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Basic Concepts Section 3-1
3-1 Basic Concepts
• The communications power supply must be 24 V DC.
• Always supply the power from the trunk line.
• When providing power to several nodes from one power supply, try to
locate the power supply near the center of the nodes.
• Provide power through Power Supply Taps. It is possible to use a T-
branch Tap or T-branch Connector instead of a Power Supply Tap when
there is one communications power supply in the system and the current
consumption is within the specifications of the T-branch Tap or T-branch
Connector. Refer to 2-3-4 T-branch Taps or 2-3-5 Shielded T-branch Con-
nectors for details on the current limitations of these components.
• The power supply capacity for cables is restricted to 8 A for Thick Cables,
3 A for Thin Cables, and 5 A for Flat Cables.
• Environment-resistive Slaves are wired with Thin Cable, so the current
through a cable to an Environment-resistive Slave is limited to 3 A.
• A single network is usually supplied by one power supply, however, it is
possible to have more than one power supply when power supply require-
ments cannot be met with a single power supply. (See 3-6 Step 3: Split-
ting the System into Multiple Power Supplies.)
• Provide some extra power supply capacity in the network to allow for
future expansion and extend the life of the power supply.
• Turning OFF the communications power supply during operation can
cause errors in the other nodes if the other power supplies are left ON.
• The current capacity of a branch line ranges from 0.75 to 3 A, depending
on its length. Use the following equation to calculate the current capacity.
(The maximum current capacity of a branch line is 3 A, even if the branch
line is shorter than 1.53 m.)
I = 4.57/L I: Permissible current (A)
L: Length of the branch line (m)
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