Manufacturers' and handbook recommended maximum power ratings for coax, for
amateurs, are based on the MELTING (FAILURE) POINT temperature of
polyethylene. Nobody in their right minds would ever run common-or-garden
RG-58, for example, at such a high power input. Not even at the North Pole.

Within seconds, just to grasp the cable in the palm of the hand, would cause
blistering of the skin.

In any case, the power dissipated in the cable would not be tolerated by
amateurs because of the loss in signal strength.

Also, running the cable at such a high temperature severely reduces the life
of the PVC outer jacket. It soon becomes brittle and cracks. With time it
fails before the coaxial polyethylene insulant.

Of course, the high advertised power ratings are advantageous to technically
ignorant USA cable sales departments and salesmen. It just looks good in
the sales literature.

Rest assured, NASA never uses RG-58 at one kilowatt, not even with an SWR of
1-to-1. Their missions last longer than 10 minutes. ;o)
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Reg, G4FGQ