37
Network Configuration Section 2-2
2-2-3 Proper Cable Usage
The following table shows the limitations of the thin and thick cables.
Selecting between Thick
and Thin Cable
The branch line length and total branch line length limitations are the same for
both thin and thick cables. The cables differ in the following two capabilities.
1,2,3... 1. Maximum network length
With thin cable, the maximum network length is limited to 100 m in all cas-
es. At 500 kbps, the maximum network length is the same for both thick
and thin cables, so this limitation is not a consideration when the baud rate
is 500 kbps.
Thick and thin cable can be used in the same network, but the max. net-
work length declines as more thin cable is used. Refer to Combining Thick
and Thin Cables on page 37 for the equations used to calculate the max.
network length when thick and thin cable are used together.
2. Current capacity
In the trunk line, the cable current capacity (max. current allowed in the ca-
ble) is 3 A for thin cable and 8 A for thick cable. Consequently, thick cable
can provide a significantly higher current when the communications power
supply is being supplied through a Power Supply Tap. If thin cable is being
used, the current in any one direction is limited to 3 A regardless of the ca-
pacity of the 24 V DC power supply that is connected.
Note The communications power supply can also be supplied through a T-branch
Tap or T-branch Connector, but the current capacity of a T-branch Tap is 5 A.
The current capacity of the thin-cable T-branch Connectors is 3 A and the cur-
rent capacity of the thick-cable T-branch Connector is 8 A. Consequently, the
conditions for supplying power through a T-branch Tap or thin-cable T-branch
Connector are as follows: There can be only one communications power sup-
ply in the network and the total current consumption (in both directions) is lim-
ited to 5 A for a T-branch Tap or 3 A for a thin-cable T-branch Connector.
Combining Thick and Thin
Cables
Thick and thin cable can be combined in the line connecting most distant
nodes, but the max. network length will be shorter than it would be with thick
Cable type Baud rate Max. network
length
Branch
line length
Total branch
line length
Current
capacity
Thick cable 500 kbps 100 m 6 m max. 39 m 8 A
250 kbps 250 m 78 m
125 kbps 500 m 156 m
Thin cable 500 kbps 100 m 39 m 3 A
250 kbps 100 m 78 m
125 kbps 100 m 156 m
←→ ←→
←→
Power Supply Tap
Current
8 A max.
Current
8 A max.
Thick cable
Communications
power supply
Power Supply Tap
Current
8 A max.
Current
3 A max.
Thin cable
Communications
power supply
Thick cable
Power Supply Tap
Current
3 A max.
Current
3 A max.
Thin cable
Communications
power supply
Thin cable
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