[daemoncoder]

I found the break in a 10m extension cable, by measuring the capacitance at each end and calculating the ratio of the two values. This predicted a break at roughly 1m from one end. Then started probing the cable from 10cm towards the ”short” side, moving towards the long side. Found the break within 15cm, saving roughly 9m of cable.

[dr_orpheus]

That's pretty clever. Also if you are interested (not 100% applicable because it's not something most people can do at home) there is a practice for finding breaks/partial breaks in cables using time domain reflectometry (TDM) [0]. You send a pulse in to one end of the cable and measure how long it takes for some reflected energy at the break to return. It's pretty cool stuff and you only need access to one side of a cable. I have used this in my job for finding discontinuities in large RF cables.

If you do have some electrics equipment at home (o-scope, sig-gen) you can make do it yourself [1]

[0] https://en.wikipedia.org/wiki/Time-domain_reflectometer

[1] https://www.allaboutcircuits.com/projects/build-your-own-tim...

[b06tmm]

We did this in the Navy to check circular wave guides to the ECM antennas in the leading edge of our bombers wings. We had to do this once every 6 months (I think) with a sweep generator to see if the cables needed to be replaced. Also, installing these were a complete PITA! Nothing was a straight run to where it needed to go, so you had to bend them as gently as possible as you fed the new line into the wing. Then you had to test it again.

These were very expensive and I've seen more than a few screwup's while installing them.

A coworker's cat-5 tester also has a TDR function that shows you where an issue is on the line.

[tech2]

Many _many_ years ago we used to have to do that on occasion in our office to find where the break in the coax network was. That brought some amusing memories back for me, thanks :)

[daemoncoder]

I got the capacitance idea from having worked with TDR in the late 80's. As students we used them to tune FM antenna combiners, but I never quite got the hang of it at the time.

[robocat]

Unless there was an obvious reason for the break then there could easily be another "nearly broken" fault in the cable e.g. if break was due to stretching.

A partial break has the risk of local overheating.

So perhaps you should biff the cable anyway if it is likely to be unsafe?

[daemoncoder]

This is a good point - the cable is probably 20+ years old and has been used for weed eaters and lawn mowers. It's been regularly uncoiled and re-coiled, not always correctly.

The correct way is using the over-and-under technique: https://www.popularmechanics.com/home/tools/a15873/over-unde...

[emilfihlman]

Now that's pretty sweet!