I'm wanting to replace the flex in a V old inertia reel electrical lead.
Existing flex is 3 core, 1.5 sq.mm (ish), rubber and is string filled. I
presume the string takes some of the strain off the cores. An invaluable
tool for me in the workshop but now the flex is showing some signs of wear.
The device is probably 70 years old [1], doesn't use slip rings but an
ingenious mechanism of pulleys to spool the flex onto the drum. I've been
using it daily for about 35 years. At full stretch of 12m, the pull required
is quite vigorous. I suspect modern standard flex would not put up with such
for too long. It is only employed for light loading only.
Have goggleyed a bit but no joy. I hope you knowledgeable folk may be able
to steer me in the right direction.

Many thanks
Nick.

[1] I removed this from an English Electric mobile generator that was used
to power searchlights during WWII. This cable reeler provided power to an
inspection lamp that would reach anywhere within (and some distance beyond)
the 36ft trailer.