Overvoltages In Loops - Siemens RXB Series Basic Documentation

Avoid loops
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Siemens
Building Technologies
9.7.3

Overvoltages in loops

Loops are frequently the cause of electromagnetic interference (EMI) and surges
resulting from lightning strikes. Loops occur when two independent networks (e.g.
the KNX network and the AC 230 V mains network) are connected to one bus
device.
Lightning can generate powerful surge voltages in loops, which cause short circuits
in devices and damage electronic components irreparably.
It is important at the outset of engineering to avoid loops where possible, or to keep
the extent of any loops (the "loop area") as small as possible. The formation of
loops must be considered in relation to the entire installation and all conductive
components must be taken into account, because the significant aspect of a loop is
its overall area.
Note also:
Bus and mains voltage conductors (power cables) must be routed as close
together as possible. This also applies to earthed components, if they are in
contact with the bus devices during normal operation.
The distance between conductor ends, earthed components and other
conductor ends should be as great as possible.
Maintain an adequate distance from the lighting protection system (e.g. from
arresters).
KNX bus communications
Appendix
Large loop area: Bad!
Small loop area: Good!
230 V
230 V
For internal use only
CE1P3127en
2013-04-08