Wire Sizing for OCP: 5VDC/40A/200W PSU --> 5x 35W Load Devices

[pupdogg]

Looking to get expert opinions on what is the best way to accomplish this:

- We have a 120VAC switching PSU that outputs 5VDC/40A/200W. This unit has 3x Positive (+) and 3x Negative (-) terminals to hook up the load.
- I need to power 5x load devices that run on 5VDC and have a max power rating of 35W. This means that each device can technically use up to 7A. These load devices have small spade terminals where the largest compatible wire we can use with them is 16AWG.

Now, I understand that 16AWG (within reasonable distance...under 10ft) can be used for 10A at 90C with insignificant Voltage Drop for our use case. However, knowing that we only have 3 output terminals (on the PSU) to work with, could we output power using 3x sets of 14AWG cables and then branch off (using heat-shrink/UL-listed wire butts) to 2x sets of 16AWG cables each without any need for an inline fuse or an additional OCPD in-between this PSU's secondary (5VDC output) and our load devices?

I would really appreciate if someone can shine light on all different ways we can accomplish this task and still be compliant to OC protection on the supply conductors.

Notes:
- Changing to a different PSU is not an option anymore. In future, we will design the overall product using Class 2 PSUs where OCP does not come into play.

Any help would be greatly appreciated!!! Thank you in advance.

 

[gar]

171206-1127 EST

Copper wire at 20 C for #16 has a resistance of about 4 ohms per 1000 ft. You are indicating a loop length of 20 ft or 0.08 ohms. This would be a voltage drop of about 0.6 V. Can you tolerate this at 5 V?

Is the power supply current limiting (self protecting)?

Do you really care if your wires burn up? Is a dead short really very likely? Adding breakers will likely moderately increase voltage drop. V drop with a fuse might not be too bad.

My guess is that V drop is your big problem. That means bigger wire anyway. Three wire sizes is a resistance ratio of about 2 to 1. Changing from #16 to #10 would be a V drop of about 0.15 V.

A better approach is a local regulator at each load, and a source voltage of about 8 V. Now #16 is fine.

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