In article ,
JS wrote:

Hmmm. Yes. :-)

I was hoping to use a compass deflection as a way of telling how much
heat/power was being lost in neatly wrapped coiled of mains flex.

Surely there is a loss of something due to the neatness - or perhaps
not?

Lower probability of managing to "accidentally" trip an unwanted
in-law over the mounds of loose cable lying around on the floor? Some
would call that a significant loss :-)

Semi-seriously, though - I believe that the actual power loss in the
wire, and thus the total amount of heat generated, is as close to
identical in the two cases as makes no difference.

The reason for not coiling up high-amperage mains cable is probably
one of heat dissipation, rather than heat generation. If the cable is
lying out in a straight line, or just piled up loosely, it can shed
the waste heat effectively via radiation, conduction to the ground,
and convection into the air. If you coil it up on a spindle of some
sort, the heat generated in the inner turns of the coil will have no
easy means of escape... it can only get out via conduction through the
outer turns of the coil, which are rubber- or plastic-insulated and
thus have a high thermal resistance.

Run 20 amps through a heavy-duty extension cord, lose a few volts due to IR
drop, and you can end up with quite a few tens of watts of heat to be
lost. Under prolonged load this might, perhaps, be enough to affect
the integrity of the cord's insulation somewhat, or even cause a
thermal burn.

--
Dave Platt AE6EO
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