Operating instructions

Guidelines for Installing Networked Automation Systems in Buildings
7-7
SIMATIC NET Twisted-Pair and Fiber-Optic Networks
C79000-G8976-C125-02
7.3.2 Equipotential Bonding System
Aims of Bonding
The noise immunity of extended electronic automation systems or, in general,
information technology systems largely depends on the suitable design of the
grounding and bonding system of the building.
Equipotential bonding and grounding have two essential aims:
S Protection from the dangers of electricity
– by limiting the contact voltage and creating a fault to ground path
S Improvement of electromagnetic compatibility
– by creating a reference potential and equalizing potential differences
between parts of the system
– by shielding
Causes of Potential Differences
Wherever electric currents flow, magnetic fields are produced that in turn induce
stray currents in electrically conductive materials. Induced stray currents can
therefore not be avoided in the vicinity of electrical consumers (drives, electronic
controls, lighting etc.) and their power supply cables. They spread in all conductor
loops. Conductor loops are formed by parts of buildings such as metal bannisters
on staircases, water pipes or central heating pipes as well as through the shields of
electrical data cables and the protective ground connectors of electrical devices
(PE). The flow of current produces a voltage drop. This can be measured as a
potential difference between two locations within the system.
Extremely high potential differences between two grounding points result from
lightning strikes.
Effects of Potential Differences in Information Technology Systems
If locations with different grounding potential are connected via cables, currents will
flow. The currents flow on all connections between these two points, for example
also on the signal cables or cable shields connecting them. Attached devices can
be disturbed or even destroyed.
The aim of a grounding and bonding system is to ensure that the currents flow in
the grounding system and not in the electronic circuits.