Mounting and connecting the HMI device
3.3 Connecting the device
Comfort Panels
Operating Instructions, 07/2017, A5E36770603-AB
47
Connecting the equipotential bonding circuit
Differences in electrical potential
Differences in electrical potential can develop between spatially separate system
components. Such electrical potential differences can lead to high equalizing currents across
the data cables and therefore to the destruction of their interfaces. Equalizing currents can
develop if the cable shielding is terminated at both ends and grounded to different system
parts.
Differences in potential may develop when a system is connected to different mains
supplies.
General requirements for equipotential bonding
Differences in potential must be reduced by means of equipotential bonding in order to
ensure trouble-free operation of the relevant components of the electronic system. The
following must therefore be observed when installing the equipotential bonding circuit:
● The effectiveness of equipotential bonding increases as the impedance of the
equipotential bonding conductor decreases or as its cross-section increases.
● If two system parts are interconnected by means of shielded data cables and their
shielding is bonded at both ends to the grounding/protective conductor, the impedance of
the additionally installed equipotential bonding cable must not exceed 10% of the
shielding impedance.
● The cross-section of an equipotential bonding conductor must be capable of handling the
maximum equalizing current. The best practical results for equipotential bonding between
two cabinets have been achieved with a minimum conductor cross-section of 16 mm².
● Use equipotential bonding conductors made of copper or galvanized steel. Establish a
large surface contact between the equipotential bonding conductors and the
grounding/protective conductor and protect them from corrosion.
● Clamp the shield of the data cable from the HMI device flush at the equipotential bonding
rail using suitable cable clamps. The equipotential bonding rail should be as close to the
HMI device as possible.
● Route the equipotential bonding conductor and data cables in parallel and with minimum
clearance in between.
Note
Equipotential bonding cable
Cable shields are not suitable for equipotential bonding. Always use the prescribed
equipotential bondi
ng conductors for this. An equipotential bonding conductor between
control cabinets must have a minimum cross
-section of 16 mm². The cable between the
ground bar and HMI device must have a minimum cross
-section of 4 mm
2
. Always use
cross-section when installing MPI and PROFIBUS DP networks.
Otherwise, the interface blocks may be damaged or destroyed.
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