value.

Troubleshooting

The following measures are suitable for trouble shooting:

S Restructuring the power distribution system (to form a TN-S system)

S Replacing the electrical data cabling with fiber-optic cables

S Installing an equipotential bonding conductor parallel to the disturbed data

cabling.

Note

If shield currents on bus cables cause problems in communication, the safest

often cheapest solution is to replace the disturbed electrical bus connection with a

fiber-optic cable.

Help with structuring noise-free power supply systems

You will find the addresses of Siemens departments that will help you in the

planning and installation of noise-free power supply installations for

information-technology systems or in the detection and elimination of existing

installation errors in the appendix of this manual.

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Siemens SIMATIC NET Betriebsanleitung Seite 158