User Manual

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Building Technologies M-bus System CE1P5361en
HVAC Products 5 Engineering 08.02.2007
Within a system, a maximum of 250 primary addresses can be assigned. Normally, the
primary addresses are assigned when setting up the M-bus devices. If there are more
than 250 devices in a system, secondary addressing must be used. Even the use of
repeaters cannot extend the space for primary addressing.
Secondary addressing is an address space extension of primary addressing. The sec-
ondary address comprises a total of 8 bytes. This offers an almost unlimited address
space. The assignment of manufacturers’ codes eliminates address conflicts between
products of different manufacture. Using unambiguous address assignment ex factory
and a special procedure, the devices can be identified without giving the M-bus devices
special addresses when setting up the system.
OZW10 and OZW111 can communicate with both primary-addressed and secondary-
addressed devices. The types of addressing can also be mixed. For more information,
refer to section 8.3 "Search run of central units OZW10 and OZW111".
5.4.3 Protection against transients
Especially in community and district heating systems, bus cables are also laid outside
the buildings. Hence, the devices are exposed to transients caused by lightning and
must therefore be protected.
 In general, protection against transients is required whenever the bus cables
leave the building
 Protective measures by Siemens are not required in the following situations:
The customer agrees that Siemens Building Technologies will have to assume no
responsibility should damage due to lightning occur
 All bus cables are laid inside the buildings
The proposed protection against transients does not offer protection against
 permanent overvoltages (mains voltage)
 transients that reach the M-bus devices via the house installation (water pipes,
mains connection)
Each bus cable and the devices that need to be protected call for specific protective
equipment. For this reason, only the tested components mentioned in section “8.2
Protection against transients “ may be used.
When laying the M-bus cable, the local regulations for electrical installations must be
complied with.
For detailed information about compliance with EMC directives, refer to Data Sheet
N2034.
5.4.4 Planning process
A number of factors have a considerable impact on planning M-bus plant:
 The number and types of M-bus devices used on the plant
 The distribution of the M-bus devices in the plant
 Mounting locations for the central unit, signal converters and repeaters
 The distances between the various M-bus devices
 The cable (type of cable, length and cross-sectional area)
 The data transmission rates
 The proposed planning stages of the M-bus plant
The major task of the planning process is to collect all information that is required and
to determine the number of locations for the central unit(s), signal converters and re-
Primary addressing
Secondary addressing
Introduction
Regulations
Restrictions
Components, mounting,
installation
Electrical installation