Siemens SIMATIC NET PROFIBUS manual How do you avoid potential differences?

Installing LAN Cables

How do you avoid potential differences?

Potential differences must be reduced by installing bonding conductors so that the functions of the electronic components used are guaranteed.

When and why is equipotential bonding necessary?

The following reasons speak in favor of equipotential bonding:

SDevices with a grounded interface can be damaged by potential differences.

SThe shield of the PROFIBUS cable must not be used for equipotential bonding. This is, however, the case if parts of the system connected by the cable shield are connected to different grounding points.

SEquipotential bonding is a requirement for lightning protection.

Rules for Equipotential Bonding

Remember the following points about equipotential bonding systems:

SThe effectiveness of equipotential bonding is greater when the impedance of the bonding conductor is low.

SThe impedance of the additional bonding conductor must not exceed 10% of the shield impedance of the LAN cables.

SMake large-area contact between the bonding conductor and the PE conductor.

SProtect the bonding conductor from corrosion.

SInstall the bonding conductor so that the area enclosed by the bonding conductor and signal cables is as small as possible.

SUse copper or galvanized steel for the bonding conductor.

SInclude metal, conducting cable channels/racks in the equipotential bonding of the building and between the individual parts of the system. The individual segments of the channels/racks must be connected together with low inductance and low resistance and connected to the building ground system as often as possible. Expansion joints and angled connections should be bridged by additional flexible grounding bands.

The connections between the individual segments of channels must be protected from corrosion (long-term stability)

SIf there are connections between sections of buildings (for example separated

by expansion joints) with their own reference point for the building ground network, a bonding conductor (equivalent copper cross-sectional area ≥ 10mm2) must be installed parallel to the cables. This bonding conductor is not necessary if metal, conducting cable channels/racks are used.

PROFIBUS Networks SIMATIC NET	C-11
6GK1970-5CA20-0AA1 Release 2 05/2000