How to calculate effective thermal resistivity??????

Yes.

Contact BICC Cables and ask about their Electric Cables Handbook. This is a link to the people who bought BICC Cables.

www.generalcable.com/GeneralCable/

In theory, there is no thermal limit to the conductor; it is the insulation/ construction that limits the current carrying capacity.

You've obviously never been standing next to me when I melted copper. Oh, yeah! The insulation goes away first, but the copper will follow.

You forgot something- the insulation of bare wire (copper in your case) is the surrounding atmosphere, isn't it? Also, some of this discussion, as I stated, is theory. As probably in your case, I mainly concern myself with the real world. However, most of Ohm's Law etc. is theory, as is the whole world of EE, if you get detailed enough. Look at Superconductors, chilled w/ liquid N2. Finally, the insulation in your example has caused the copper to greatly heat as it was melting off.

Yes, all of EE is theory, but it is also mostly fact. Ohm's Law is both a theory and an observed fact. You can take an ordinary copper cable and calculate the temperature rise (and gradient across the insulation as part of that) with an FEA program and then hook a piece of cable just like that to a generator and measure it, and you'll get agreement within the experimental error. I've done it many times for electric railroad power bonds.

The complications only arise from the physical complexity (i.e. part of the cable runs near a ventilation louver rather than in still air, or some workman work hardened the cable when he bent it nine times while installing the terminal lug, and so on).

People who do this as a business (like General Cable) know and publish all this info. There's not much mystery, unless you just don't look at their data.

Hi,

better to measure yourself as thermal resistance is very much dependant on cooling condition of outer surface.

Put a known thermal loss into your cable by simply current and resistance you will know. This may be as small as 1% of later load if temperature measurement is sensitive.

Measure inner temperature rise after switch on/ switch off.

Either take the changing resistance of the copper (near 0,4%/K) as temperature indication or put in a separate small, sensitive and accurate temperature sensor inside if there is space available and distortion is not too big by changed geometry.

Do this in a geometry of cable attachment as you will use your cable but at a situation (clamping?) that has worst cooling.

RHABE