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Power Capabilities of a DeviceNet Cable System
A DeviceNet cable system has several power rating constraints. The cable type and the length
of the cable specify the maximum current on a cable. Thick and thin cable have:
24 VDC power rating
l
Optional power-supply tabs
l
If the power supplies are equipped with Schottky diodes, the optional power supply tabs must
be protected from bus back-feeding of current among the power supplies on the bus. We also
recommended the use of fuse protection for every trunk line in the cable system.
The maximum current rating of a thick cable trunk line is 8 A. Verify that this complies with
your national and international standards. It might be necessary to limit the maximum current
to a lower value if standards in the U.S. or Canada apply. The maximum current value is a
theoretical value. The cable size supports a higher current than 8 A. Depending on the topol-
ogy of nodes relative to the power supply, higher currents might be possible. See the DeviceNet
technical specifications for further information.
The maximum current rating of a thin cable trunk line is 3 A. If you use the thin cable on a
long line, the resistance of the cable decreases the maximum current value. See the following
table and the DeviceNet technical specifications for further information.
Table 7-5. Maximum Current on a Drop Line Relative to its Length
Length of Drop Line
1.5 m (5 ft)
2.0 m (6.6 ft)
3.3 m (10 ft)
4.5 m (15 ft)
6 m (20 ft)
For the calculation of the maximum current at a specific length, use the following formula:
Where:
l= Length of the drop line in meters (m)
i= Maximum current in amps
This calculation applies to the sum of the currents of all the nodes on the selected drop line.
The length (l) is not the cumulative length of the drop line; it is the maximum distance from
any node on the drop line to the trunk line.
Adept SmartController EX User's Guide, Rev.C
Chapter 7: Adept DeviceNet
Maximum Current
3 A
2 A
1
1.5 A
1 A
0.75 A
Page 92 of 96
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