4 Equipotential Bonding
Equipotential bonding must not be confused with protection against electric shock
by means of a protective line system. This protective measure must be performed
according to the appropriate standards and guidelines and is not a constituent
part of these EMC Guidelines.
Why is equipotential bonding necessary?
Control components between which a signal connection exists also require a
potential connection. System malfunctions of the electrical components are
prevented by equipotential bonding between the electrical components among
each other and the earth.
Where is equipotential bonding required?
a) Between all control components which are also interconnected to each other
b) Between control components and the central earthing bar.
The central earthing bar is a bus bar for all earth, equipotential bonding and
protective conductors of a control cabinet. The external protective conductor or
the building earthing system is also connected to this bus.
A potential connection is not necessary for control components with potential-free
signal transmission (e. g. via light wave conductor), in many cases it is also not
No direct potential connection line is required (applicable to all digital signal
transmissions between the central appliance and the cabinet external components)
for control components, for which the signal transmission is conditionally potential-
free, i.e. it is only potential-free up to a certain voltage level. Here a short potential
connection to the respective earth (reference potential) is sufficient.
© Siemens AG, 2004. All rights reserved
EMC Installation Guideline – Planning Guide (EMV) – 03.2004 Edition