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• Avoiding earth loops
Where a bus cable is routed between several buildings, ensure that earth loops are avoided. The
reason for this is that buildings actually have different potentials compared to the earth poten
-
tial. An earth loop is created when connecting one cable screen in each building
directly
with the
equipotential bonding system. In other words, a current flows from the higher to the lower poten
-
tial.
For example, if lightning strikes near one of the buildings, the potential of that building will briefly
be raised by several kV.
In this case, the equalizing current flows to earth via the bus screen and causes an extreme elec
-
tromagnetic input which can result in the destruction of the bus components.
Lightning protection
Efficient lighting protection is highly dependent on good building earthing that meets the relevant
regulations.
An external lightning protection system offers protection against a
direct
lightning strike.
In order to protect against voltage surges in the 230 V mains supply cable (
indirect
lightning strike),
appropriate lightning conductors and surge arresters compliant with local regulations must be fitted
in the upstream distribution systems.
In order to protect the individual components of a CAN network against
indirect
lightning strike, we
recommend the use of surge arresters specifically developed for bus systems.
Example:
CAN bus surge arresters CAN-UES from Technische Alternative
Gas discharge arrester for indirect earthing EPCOS N81-A90X
Examples of different network versions
Key to symbols:
„Small“ network (within one building):
Max. cable length: 1000 m at 50 kbit/s
The screen must be continued at each network node and be connected to the device earth (GND).
The screen earthing or GND must only be implemented
indirectly
via a gas discharge arrester.
Ensure that no unintentional
direct
connection of earth or screen and the earth potential is created
(e.g. via sensors and the earthed pipework).
… device with its own power supply (UVR16x2, UVR1611K, UVR1611S, UVR1611E)
… device is supplied by the bus (CAN I/O, CAN-MT, …)
… CAN-Repeater (CAN-RP)
… terminated (end devices)
… open termination
… CAN bus surge arrester
... gas discharge arrester for indirect earthing
