3-3
Section
Sharing the Communications Power Supply
27
3-3
Sharing the Communications Power Supply
It is necessary to supply communications power to each node in the DeviceNet
network.
3-3-1 Prerequisite Conditions
•
The communications power supply must be 24 VDC.
•
The communications power supply must be connected to the trunk line.
•
When providing power to several nodes from one power supply, if possible try
to locate the nodes in both directions from the power supply.
•
Provide power through Power Supply Taps. It is, however, possible to use T-
branch Taps instead when there is one communications power supply in the
system and the total current consumption is less than 5 A.
•
The power supply capacity for cables is restricted to 8 A for thick cables and 3 A
for thin cables.
•
A single network is usually supplied by one power supply. It is, however, pos-
sible to have more than one power supply when power supply specifications
cannot be met with a single power supply. (See 3-3-6 Step 3: Splitting the Sys-
tem into Multiple Power Supplies.)
•
Fully consider the power supply capacity allowance in the design.
•
If the power supply is switched OFF during the operation of the network, there
may be a malfunction in the nodes.
•
The current capacity of the drop line varies according to its length. The longer
the drop line, the lower its maximum capacity becomes. This is the same
whether the cable is thick or thin. Calculate the current capacity passing
through the drop line I (the total current consumption at the drop line) using the
following formula.
I = 4.57/L
I: Permissible current (A)
L: Length of the drop line (m)
