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#123269 - 03/10/06 02:35 AM Joining Water and Electricity
RODALCO Offline
Member

Registered: 12/08/05
Posts: 863
Loc: Titirangi, Akld, New Zealand
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!! Water pipe straight through double orange ducts from roadcrossing to transformer.

Photo evidence speaks for itself.
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The product of rotation, excitation and flux produces electricty.

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#123270 - 03/11/06 04:04 PM Re: Joining Water and Electricity
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
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.




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.



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

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Let's face it, these days if you're not young, you're old - Red Green grin

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#123271 - 03/11/06 05:36 PM Re: Joining Water and Electricity
Mash Offline
Member

Registered: 09/15/05
Posts: 50
Loc: South Australia
How did the water pipe go through the electrical conduit, was it bored from the side?

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#123272 - 03/11/06 06:32 PM Re: Joining Water and Electricity
RODALCO Offline
Member

Registered: 12/08/05
Posts: 863
Loc: Titirangi, Akld, New Zealand
Correct!

Done with directional drill, then pipe pulled through afterwards when drill is retracted.
_________________________
The product of rotation, excitation and flux produces electricty.

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#123273 - 03/13/06 08:31 AM Re: Joining Water and Electricity
BElder Offline
Member

Registered: 11/03/04
Posts: 52
Loc: Paradise, CA. U.S.A.
Infamous Needle in a Hay Stack

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#123274 - 03/13/06 09:14 AM Re: Joining Water and Electricity
mbhydro Offline
Member

Registered: 02/21/03
Posts: 344
Loc: Winnipeg MB Canada
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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#123275 - 03/14/06 12:11 AM Re: Joining Water and Electricity
kiwi Offline
Member

Registered: 12/04/04
Posts: 347
Loc: christchurch new zealand
Could this fault have produced a "Step Voltage" hazard on the ground around it in wet conditions ?

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#123276 - 03/14/06 11:30 AM Re: Joining Water and Electricity
RODALCO Offline
Member

Registered: 12/08/05
Posts: 863
Loc: Titirangi, Akld, New Zealand
 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.

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#123277 - 03/21/06 11:03 AM Re: Joining Water and Electricity
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Some follow-up pictures:

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



The 4 core section damaged by the directional drill:

_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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