Cable length and cross-sections -35 – Rockwell Automation 1760-xxxx Pico GFX-70 Controllers User Manual User Manual
Page 69

Publication 1760-UM002B-EN-P - March 2005
Installation 2-35
Cable Length and Cross-Sections
For correct operation of the network, the cable lengths, cross-sections and
cable resistances must correspond to the following table.
The surge impedance of the cables used must be 120
Ω
.
Calculating the Cable Length with Known Cable Resistance
If the resistance of the cable per unit of length is known (resistance per unit
length R’ in
Ω
/m), the entire cable resistance R
L
must not exceed the following
values. R
L
depends on the selected baud rates:
l
max
= maximum cable length in m
R
L
= Total cable resistance in
Ω
R’ = Cable resistance per unit length in
Ω
/m
Table 2.43
Cable length
Cable Resistance
Cross-section
m
m
Ω/m
mm
2
AWG
up to 40
≤ 140
0.13
26
up to 175
≤ 70
0.25 to 0.34
23, 22
up to 250
≤ 60
0.34 to 0.5
22, 21, 20
up to 400
≤ 40
0.5 to 0.6
20, 19
up to 600
≤ 26
0.75 to 0.8
18
up to 1000
≤ 16
1.5
16
Baud rate
Cable resistance R
L
kBaud
Ω
10 to 125
≤ 30
250
≤ 25
500
1000
≤ 12
l
max
= R
L
R’
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