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- Installation Manual
24805490/11-01-2013 319F90C
ver
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The data and information in this manual may be changed at any time with no obligation on BRAHMS’
s par
t t
o notify anyone of this
ENGLISH
APPLICATIVE NOTES ON CABLING OF THE RS-485 BUS
Cabling of the bus connecting the control unit to the remote modules, inserters, 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 2x0.22 mm² twisted for data.
• 2x0.5 mm² for power supply and 2x2x0.22 mm² twisted for data
(used to perform branching).
The sock must always be continuous and connected to the control unit’s
negative (-) terminal.
The maximum length of the cable (max stretches of 800 m) and the conductor
sections depend on the number of modules and from the overall draw on
the different stretches of bus. When power draw increases the voltage drop
increases on the cables and so reduces the power supply current to the
devices on bus.
The voltage at all + and - terminals of the devices on bus (keypads, inserters,
modules, ...) must not fall below 12 V DC.
If less, add an auxiliary power source and disconnect the positive while
keeping the negative mutual.
In case of long stretches of bus always install 150 ohm resistors among
terminals A and B at both ends of the bus.
Always carry out cabling of the bus in “enter and output” mode. Do not cable
the bus when in star configuration.
If you need this configuration follow the directions in this chapter.
Greater than 12 Vdc
NO
CHOOSING THE CABLE SECTION FOR THE RS-485 BUS
For the RS-485 bus we suggest using the following cable:
• Twisted and grade 4-screened cable (600/1000 V).
• A twisted pair for data with section 2x0.22 mm².
• One pair to power the 2x0.5 mm2 or greater section depending on distances and voltages (check table below).
Below is the table for calculating the section of power cables with distance variances and power draws.
Any drops in power voltage must not exceed 1.4 V (voltage measured on terminals of the power source and those of the
devices with remotest bus).
MAXIMUM CABLE LENGTH BUS RS-485
POWER DRAW
SEC
TION
0,1 A
0,25 A
0,5 A
1 A
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.
YES
