From LF to VHF it is ALWAYS power dissipated in conductor resistance
which limits the power handling capability of the line. Voltage has
nothing to do with it. Above VHF dielectric loss becomes be the
limitation.

Consideration of ambient temperature is vital. Are you located in
Alaska at midnight in mid-winter? Or are you in the New Mexico desert
in July, at noon. It makes hell of a difference?

With coax everything depends on the temperture softening point of
polyethylene and on the the longer-term temperature deterioration
(hardening, cracking, brittleness) of the PVC sheath.

Is the cable embedded in an asbestos insulated brick wall or is it
suspended in free air with a breeze in the shade? Or in sunlight?

The power rating data provided by manufacturers for amateur grade
coaxial cables is useless nonsense. From inspection of manufacturers'
tables (watts) it can be deduced their ratings are based on the
melting point of polyethylene. Salesmen's blurbs, no doubt plagiarised
in ARRL publications, sound very good in order to sell the stuff.

To gain an elementary understanding of what it's all about, download
in a few seconds, easy to use, practical application, small program
"COAXRATE" from website below and run immediately. (Not zipped up).

Program "COAXRATE".
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Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
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