Underground Cable Fault

Hello,
Working on a project at the moment where a newly laid underground swa cable 300 metres long ,3 X 35mm squared appears faulty and is giving some unusual readings on
insulation resistance tester, 1000 volt dc test voltage.
The readings are as follows:
Armour - Earth core >2000Mohms-ok
Armour - Blue core 1000-2000ohms
Armour - Brown core 1000-2000ohms
Earth core - Blue core >2000Mohms-ok
Earth core - Brown core >2000Mohms-ok
Blue core - Brown core 1000-2000ohms

Cable buried 1 metre deep in sand.Is it possibly faulty manufactured cable. Should have meggered it b4 laying it.Would 1000 volt dc test break down fault to a dead short.Tried reflectance but no good as it requires a dead short or open circuit to determine location of fault.Any help
Conclusion:
Earth core ok.Armour,brown and blue all problem.

1KV breakdown test may or may not break down to a dead short. Probably a knick in the insulation. Apply voltage to cable. Probe Earth surface at various points. You should read highest voltage at point of fault.
If not, then cable itself is faulty.

... sorry to be pointing out the obvious but have you taken off the heat shrink boot at the other end of the cable!!!

What type of cable exactly? What is the insulation system?
Most cable manufacturers extensively test cable before shipping, and the testing will show even minor faults in the insulation system almost 100% of the time.

Most failures are due to field failures, including improper installation, improper termination, or pure mechanical (physical) damage, such as dropping a reel and crushing a section or exceeding the design bend radius.

A 1KV tester won't show a whole lot about the fault, but one that seems that severe indicates to me that it is most likely in one place. Check the terminations to start (each end) carefully (and yes, check the boots at each end if installed). If you can, get your hands on a TDR (Time Domain Reflectometer) type of tester (Example) to try to locate the distance to the fault. If that shows something, dig up that area very carefully. Breakdown tests at the factory are usually done with a very high voltage corona-discharge test, most commonly AC, though DC tests are still run on some constructions.

You might also want to contact the manufacturer of the cable, as most manufacturers of high-end cables have guarantees on the cable.

Is this a genuine problem or some sort of test question for an exam, sounds like a typical City and Guilds 236 exam question to me ?

Either way, did the people who laid the cable not provide test documents, i am sure they did not just dump it in the ground and walk away ?

how much voltage you want to pass in that cable????
so that we can decide he breakdown strengh ogf the cable with your resistance reading...

THE VOLTAGE IS 230 VOLT AC RMS.CABLE IS RATED FOR 1000 VOLTS.
cable compromises pvc outer sheath, then steel wire armour, then xlpe(cross linked poly ethylene),then 3 pvc insulated cores.
Tried time domain reflectance but no good as it requires a dead short or open circuit to determine location of fault.Even got a guy from esb who does nothing else but detect faults on the utility underground high tension system.He applied megger test @ 5 kv dc to try and break down the fault to a dead short but to no avail.From his experience all was pointing towards a manufacturing problem, which he has come across b4.Tried applying voltage and drew 20 amps for 5 mins ,following day mcb was tripped.THIS IS REAL WORLD AND CUSTOMER REALLY BOILED!

jimlong said:

THE VOLTAGE IS 230 VOLT AC RMS.CABLE IS RATED FOR 1000 VOLTS.
cable compromises pvc outer sheath, then steel wire armour, then xlpe(cross linked poly ethylene),then 3 pvc insulated cores.
Tried time domain reflectance but no good as it requires a dead short or open circuit to determine location of fault.Even got a guy from esb who does nothing else but detect faults on the utility underground high tension system.He applied megger test @ 5 kv dc to try and break down the fault to a dead short but to no avail.From his experience all was pointing towards a manufacturing problem, which he has come across b4.Tried applying voltage and drew 20 amps for 5 mins ,following day mcb was tripped.THIS IS REAL WORLD AND CUSTOMER REALLY BOILED!

Click to expand...

I have ran overhead (temp) exposed wire before when the construction crew hit a main feeder with a jack hammer, nice blow-up followed. We started running the overhead temp cables while crew started diggin up and running new cables and conduit.
If your customer is at the boiling point, this will get production going again but it'll cost him!!

Cut the cable in half and test both halves. If you get the same problem in both halves, then you know the problem is with all of the cable. If not, then you know which half to replace. Repeat until the economics of digging/splitting/joining outweigh the cost of replacing the remaining length of cable.

Please dont do anything,
you can go ahead to claim on manufacture or vendor...
Just replace the cable instead of losing time on behind it.
Thanks in advance for your understanding.
Naag.