Four core Power Cable Short Circuit

[hhhunzai]

Hello Everyone!
Refer to the subject, please guide me in a situation, there is a power cable 25sq. mm, 4 core pvc/pvc non swa buried directly in ground and in some ducts.The cable has damaged anywhere and it shows short circuit between every conductor.I have tested with a uni-T multimeter, it shows almost 2 to 3M ohms resistance between each conductor.The operating voltage is 3 phase, 415volt, 50Hz

Please suggest me a technique to sort this short circuit out, without digging the all area and ducts in ground.Is it possible to locate the exact location of the leakage area?

Your opinions are requested in this regard

 

[Engineer54]

If your getting 2 or 3million ohms between the conductors, where the hell is your short circuit??

 

[hhhunzai]

If your getting 2 or 3million ohms between the conductors, where the hell is your short circuit??

yes your are right, but it shouldn't show this resistance too it should show infinity.
As I am checking this cable with a "Multimeter not with a Megger, With magger I think it will show a lower resistance.
Multimeter has a low voltage and megger test is about 1000Vlots.

 

[ruston]

Well if it is indeed a short the first thing to do is walk the length of the cable and look for intrusions and disturbances, presuming you know the run .

 

[hhhunzai]

Well if it is indeed a short the first thing to do is walk the length of the cable and look for intrusions and disturbances, presuming you know the run .

As I have mentioned in my First post, I want to know a technique, if there is one; to detect the problem without digging the ground. It an underground buried cable, almost 2.5 feet under the ground surface.
Is it possible by energizing the cable and then check with tool, like a meter or something else.

 

[wildgoose]

I'd be inclined to insulation test it again using at least 500vdc with a known good and calibrated meter.

A dig-up is rather a big decision to make from the readings off a multimeter !!!

 

[Engineer54]

yes your are right, but it shouldn't show this resistance too it should show infinity.
As I am checking this cable with a "Multimeter not with a Megger, With magger I think it will show a lower resistance.
Multimeter has a low voltage and megger test is about 1000Vlots.

Then why pray are you using a multimeter, when you should be using an insulation tester?? Use the right tool for the Job. You will then KNOW that you have a problem!!!
The only way your going to find a fault on any buried cable is by use of test kit that can see/locate a high resistance point and give you a distance from the testing position. As you don't even have an insulation test kit, i'm pretty sure your not going to have fault location test kit!! So if there are no physical/visual indicators as to where the fault could be, your pretty stuffed i'm afraid!!

I misread your original post, i thought you were referring to a multi function meter!!

 

[hhhunzai]

I'd be inclined to insulation test it again using at least 500vdc with a known good and calibrated meter.

A dig-up is rather a big decision to make from the readings off a multimeter !!!

You got my point, but I have just a multimeter right now. I am sure enough about what I am saying. I have performed such test before and the problem was cable insulation leakage, not complete short but due to moisture and a minor leakage in cable this make breakers to trip.
So the point is, Is it possible to detect this leakage with a tool, I think there should be?

 

[ruston]

Sorry had to go, if you walk the length you may be able to see where the damage has occurred . You could hire a Cat and Genny or a Wheatstone bridge to find the fault if you have one.

 

[wallyanker]

Would something like this do the job??

Megger TDR500 Cable Fault Locator - Megger QualiFyr TDR500 - Time Domain Reflectometer

 

[hhhunzai]

Sorry had to go, if you walk the length you may be able to see where the damage has occurred . You could hire a Cat and Genny or a Wheatstone bridge to find the fault if you have one.

I will make it by myself, I have the idea about this bridge, just tell me how I can perform test with Wheatstone bridge.

 

[hhhunzai]

Would something like this do the job??

Megger TDR500 Cable Fault Locator - Megger QualiFyr TDR500 - Time Domain Reflectometer

It would be a good idea but its expensive here in our country.
Please suggest me an idea that would be easier and affordable for me.
I wan to make it by my self, with a Wheatstone bridge.

 

[ruston]

http://www.ceh.org.uk/docs/manual/O20001.pdf
http://www.ceh.org.uk/docs/manual/O20001.pdf

I have included the user instructions for the Cat/ Genny and the Wheatstone bridge. The Cat and Genny should be the easiest for you as it has a signal generator.
The Wheatstone bridge is easier to use if at least one of the cores are intact. Simplified it measures the resistance equally along the length of the cable using either one of the intact cores or a separate cable connected to the suspect core. the readings are calculated as per the chart supplied with the tester and should be accurate for about a metre. Forgive me if I have got it wrong Lads it's been a long time.

 

[Knobhead]

With 3MΏ at 415 V I’d be inclined to just switch it back in to service. If it holds then OK, if it blows you will have a better (lower) fault reading. You really can’t do fault finding of this type with a multi meter. As to the Wheatstone bridge 3MΏ is to high for it to work.

 

[needasparks]

The OP said this is an un-armoured cable so i would guess it would have had some damage all along it caused by pulling it in the duct being a 25mm 4core, there not light.

 

[hhhunzai]

With 3MΏ at 415 V I’d be inclined to just switch it back in to service. If it holds then OK, if it blows you will have a better (lower) fault reading. You really can’t do fault finding of this type with a multi meter. As to the Wheatstone bridge 3MΏ is to high for it to work.

As you have suggested to switch it back, It was already working but sometimes it makes problems, either due to moisture or or any thing else.
there were two cables with same ratings and cores, one is working with showing infinity resistance and the other is showing 2 to 3M ohms.
I have,t checked with a Megger or cable tester.
You make me understand about Wheatstone method I will try to figure it out by myself.

 

[hhhunzai]

The OP said this is an un-armoured cable so i would guess it would have had some damage all along it caused by pulling it in the duct being a 25mm 4core, there not light.

This cable was working from last three years.
now it is creating troubles, the breaker do not trips every time but two or three times a day. There were two cables with the same specification 25 sq mm, 4core connected to same breaker, and delivering power to a same panel.
One is working now and breaker do not trips after removal of other cable.
Now I have to trace its fault, have to locate the exact location were the problem is.

 

[Knobhead]

A Wheatstone bridge will not work. You don’t have the basic equipment needed for the tests and I seriously doubt the knowledge needed to interpret them if you did. Call a local electrician before you hurt yourself.