Cable Current Rating

http://uk.rs-online.com/web/p/switchgear-tri-rated-cable/8034092/
http://uk.rs-online.com/web/p/hookup-equipment-wire/0361591/

I am trying hard to understand why these 2 extremely similar 0.5mm² CSA copper wires, have such a huge difference in current rating, 11A and 3A. The main factor I am seeing is the "Insulation Wall Thickness", which is a 0.2mm difference. Does 0.2mm actually warrants an almost 4x difference in current rating? The different AWG adds more to the confusion, as I don't understand why are they different if they both have a CSA of 0.5mm². Hope someone could point me to the right direction.

Seems confused. You need to select attributes. One is tinned copper and the other not. Tinned copper always carries higher current.

The rating for internal wiring (cable runs inside trunking) is much lower than for use as hookup wire
inside equipment where the wires are not confined and thus can be convention-cooled by the air.

You'll see a similar split in ratings for mains extension cables for fully unwound v. not fully unwound.

kesirajus:
One is tinned copper and the other not.

They are both copper.

lg, couka

The insulation thickness doesn't affect current carrying capability. (The type of insulation might make a difference because of different melting temperatures, but in most applications you want to keep the current low enough that the wire doesn't get hot.)

The insulation is related to voltage rating, and these ratings are determined by regulatory agencies.

The AWG should define the total cross-sectional area so I don't know why there's a difference.

There is a chart on [u]this page[/u] shows different ratings for chassis wiring and power transmission.

Different regulatory agencies may have different requirements, and in some applications voltage drop is the biggest consideration. i.e. For house wiring, longer runs may require heavier wire to keep the voltage drop within reason.

You can probably exceed the "rated" current carrying capacity if heat doesn't cause a problem in your application and if your circuit can handle the voltage drop. In "real life" it's usually terminals & connectors that "burn-up" (wires rarely burn-up in the middle) and it's a good idea to de-rate wires & connectors rather than pushing them to their limits.

The insulation on tri-rated is flame retardant and designed for higher operating temperatures. See here for further information.

There are numerous grades and quality of copper and I suspect the lower rated copper cables aren't the same as the higher rated ones.

Thanks for all your inputs.