II - DCE FEL ČVUT v Praze

1.6 Equipotential Bonding in Systems with Explosion Protection
Equipotential
bonding in a
building
Mechanical Configuration of an Automation System with SIMATIC S7 Ex Modules
I/O Modules with Intrinsically-Safe Signals
C79000-G7076-C152-04
Differences in potential can develop between the elements of electrical
apparatus, connected with PE conductors, and conductive structural
elements, piping etc. which does not pertain to the electrical apparatus. When
implementing measures to bridge these differences in potential, sparks
capable of causing ignition can be produced. To equalize the potentials,
conductive metal parts which are accessible and can be touched must be
connected to each other and to the PE conductor. Equipotential bonding with
the PE conductor can be best implemented at the distribution board. The
cross section of the bonding conductor must be at least that of the PE
conductor. In all other cases, the equipotential bonding conductor must have
a cross section of at least 10 mm2 of copper.
The Ex modules feature metallic isolation between the backplane bus and the
I/O circuit; there is therefore no need for connection to the equipotential
bonding conductor. An exception is when a connection to the EB conductor
must be made for measurement purposes. Where lightning protection devices
are required in the intrinsically safe circuit (Section 1.9), they must be
connected to the EB conductor at the same point as the shield of the
intrinsically safe circuits.
Generally, the measures described in DIN VDE 0165 (Table 1-1) should be
implemented or complied with.
Cable racks must be incorporated throughout the earthing system.
In accordance with VDE 0100, Part 410 and Part 540 and DIN VDE 0185,
equipotential bonding must be provided in every building and via the overall
cabling of the automation system; if this is not the case, it must be installed.
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