Testing breakage in cable

[arrie]

I've looked through the forum, but didn't come up with something similar.
Let's say you have a lead extension cable, for running 220V somewhere, where you need power, but have no plug. (Just to make it clear)
So one day this 30meter lead stops conducting, maybe even trips the power. The fault is not at the plugs, cable break somewhere, but the question is where.
You end up chucking the whole lead in the dust bin, because you do not know where the fault is.
What is the simplest way to determine where the break have occurred, as measured from either end?

I was thinking sending a signal(in form of pulse) down each line, when reaching the break, it should bounce back towards the start. Time its departure and arrival, divide by two. Now you have time and speed(at which your signal travels), so calculate the distance.
Is this possible without breaking the bank, or just possible at all?

Thanks for your time.

 

[Neal]

You can obtain hall effect based equipment, don't know if that is cost effective for your cable. You could always cut it in half or 2/3 and have one good cable. If there is only one defect place.

 

[arrie]

Yip, cutting it in half every time till you have many leads of many lengths that work can be an solution.
But unfortunately it's not the solution I was hoping for this time round.
I wanted to include it in my original post, but thought that people would kinda get the idea that was not what I was after.

 

[Neal]

Chech on the hall effect based testers, used thos to find microscopic opens and shorts on pcbs. Works real well. Check some electrical supplier for equipment for finding underground cable breaks ans shorts. Maybe someone has an old model he wants to get rid of, but would be ok for you

 

[ericgibbs]

Yip, cutting it in half every time till you have many leads of many lengths that work can be an solution.
But unfortunately it's not the solution I was hoping for this time round.
I wanted to include it in my original post, but thought that people would kinda get the idea that was not what I was after.

hi,
Commercial cable testers do work in that way.

Sharp pulse injected into the cable end, and measure the echo, knowing the transit time,
its possible to get the distance of the o/c or s/c.

They are not cheap..

Also you get devices you connect to the cable [low voltage] injects an alternating signal into the cable end.
The user has a receiver which he uses above the ground or along the cable[ bit like a metal detector].
He finds where the picked up signal disappears and digs a hole.

It may be possible to hire a cable locator for a one off job.?

 

[stevez]

Time domain reflectometer may be a good handful of words to google on. In one of my antenna books is a very simple pulse generator and the instructions on how to construct the generator as well as couple it to a scope so that the measurements you describe can be made.

 

[afesheir]

I have an idea used for checking old copper telephone cables ... this technique is called Varley loop test ...

see this: https://www.answers.com/topic/varley-loop-test?cat=technology

and for more info u can search on google bcz i didn't find suitable resource for u now ... but further search can result in better material ...

 

[JimB]

A time domain reflectometer is the way to go.

Comercial instruments are expensive, but if you have an oscilloscope, it is possible to make a cheap simple unit for a few pounds (dollars/euro/yen/ringit/dong/ w.h.y.)

JimB

 

[arrie]

Thanks guys.
I don't own a scope, as these can be R8000 to R20 000, heck you can almost buy a car for that price, an old car okay.
Anything equipment here is a bad idea, I looked into CO detectors the other day, R4500 to R15000.
That is a lot of my intestines being ripped out.
My logic also tells me to put a peaky pulse in the one end and time it coming back, or see if it arrives at the other end.
Sorry, no hiring of such expensive equipment here, because it's as expensive as buying the bloody thing.....almost.

Nope I will have to make it.
I have to go check exactly what hall effect is about.

 

[arrie]

I've quickly checked out cable testers from reputable dealers, varies from R11000 to R45000.
That's huge brew.

 

[gerty]

We use an inductive pickup tool (greenlee gt-11) and go down the length of the cable. The detector will stop chirping when you pass the break. If the break is on the neutral we disconnnect the cable ,both ends, and connect the neutral conductor to a hot lead via jumper wire to find it.

 

[john1]

Hi arrie,

Just seen your post:
https://www.electro-tech-online.com/threads/testing-breakage-in-cable.40636/

This has happened to me many times. I use extension leads a lot, and they have a rough life
with me, i am sorry to say.

Over the years i have found a couple of simple ways to deal with this.

The first way is to cut the cable. Have a really good look at the ends near the fittings,
these are the most likely places for a break, with the bonus that if a bit of damage near the
end gets cut, and its not the break, then youve only lost a short bit. Sometimes its worth
cutting a foot from each end, if its important not to shorten the cable much, this will often
clear the problem with minimum effort. One end at a time of course.
If its still got the break, then my next cut would be part way along, not half way i would go
with about a third. This method as mentioned, gives you two cables, the down side is finding
extra plugs and sockets for the remaining good bits.

Another way i have used many times is the good old bell-set.
Just a little bell and battery, connect it to each end of your faulty conductor, and wiggle
the cable through your hands working your way along. Hopefully the bell will sound if you
wiggle the faulty bit and get it to conduct.

Another way i have used is a spark. Causing a spark at the break can be entertaining. Takes
a bit of setting up, one problem is trying to hear it. If your break is wide, you may not be
able to use this method. I have used a buzzer and battery with a transformer to locate a
break in the past by waiting for the smoke from the spark to come from the cable. That was not necessary really, as i had by then located the whereabouts of the break cos i could hear
the spark, but allowing it to continue until it burnt through led me precisely to the break.

Another possibility that i have not tried is capacitance.
It might be possible to approximate the length of a conductor by its capacitance to the
remaining conductors. Maybe a wheatsone bridge arrangement. Or just a simple oscillator like
a "stylophone".
Or maybe the capacitance could be used externally, to pick up a signal along the conductor ?
Which would fade past the break ?

Or maybe injecting RF might give an increased radiated signal at the open end, i dunno but
it sounds possible. Someone skilled with ariels might know about that.

Best of luck with your cable checks, lets us know how you get on,
Cheers, John

 

[john1]

Still thinking about your extension lead.
The simplest way is often the best,
a very carefull examination by hand of the full length will most likely give you two or three
places that look and feel suspicious.
If i had to cut it, i would pick one of these places.

John

 

[arrie]

Thanks John.

Those are really practical tips. T
his is one of those cheaper three core cables, it seems the cores inside the main outer insulation have wound up or something, now the whole lead has a very loopy thing about itself, looks like those American fun rides with the corkscrew type shape.
I've contemplated chucking the whole thing, but then again it's a lot of lead wire for you. The plugs are cheap, so having some shorter leads will still come in handy for many applications.
I've tried the hand-held inspection approach, but must say, with all those corky twists its easy to get it wrong.
In any case, the poor lead is staring me in the eye every day, begging for attention, I'll then just stroke it a bit and reassure it that I'm looking for the better solution.

 

[RODALCO]

I use an electricians voltage "test finger" to check for faults in my christmas lights.
It stops beeping from where the open circuit appears.
In your case you may have to liven one core at the time and earth the other two cores to avoid capacitive readings.
Where the beep stops the open break usually is.

As others already said 90% of breaks are within 5 to 10 cm from the plug ends from where the leads are flexed a lot.

 

[mneary]

If there's a problem near the ends it is easily found and repaired. If there's a hidden quality problem somewhere else, there may be more than one.

 

[arrie]

Thanks rodalco and mneary.

I suspect more than one problem in the cable, it's given me enough grief now, so I decided to just take the two plugs of and chuck it, will buy new extension cable and make a new lead.