CAUTION !!
RS485 BUS CONNECTION CABLES
The bus connections must be made from a twisted and shielded pair with equivalent characteristics to BELDEN
type 9841 or BELDEN 9842 cables indicated in the table below:
Power cable
Use flame-retardant cable of adequate section according to the devices connected to the control unit, the
section must never be less than 2.5 mmq.
Connection: Solenoid valves, Sirens, and other devices.
Calculate the cable section according to the length and the number of connected devices, in order to fall within
the power supply range of the devices which guarantees correct operation.
Connection: sensors, sirens, and other devices.
In order to avoid the use of conductors with high section, it is possible to power the devices point by point, by
means of individual switcing power supplies.
In the RS485 network, the masses of the devices must be connected together.
In the case of devices with power supply connected to earth (for example PC), the earth and ground connection
together can generate problems.
1) The total length of the RS485 network must not exceed 1000 meters.
2) The minimum distance between two devices must not be less than 1 meter.
3) The branch line from the main network must not exceed 2 meters.
4) The shield of the BUS cable must be connected to earth at one end, for example on the peripheral near the
control unit.
5) A second ground connection would not guarantee the equipotentiality of the screen.
Do not use the same conduit for Bus and power supply cables, or power cables in general...
follows .. Electrical Connections
RESISTENZE IN DC
NOMINAL CAPACITY
Type
N°
Wire
Shield
Nominal
Betwen wires Betwen wires AWG
Pair
Ohm/km
Ohm/km Impedence Ohm
pF/m
Shield
pF/m
BELDEN
9841
1
78,7
11,0
120
42,0
75,5
24
(0,25 mmq)
BELDEN
9842
2
78,7
7,2
120
42,0
75,5
24
(0,25 mmq)
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