Why do PSUs have multiple lines (cables) with the same voltage? (even if they are wired in parallel)

Question

For this question i need a technical\engineering answer.

Why are there multiple cables carrying the same voltage? Since they are wired in parallel both in the psu and in the motherboard (i checked with a volt-meter) it should suffice one cable per voltage (+ ground).

I get that some PSU have multiple rails on 12v for protecting against failures but for example the MotherBoard 20+4 pin connector is usually wired on a single rail and yet it has many wires with the same voltage.

I'm referring to ATX PSUs https://en.wikipedia.org/wiki/Power_supply_unit_(computer).

Thank you.

Answer 1

The multiple wires connecting to the same places at both ends, exist to carry a sufficient quantity of amperage with minimal voltage drop, through both the more metal carrying the electrons, and the critical connection points.

Many wires to the electrons is pretty much the same to them as one big fat wire, just like the water through the hose analogy. One big fat wire could end up a lot more rigid and difficult to deal with, stranded wiring, and multiple wires provides the Firemans hose of power through a bunch of flexable garden hoses , with simple connection methods.

Speaking of many smaller connections This is an example of how the very low voltage yet higher amperage connections on a CPU chip, the picture shows just how many of the pins on a cpu are there to provide the power.

Answer 2

A 600W PSU with an efficiency of 80% is able to supply a maximum current of about 40 Amp on the +12V output.

40 Amp on a single cable or on a single path on the mother board requires wider cable gauge than the actually used (18 wire gauge) because the actual cable probably will catch fire. Wider cables are less flexible, wider paths on the motherboard will make it larger and from then your system will be larger.

So the +12V is distributed through multiple paths and on the PSU is controlled so none of them carry more than 20 Amp.