Page
9
- Manual
FA01869-EN
- 08/2022 - © CAME S.p.A. - The contents of this manual may be changed, at any time, and without notice. - T
ranslation of the
original instructions
For long bus sections always install
the 150 ohm resistors between terminals A and B on both ends of
the bus.
Always set up the bus wiring in “input and output” mode. Do not
cable the bus in star configuration.
If this configuration is required follow the directions in this chapter.
CHOOSING THE CABLE SECTION FOR THE RS-485 BUS
For the RS-485 bus it is suggested to use the following cable:
• Twisted and grade 4-screened cable (600/1000 V).
• A twisted pair for data with cross-section 2x0.22 mm².
• A pair to power the 2x0.5 mm² or greater cross-section depending
on distances and voltages (check table below).
Below is the table for calculating the cross-section of power cables
with varying distances and power draws.
Any drops in power voltage must not exceed 1.4 V (voltage
measured on terminals of the power supply and those of the device
on the remotest bus).
MAXIMUM
CABLE LENGTH RS-
485
POWER ABSORPTION
0.1 A
0.25 A
0.5 A
1 A
CROSS-
SEC
TION
0.5 mm
2
175 m
70 m
35 m
17 m
0.75 mm
2
262 m
105 m
52 m
26 m
1 mm
2
350 m
140 m
70 m
35 m
1.5 mm
2
525 m
210 m
105 m
52 m
If a cable does not have the proper section additional auxiliary power
sources must be added.
Example:
If we have:
• PXC2-32
• PXKTB02 (maximum consumption 60 mA)
• PX4IOR (maximum consumption 40 mA)
• Sensors connected to the remote expansion inputs (total consump-
tion 150 mA)
• Connection distance 200 m.
With maximum consumption of 250 mA in this case we can either
use a 1.5 mm² section cable, or a 0.5 mm² section cable plus an aux-
iliary power supply connected at the end of the line as shown below:
APPLICATION NOTES ON BUS RS-485 CABLING
Cabling of the bus connecting the control unit to the plugs, bus am-
plifiers and keypads must follow the rules dictated by the RS-485.
Only use a screened and twisted cable with section of at least:
• 2x0.5 mm² for power supply and twisted 2x0.22mm² for data.
• 2x0.5 mm² for power supply and twisted 2x2x0.22 mm² for data
(used to perform branching).
The braid must always be continuous and connected to the control
unit’s negative (-) terminal.
The maximum length of the cable (max sections of 800m) and the
cross-section of the conductors depend on the number of modules
and the overall draw on the different bus sections. When power draw
increases the voltage drop on the cables increases and so reduces
the power supply current to the devices on bus.
The voltage at all + and - terminals of the devices on bus (keypads,
plugs, modules, ...) must not fall below 12 V DC.
If less, add an auxiliary power source and disconnect the positive
while keeping the negative mutual.
Greater than 12 Vdc
YES
NO