How much current does is take to melt a cable?

Well if you run a cable in a way that the heat cannot escape - coiled or lagged, then the rating is reduced, if the load is on for a long time - but long is many tens of minutes to hours depending on the mass to be heated.

Melting the plastic means it has got well above 100C, as PVC will stand that all day, it just tends to stretch and tear if flexed or compressed while that hot and if you do it a lot  it loses its flexibility. In contrast normal ratings assume the copper is o hotter than 70C. That gives a predicted cable life of many decades.

Now to melt the copper smartly  is more  difficult than the plastic and needs hundreds of amps for a a single strand of 2.5mm

So was the coiled section of cable the bit that melted, or was that OK ? If that is OK we can rule out overload as the issue.

If a short section near a termination is toasted, then that tells us that termination was not connecting to all the strands well, maybe some missed the screw, or the terminal was dirty or oily.

A burnt earth suggests either it is badly wired and that is not the earth or there has been a serious fault.Even so, if only the end is damaged, there was a termination issue.

Or perhaps a whisker of stray copper bridging to another core, now blasted away, hiding the evidence.

If you can post a pic or two we can probably have a more informed best guess.

Mike.

Well if you run a cable in a way that the heat cannot escape - coiled or lagged, then the rating is reduced, if the load is on for a long time - but long is many tens of minutes to hours depending on the mass to be heated.

Melting the plastic means it has got well above 100C, as PVC will stand that all day, it just tends to stretch and tear if flexed or compressed while that hot and if you do it a lot  it loses its flexibility. In contrast normal ratings assume the copper is o hotter than 70C. That gives a predicted cable life of many decades.

Now to melt the copper smartly  is more  difficult than the plastic and needs hundreds of amps for a a single strand of 2.5mm

So was the coiled section of cable the bit that melted, or was that OK ? If that is OK we can rule out overload as the issue.

If a short section near a termination is toasted, then that tells us that termination was not connecting to all the strands well, maybe some missed the screw, or the terminal was dirty or oily.

A burnt earth suggests either it is badly wired and that is not the earth or there has been a serious fault.Even so, if only the end is damaged, there was a termination issue.

Or perhaps a whisker of stray copper bridging to another core, now blasted away, hiding the evidence.

If you can post a pic or two we can probably have a more informed best guess.

Mike.