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Discuss Fault on underground Sub Mains cable in the Electrical Forum area at ElectriciansForums.net

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Hi,

I am currently in the middle of completing a new installation in time for a Halloween event at a local activity centre. Over the weekend, while I was not there, it seems that they have lost power to the sub mains distribution panel.
Unfortunately I didn't have my Megger to hand yesterday as it is being calibrated, I will get it back later today, so I couldn't test the cable.
I have 400V across all three phases and neutral at the Sub station end, protected by 3 x 300A BS88 fuses. The 120mm 4Core SWA is buried direct in to the ground and runs 530m. At the other end it is connected in to a PowerPact panel. I have no voltage at the panel end. The fuse chamber was still in the on position at the sub station, but upon testing to see if I have voltage at the distribution panel end I only have continuity beep between all three phases and neutral.
I did notice that L1 fuse has blown, which I replaced yesterday but still no voltage.

I feel that the cable must be damaged underground, but I don't see how it can stay on at the fuse chamber? Any ideas?
I will be able to test the cable later today.

Also if it is damaged underground, does any one know of any tester out there to find the section of damaged cable, as its a 530m run and digging that back up will be costly!!
 
Yes I will be testing the cable later once I get my Megger back from the wholesalers. if the cable is damaged, which it must be, I can;t see why the fuse chamber stays ON and doesn't blow?
 
A bit of enthusiastic back filling is a likely culprit . What kind of spoil was the dig?
If you google 'Cat and Genny' you will get a load of specialists that do this , or you can hire the gear yourself.
 
Its quarry stone, backfield with a layer of sand the quarry stone. I didn't see the backfill myself, but that was over a month ago now. The cable past all tests then, IR, R1+R2, Zs, PFC, PSCC etc.
 
Hi,

I am currently in the middle of completing a new installation in time for a Halloween event at a local activity centre. Over the weekend, while I was not there, it seems that they have lost power to the sub mains distribution panel.
Unfortunately I didn't have my Megger to hand yesterday as it is being calibrated, I will get it back later today, so I couldn't test the cable.
I have 400V across all three phases and neutral at the Sub station end, protected by 3 x 300A BS88 fuses. The 120mm 4Core SWA is buried direct in to the ground and runs 530m. At the other end it is connected in to a PowerPact panel. I have no voltage at the panel end. The fuse chamber was still in the on position at the sub station, but upon testing to see if I have voltage at the distribution panel end I only have continuity beep between all three phases and neutral.
I did notice that L1 fuse has blown, which I replaced yesterday but still no voltage.

I feel that the cable must be damaged underground, but I don't see how it can stay on at the fuse chamber? Any ideas?
I will be able to test the cable later today.

Also if it is damaged underground, does any one know of any tester out there to find the section of damaged cable, as its a 530m run and digging that back up will be costly!!
 
Quarry stone will do it every time especially if there is activity on the made up ground.
Our cable crossing frequently gave as a firework display.
 
Good chance a sharp rock has travelled down and pierced the cable, the backfill will have been loose and settled , the rest with a bit of help from the traffic.

Obviously I will be able to tell later when I complete R1+R2 and IR tests
But it will still stay in the On position, do you think clean cut? Because I should have a least have 1 or 2 phases if partly damaged?
 

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