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Ⓑ
Ⓐ
ENGLISH
Page
5
- Manual code:
FA00464-EN
ver
.
1
03/2017 © C
AME S.p.a. - The data and information shown in this manual ar
e t
o be consider
ed as subject t
o change at any time and without the need for any advance warning.
Greater than 12V DC
YES
NO
Always do the bus cabling in "entry-exit" mode Do not cable the
bus in a star configuration
If this configuration is required follow the instructions given in this
section
Where there are long bus sections always install 150 ohm resistors
between terminals A and B at both ends of the bus
The maximum length of the cable (maximum sections of 800 m)
and the cross-section of the conductors depend on the number of
modules and the overall power draw on the different bus sections
As the power consumed increases the voltage drop on the cables
increases and therefore the power supplied to the devices on the
bus is reduced
The voltage at all the + and – terminals of the devices on the bus
(keypads, readers, modules, etc ) must not be less than 12V DC
If less, add an auxiliary power unit, disconnecting the positive and
keeping the negative in common
Cabling RS-485 bus
PRACTICAL NOTES ON CABLING OF RS-485 BUS
Cabling of the bus connecting the control unit to the readers, key-
pads and amplifiers must follow the rules dictated by the RS-485
Only use shielded and twisted pair cable with a cross-section of
at least:
Ⓐ
2 x 0 5 mm² for power supply and twisted pair 2 x 0 22
mm² for data
Ⓑ
2 x 0 5 mm² for power supply and twisted pair 2 x 2 x
0 22 mm² for data (used to implement branching)
The sheathing must be continuous and connected to the control
unit’s negative (-) terminal
CHOICE OF BUS RS-485 CABLE CROSS-SECTION
The recommended cable for the RS-485 bus is:
• Twisted cable shielded to level 4 (600/1000 V)
• A twisted pair for section data 2 x 0 22 mm²
• A pair for the power cable 2 x 0 5 mm² or greater in
cross-section depending on distances and voltages
(check table below)
Below is the table for calculating the cross-section of power cables
for different distances and power draws
RS-485 CABLE
MAXIMUM LENGTH
POWER DRAW
0 1 A
0 25 A
0 5 A
1 A
CROSS-
SECTION
0 5 mm2
175 m
70 m
35 m
17 m
0 75 mm2
262 m
105 m
52 m
26 m
1 mm2
350 m
140 m
70 m
35 m
1 5 mm2
525 m
210 m
105 m
52 m
Any drops in power voltage must not exceed 1 4 V (voltage
measured on power supply terminals and those of the device on
the remotest bus)
Where no cable of suitable cross-section is available, additional
auxiliary power supplies must be used
Example: Let's suppose we have a connection at a distance of 200
m:
∙
A PXWKTB01/PXWKTN01 keypad (maximum power draw
60mA)
∙
A PXITU transponder reader (maximum power draw
100mA)
∙
A PXWRX radio expansion module (maximum power draw
100mA)
With a maximum power draw of 260 mA in this case use either a
cable with cross-section 1 5 mm², or use a 0 5 mm² cable and an
auxiliary power supply connected at the end of the line, as shown
below:
