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PostPosted: Tue Apr 20, 2010 3:41 pm 
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Joined: Fri Apr 09, 2010 12:23 pm
Posts: 3
Location: Hobart
I need to clear a 300+ metre winding driveway through a thickly wooded block to my building site. All services are available at the boundary, water, power and phone and I would like to know if I can put them all together in a trench under the road then surface it. I'm baulking at the massive cost and work involved and hope this can kill 2 birds with 1 stone.


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PostPosted: Tue Apr 20, 2010 4:31 pm 
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Joined: Tue Jun 14, 2005 10:08 am
Posts: 32
Location: Macedon Ranges (Vic)
Yes all the services can go in the same trench.

There are requirements for minimum separation between the services.

Take a look at the trenching requirments pdf file that can be found at: http://www.telstra.com.au/smartcommunity/mybuilder.html


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PostPosted: Tue Apr 20, 2010 7:42 pm 
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Joined: Fri Apr 09, 2010 12:23 pm
Posts: 3
Location: Hobart
Thanks for the link and the quick reply (50 minutes) to my first ever post.
Plenty more questions to come.


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PostPosted: Mon Apr 26, 2010 10:39 am 
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Joined: Fri Jan 18, 2008 2:46 pm
Posts: 320
Location: wycheproof
just be careful if they ever need to get to those pipes it means your driveway will be smashed up to repair the pipes but good luck also a trick our electrician told us was once the pipes wires cables are laid put a couple of inches of sand on top of them then later when your digging for something if you hit sand you know you are close to services and can stop digging


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PostPosted: Sat May 01, 2010 7:24 pm 
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Joined: Sat Dec 10, 2005 2:12 pm
Posts: 14
Location: Adelaide, South Australia
Having a 300 metre electrical service can cause voltage drop problems if not designed correctly. If using 100m cable rolls, connections will need to be done in the trench. Make sure your sparky knows his business- some mistakes can occur years later.
I'm a retired sparky.


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PostPosted: Sun May 02, 2010 1:10 pm 
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Joined: Fri Apr 09, 2010 12:23 pm
Posts: 3
Location: Hobart
Thanks mate, I was told I may need thicker cable to allow for this.
Someone said his cable laying worked out to $27 per metre but to budget for up to $35 for thicker cable.
Not sure if he meant that was the total connection cost including conduit.
Will I be allowed to do any of this myself or is that strictly an electricians job?
I think the actual length will be closer to 400m translating to $14000 for power connection.


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PostPosted: Fri May 07, 2010 3:59 am 
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Joined: Sat Dec 10, 2005 2:12 pm
Posts: 14
Location: Adelaide, South Australia
Gidday pauliebokbok.
Most certainly you will need "thicker cable", but thicker than what. The choosing of the cable size (goes by the cross-sectional area of the cable, i.e., 1.5sq mm, 2.5sq mm.....25sq mm and upwards), depends on the anticipated current drawn by the home, and the total resistance of the supply cable. It is a process that works backwards. The SAA wiring rules give the maximum voltage drop allowed (it was 12% of source supply, but it may have changed), then you refer to tables within the SAA wiring rules text book that give the resistance (per 100m) of cables. Working out the resistance of 300m, you then multiply this value by the anticipated current to be drawn, to give a result of what the voltage drop will be over the supply cable. If the voltage drop is too high, you then go to the next size cable, do the calculation again, and so on, until the voltage drop is within specs. It sounds difficult, but it isn't. It's just an application of Ohm's Law. You may be able to find the info on-line.

As to doing your own cable laying, most sparkies wouldn't mind. I wouldn't have. Things to look out for are the correct cable size, the size of the conduit to be used, the depth to which it must be buried, what will cover the trench, other services within the trench, etc. (again, this info can be found in the SAA rule book). Any connections within the trench (if using 100m roll cables), should be done by your sparky.

Cost-wise: mainly cable and conduit, plus trench digging.

Hope this helps.

doggy.


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PostPosted: Tue Jun 22, 2010 9:45 pm 
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Joined: Thu Jul 09, 2009 4:18 pm
Posts: 7
Location: central vic
the cable size will be very large.
a typical house would use 16mm2 but you will be more likley to need 90mm2 or greater.
the calculation is done using a formula using mV/Am, which is millivolt drop per ampere metre. your electrical contractor can work this out.
you will not have joins in the cable as it will be xlpe and vou can buy it in over 2000m roles but is expensive.


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