Cable Rating?

Please read up about the skin effect (click here).

you are talking about derating factor because if current is more then inductance of line will increase as well as the effect of capacitance,thats why larger cable size taking less than your expectation as compared to low flow(A) current cable.

Just I will give you one important things that if cable size less than or equal to 16 sq.mm

then Z=R,i mean capacitance and inductance consider to be nearly zero,

If cable size 3or 4x 25sq.mm or larger then z=root(R square + X square)

so not only current rating of cable but also to consider voltage drop we have to design cable size.

Sigh

I guess that you do not know anything about the fundamental laws of electricity. From your question I can tell you know nothing about Ohm's law, the conductivity of metals and insulators, or even how to calculate the power released in a fixed resistance with a known current.

Ok, here's a layman's explanation.

The current limits you've found are the continuous current limits that these wires can handle at room temperature. At this current the power released per meter of wire by the resistance per meter of this wire will not cause the insulation around this wire to fail. Different cable constructions can handle higher amount of current before reaching an insulation failure condition.

Even before taking account of skin effect, the ampacity of a cable would relate to the cross-sectional area; i.e., proportional to d². However, the heat generated must be dissipated through the wire surface and the insulation, whose area is proportional to d.