In the following diagram, each square represents a device(PCB) and the devices are daisy-chained by a 3C cable and everything is in DC. The 24V comes from a power supply. The 3C cable current rating will be the largest among the 3 lines.

Current in each line:

Line A: 120W/24V = 5A

Line B: 12W/5V = 2.4A

Line C: The ground is being shared by 24V and 5V, what current rating cable should this line be using?

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  • \$\begingroup\$ How long is the cable? What voltage drop can you tolerate? \$\endgroup\$
    – Kartman
    Sep 20, 2021 at 3:04

1 Answer 1


There is one segment among the 30 devices where the ground wire must carry \$\frac{9}{10}\$ × 5 A + 2.4 A, for a total of 6.9 A. In all of the other segments, the ground current is less.


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