gonaads said:
One other thing to take into account is the strands of the wire itself. Stranded wire is by it's nature, compressable. It deforms to provide a high-reliabilty, high contact area connection. For vibration prone, and flexing applications. Technically speaking, stranded can carry more current than solid wire. Now you could have two top PSU manufacturers and one has 12 strands per wire. Then you have the other and their's has 20 strands per wire. Who's is going to be the better? Now throw this into the equation. The one with 12 strands is 16 AWG wire and the one with 20 strands is 14 AWG. Now which one conducts better?
Remember the small the wire the more resistance but if there are more strands then what?
Also current is moving electrons, they travel "through" the conductor and along the surface of the conductor. They move along the surface better because it is easier, so more current is distributed along the surface areas than in the center. Stranded conductors have a lot more surface area so they can carry more current for a given overall diameter. So, back to my question, The one with 12 strands is 16 AWG wire and the one with 20 strands is 14 AWG. Now which one conducts better? So If a modular PSU uses a more stranded wire setup that say a non modular PSU then would the resistance values still be the same?
More "surface", more current flow, and more heat dissipation (current flow creates heat) and less resistance and less voltage drop. Heat creates resistance.
I tried not to respond to this but..
Bull**** -
1) The characteristic you are talk around is called skin effect. It only applies at very high frequencies (radio frequencies) or very high current density (power transmission lines). At the power density in PC PSUs skin effect is negligible.
This link is almost in English but it is incomplete because it only talks about the frequency dependency of skin effect. At ultra high current densities even audio frequencies can exhibit skin effect. Note the table at the bottom of the link. At 1000Hz and less skin the depth is 0.2 CM which is much greater than the 18 AWG wire diameter so skin effect is non-existent.
http://home.san.rr.com/nessengr/techdata/skin/skindepth.html
Increasing the number of strands in a wire only improves skin effect if the individual strands are insulated from each other (the strands in PSU wires are not coated with varnish to insulate them). This is called Litz wire and is used in high frequency / high power applications. If the strands are not insulated they are all pressed together and form one big conductor with no skin effect improvement.
http://www.mwswire.com/litzmain.htm
3) Wire has a number stamped on it, in the case of a PC PSU it is 18AWG for the power wires, except for the -5V. That stands for American Wire Gauge. That number defines the electrical characteristic of the wire carrying DC/50Hz/60Hz, at the specified current density and it does not matter how many starnds are in the wire. If the resistance of the wire is lower they put a lower AWG number on it and charge more.
http://www.powerstream.com/Wire_Size.htm
Wire can be 18AWG with 6 strands (what we use at work) or 18AWG with 20 strands (in a PC cable I just pulled apart) but the current carrying capacity and resistance per foot is the same and defined by the AWG rating. Check some wire manufacturer web sites.
4) Using finely stranded wire is done for:
a)mechanical robustness (the finer strands undergo less mechanical compression and therefore less work hardening and embrittlement)
b) and improved bend radius (more strands makes wire more flexible which is why the PC PSU cables use such fine strands).
You would not be able to bend a cable bundle of 18AWG, 6 strand wires within the confined spaces of your PC to reach the connectors.
Finding a tech link about section 4) subject is left as an exercise for the student. (They were all on steel cable construction and I got bored looking so find your own on copper wire construction vs strength and flexibility.)
