Siemens SIMATIC HMI KTP1200 Basic DP - 3.3.2 Connecting the equipotential bonding circuit

Mounting and connecting
3.3 Connecting the HMI device
Basic Panels 2nd Generation
28 Operating Instructions, 10/2016, A5E33293231-AB
3.3.2
Connecting the equipotential bonding circuit
Differences in electrical potential
Differences in electrical potential can develop between spatially separated system
components. Such electrical potential differences can lead to high equalizing currents on 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 conductors 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 conductor 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 shielding of the data cable from the HMI device flush at the equipotential rail
using suitable cable clamps. The equipotential rail should be very close to the HMI
device.
● Route the equipotential bonding conductor and data cables in parallel and with minimum
clearance between them.
Note
Equipotential bonding conductor
Cable shielding is not suitable for equipotential bonding. Always use the prescribed
equipotential bonding conductors. The cross
-section of the equipotential bonding conductor
must not be less than 16
mm². Always use cables with an adequate cross-section when
installing MPI and PROFIBUS DP networks. The interface modules may otherwise be
damaged or destroyed.