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Building Technologies
Basic documentation: Communication via the KNX bus
CE1P3127en
HVAC Products
Appendix
30.08.2007
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.
230 V
230 V
Large loop area: Bad!
Small loop area: Good!
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Lightning can generate powerful surge voltages in loops, which cause short circuits
in devices and damage electronic components irreparably.
It is important right in the earliest project design phase to take care 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).
Avoiding loops
