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INSTALLATION AND OPERATING MANUAL
13.2 SYSTEM START-UP PROCEDURE
13.2.1 Technical verifications prior to start-up
Before starting up and powering the M-Bus system, it is important to check that the bus cable, M-bus devices and power
unit have been correctly installed.
Therefore, check:
• The electrical connections of the central unit and its power unit.
Remember that the data concentrator powers the bus networks with a 38-42 V DC output; before powering the sy-
stem, therefore, make sure the bus cable is “clean”, that is, that there is no voltage return.
E.g
.: M-bus system with meters powered at 220 V AC; the electrician connects the bus cable together with the power
cable by mistake; when the meters are powered, at 220 V AC, the bus cable has a voltage return of 220 V AC, which
enters the 38-42 V DC output of the convert which naturally burns out and has to be replaced.
N.B: the fitter must check that the electrical connections are correct. Any damage to the devices caused by
errors in electrical connections invalidate the product warranty.
• The bus cable used for centralising and data transmission.
The bus cable must observe the technical specifications in this manual and in other technical documents.
N.B: the manufacturer declines liability if, due to the use of an unsuitable bus cable, the central unit cannot
centralise or communicate with the M-Bus devices in the network.
• Bus connection.
Check that the bus network correctly reaches all the devices to centralise and that all the devices are correctly con-
nected to the bus cable.
N.B: the fitter must check that the bus cable is correctly fitted. The manufacturer declines liability for com-
munication problems between the central unit and the devices if the bus cable is fitted without observing the
technical specifications in this manual.
M-Bus search logic
Bus searching takes place according to the following logic:
1. Searching begins with the highest communication speed (Baud) and ends with the lowest. If a device responds to both
speeds, the central unit will take the highest speed as reference.
2. Searching begins with the secondary address and continues with the primary address. If searching is set for both
primary and secondary addresses, devices with both addresses will be searched for their secondary addresses, thus
omitting their primary ones. If they must be searched for their primary addresses, modify the search typology.
Bus cable resistance
Diameter [mm]
Section [mm
2
]
Resistance [Ω/km]
0.4
0.13
283
0.6
0.28
126
0.8
0.50
71
1.13
1.0
36
1.38
1.5
24
1.60
2.0
18
1.78
2.5
14
