Hitachi S10mini LQS070 Hardware Manual page 62

6 CABLING
Furthermore, the maximum current capacity of a drop line becomes smaller as the drop line
becomes longer, which is true to both thick and thin cables. The maximum current
capacity I (a total amount of currents consumed in the branch) of a branch can be calculated
by equation below.
I = 4.75/L (less than 8 A for the thick cable or less than 3 A for the thin cable)
Given,
I: Current capacity of a branch (A)
L: Branch length (m)
If the maximum current capacity of branch is less than the total amount of currents
consumed by nodes connected to the branch, take the following measures:
• Shorten the branch.
• If the drop line has a plurality of nodes, branch some of the nodes to the other drop
line.
After making sure the total amount of currents consumed by nodes is less than the maximum
current capacity of branch, determines the disposition of the power supply considering
decrease in a voltage running in the main line. There are two ways of determined a power
supply disposition.
• simple calculation using a graph
• formula that figure out the voltage drop from a resistance and a consumed current of a
communication cable
If the method the former method is satisfactory, the power supply can be placed at the
assumed disposition. The former method assumes the worst disposition in terms of power
supply. Even when the requirements are not met, the expression may show as valid. In
this case the power supply can be located on the calculated point.
(1) Simple calculation using a graph
Disposition of the power supply can be determined by fast and easy method by using
this method. Note that the graphs to be referred are different according to the type of
the main line cables (thick cable or thin cable).
Refer to the table in the next page to find the maximum current capacity of the cables
against lengths of all the main lines.
If total current consumption of all nodes does not exceed the maximum current
capacity the power supply can be placed anywhere.
If the total current consumption of all nodes exceeds the maximum current capacity, try
the list below. If any of these measures does not work, reduce the amount of voltage
using formula in section (2) in which the actual disposition of the nodes are considered.
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