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Joined: Dec 2005
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RODALCO Offline OP
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Photo's will be posted of this cable fault.

Today 10th Mar 2006, I had to locate a cable fault on a 4 core Al 185mm² at 4222 Great North Road Glendene, which also affected my favorite Italian Pizza shop. A generator was put in place to get power going prior to me locating the actual fault due to the 33 kV fault on the North Shore which had more priority.

Digger opened up hole, Jackpot!! [Linked Image] Water pipe straight through double orange ducts from roadcrossing to transformer.

Photo evidence speaks for itself.


The product of rotation, excitation and flux produces electricty.
Joined: Jul 2002
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Pics and info:


Quote
The council is upgrading the older water mains at the moment.
By drilling for a the new water mains at 4222 Great North road Glendene, the drilling contractor had the power marked out by the POCO.
but, he didn't mark the road crossings,
and
Jackpot!!
Fizzle and crackle,
Some people had lost power or had only 1 Phase.

Power was not lost immediately when the cable was hit but it lasted for nearly 2 weeks and a bit of rain, triggered all the events.

The 200 kVA supply transformer was across the road.

Cable damaged was 4 core Aluminium 185mm².

[Linked Image]

Better view, when digger opened up the hole.
Note the thin black cable was a Telecom cable That cable got nicked by our digger operator so we called Telecom to fix it.
no marker strip was put in place.

[Linked Image]

Closer up of ducts. Not sure what is in the white pipe. That may be the older watermains.
Both black cables are Telecoms.

[Linked Image]

Joined: Sep 2005
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M
Member
How did the water pipe go through the electrical conduit, was it bored from the side?

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RODALCO Offline OP
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Correct!

Done with directional drill, then pipe pulled through afterwards when drill is retracted.


The product of rotation, excitation and flux produces electricty.
Joined: Nov 2004
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Member
Infamous Needle in a Hay Stack [Linked Image]

Joined: Feb 2003
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Member
Does other areas hydro vac the utility crossings to expose (pothole) them before directional drilling?

Not sure if its Manitoba law dealing with underground structures, but I see more of the suction trucks prepping the route with potholes before the drilling begins.

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K
Member
Could this fault have produced a "Step Voltage" hazard on the ground around it in wet conditions ?

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RODALCO Offline OP
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Quote
Does other areas hydro vac the utility crossings to expose (pothole) them before directional drilling?

In this case the utility mains and telephone were marked out. I think the cable marker missed the roadcrossing. Quite often an area of 1 km on both sides of the road has to be marked at out at once, which is quite a big task. The UG drawings should be used as well by the drill contractor too to confirm prior to drilling. These drawings sometimes have errors in them too, and a cable gets hit.

Quote
Could this fault have produced a "Step Voltage" hazard on the ground around it in wet conditions ?

Good point KIWI, In this case it's a 3Ø400 Volts mains cable. At a depth of 600 mm there is some chance of a step voltage although it depends upon ground resistivity which is even in wet conditions quite high.
Bear in mind all the LV faults 'cooking' away and have not been marked out yet or haven't caused any phase loss yet.
I have not heard of any one being 'zapped' by a faulty cable below ground yet.

In case of HT it's a different scenario.
These cables have an earthed screen around the cable which will take the fault current and trip the earth fault relay.
For a brief period, during the fault, there will be a rise in potential at the fault area, although most will taken back to earth through the cable screen. These faults usually don't cook for days and blow out instantly.

edited for typo errors


[This message has been edited by RODALCO (edited 03-14-2006).]


The product of rotation, excitation and flux produces electricty.
Joined: Jul 2002
Posts: 8,432
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Some follow-up pictures:

The actual "hit cable" Close Up view.
Red Ø and Neutral completely gone:

[Linked Image]

The 4 core section damaged by the directional drill:

[Linked Image]


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