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Cable shields
•
Only use shielded data cables. The shield should be earthed at both ends. Make sure that no
parasitic currents can flow through the cable shields. This can be done by installing current-carrying
equipotential bondings.
•
A cable shield only earthed at one end can only protect from capacitively coupled interference and
low-frequency disturbances (50 Hz hum).
•
Use only cables with braided shields. Foil shields are not robust enough, cannot be contacted well
and have poor HF properties.
•
Only use metallic or metal-plated plugs for shielded data cables.
•
For analog signals, only use shielded cables. Earth the shield only at one end for small signals.
•
Earth the cable shield directly with a clip when entering the switch-gear cabinet. Do not cut the shield
until the cable reaches the module connected.
•
The connection between the PE bar and the shield bar must have a low impedance.
Switch-gear cabinet
•
The connections between the switch-gear cabinet, the mounting plates, the PE bar and the shield
bar must have a low impedance.
•
Earth the switch-gear cabinet doors with short and highly flexible conductors.
•
For illumination of the switch-gear cabinet, only use filament lamps (bulbs) or fluorescent tubes with
interference suppression to prevent the control system being disturbed.
•
For supplying the PC, use the mains socket which is located inside the switch-gear cabinet. In this
way, all earthing measures are performed with short conductors and no parasitic currents can flow
even in case of non-isolated interfaces.
Reference potential
•
Provide a uniform reference potential in the entire installation and earth all electrical appliances if
possible.
•
Route your earthing conductors in a star configuration so that no earth loops can occur.
____________________________________________________________________________________________________________
V2
AC500 Hardware
1-55
System data
AC500 / Issued: 05.2007
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