# Forum Home Renovation Electrical  Max distance of underground 240v cable

## paddyjoy

If you wanted to build a house that was 750m from the nearest power source/street, would it be feasible to run 240v this distance underground or would the voltage drop be too much? Assuming the house would be using no more than 100 amps. Would you need an extra large/extra insulated cable or special insulation in the trench? 
This is totally hypothetical, just wondering what's feasible. 
Thanks!

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## koshari

feasibility is directly related to the size of your pockets. 
and 100Amps is quite significant, most domestic maximum demands will be in the vicinity of 60-80A 
i suspect you would be looking at well over 120mm2

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## Bruiser

Assuming 63A, 3ph, buried direct at 600mm you'll need 400 sq mm cable.  $$$.  Almost everything in life costs $100/m...

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## paddyjoy

:Roflmao:  
Thanks guys, I tried to work it out using AS3000 but the tables don't go beyond 95mm2 and even that was giving me a 17% voltage. 
So options are 
1) Massive cable, budget $100k
2) Get the overhead wiring extended into the land if that is even possible? $$$
3) DIY power through a genie of some form?

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## koshari

i suspect with that distance from the pole you are rural,  
therefore you will likely have a higher voltage feeder and can then have a transformer closer to the house. 
run some XLPE closer to the proximity. 
hell of a lot cheaper than running LV from the pole.

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## Bruiser

Agree - extending the overhead line is going to be the cheapest option.  The utility should provide you with a quote for this.

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## paddyjoy

Thanks guys, seems like I will need deep pockets either way. I have always wondered why people with huge acreages build their houses beside the road and don't set them right back to maximise the privacy, now I know why  :Smilie:

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## chalkyt

Big cables isn't my field but if you can get hold of AS3008 Electrical Installations-Selection of Cables,you will find heaps of information on cables from 1sq mm to 500+ sq mm. 
You can then play around with options re cable type, insulation, Copper, Aluminium, underground, overhead, voltage drop, etc. It will probably do your head in but at least you can talk some sense to a contractor. As the others have said... big cables = big bucks.

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## Bros

> You can then play around with options re cable type, insulation, Copper, Aluminium, underground, overhead, voltage drop, etc. It will probably do your head in

  That's why I didn't reply as I had a look at AS3008 and said to myself do I need this? so I went and did something else.

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## Uncle Bob

Out of all the cabling options, I'd say it would be cheaper to go off the grid solar, but then I remembered you wanted 100 amps  :Eek:

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## Smurf

Assuming it's a reasonably normal house then there are two sensible options: 
1. Extend the overhead HV line and install a transformer near the house. Talk to the power distributor in your area about this to find out cost etc. 
2. Go off-grid solar for electricity. Use LPG for cooking and to boost the solar hot water. Either LPG or a wood fire for heating (in most cases wood will be cheaper to run).  
So far as going off-grid is concerned, it's less hassle than you might think. The solar system will give you "normal" electricity for your appliances etc just like mains power does.  
LPG is less hassle than you might think too - you either have two big bottles and the gas company will swap them over for you when one is empty or alternatively you have one bigger one that is refilled on site when it gets low. Either way, you don't have to get the bottles filled yourself etc because they do it all for you. LPG in rural areas is, however, considerably more expensive than mains gas in the city (hence the wood fire to cut down on gas usage).

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## paddyjoy

I love the off grid idea but can you reliably go totally off grid? Are there many people doing this? I wouldn't need 100amps, my logic was that if I was going to dig a 750m trench I would make sure to build some redundancy in there for the future.

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## oldtrack123

> If you wanted to build a house that was 750m from the nearest power source/street, would it be feasible to run 240v this distance underground or would the voltage drop be too much? Assuming the house would be using no more than 100 amps. Would you need an extra large/extra insulated cable or special insulation in the trench? 
> This is totally hypothetical, just wondering what's feasible. 
> Thanks!

  Hi
We had a somewhat similar situation,[350M run length] but went 3phase .you then spread the load current over the 3phases 
Cables still have to take into account voltage drop but obviously smaller, easier to handle into conduit
Also has the advantage that we can use a heavy duty single phase 415V welder 
& 3phase devices/ motors [Saw bench] 
PeterQ

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## BRADFORD

A properly designed stand alone solar system is very reliable, and there are thousands of remote 
properties etc running on them.
You would need to look at all the alternatives and if grid connection comes close to the cost of solar I would 
go with the grid.
There is a running cost with solar (battery replacement) but this cost is minimal compared to diesel gen sets etc.
however compared to the grid power it is about the same (depends on usage).
I don't know how remote an area you are in, but many country areas are supplied by SWER lines which means a transformer at your house, this a good way to get power to more remote areas cheaply.
It works very well, I've been on one for over 20 years.

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## SilentButDeadly

Unless you can manage your house with a power consumption of not much more than 10 kwh per day then an off grid power supply is probably going to be more expensive (currently) than a SWER line and a transformer. The battery requirements to give you autonomy during 5 days of overcast weather/no wind will be expensive as will the back-up generator if you try an reduce that autonomy period or maintain a higher daily consumption.

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## koshari

are there 2 wires or one on the feeder that you will be ultimately connecting to,  
if there are 2 you may even have a 22kv feeder so you could go ABC from the feeder to a local pole with tranny, little bit less 3rd world than a swer. 
by the way i dont know what the bushfire royal commission outcomes are if your in Victoria but you could find you may even need ABC on a swer these days.

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## paddyjoy

> Hi
> We had a somewhat similar situation,[350M run length] but went 3phase .you then spread the load current over the 3phases 
> Cables still have to take into account voltage drop but obviously smaller, easier to handle into conduit
> Also has the advantage that we can use a heavy duty single phase 415V welder 
> & 3phase devices/ motors [Saw bench] 
> PeterQ

  I assume you had 415V running in the street and didn't need a transformer? Do you mind telling me how much it cost you "ball park" to go 350m?   

> are there 2 wires or one on the feeder that you will be ultimately connecting to,  
> if there are 2 you may even have a 22kv feeder so you could go ABC from the feeder to a local pole with tranny, little bit less 3rd world than a swer. 
> by the way i dont know what the bushfire royal commission outcomes are if your in Victoria but you could find you may even need ABC on a swer these days.

  I haven't bought anything yet, just doing some long term planning  :Smilie:   Will probably buy the land and then not build for 5 years or so. The particular one I'm interested in is only a few km's from the town and looks like it has an 11kv line running about 750m from the site, based on some googling I did I think it is 11kv.   
Currently we are using about 11kwh per day for 4 of us but if you were building a house from scratch I assume you could make it more energy efficient.

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## oldtrack123

Hi Pddy 
 Yes 3phase ran along the road
We were a bit lucky as a contribution charge for its erection had just expired
This was way back in1984 & the costs,  for that 350m part, to me was simply cable, conduit,  hire of  a trench digger
But I simply do not remember the cost. 
PeterQ

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## mattski2008

If you go for the overhead service extended on your property you will own and therefore be responsible for maintenance on all poles and lines on your property. The Electrical entity will only be responsible for the line from the tranny to your first pole.

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## oldtrack123

> If you go for the overhead service extended on your property you will own and therefore be responsible for maintenance on all poles and lines on your property. The Electrical entity will only be responsible for the line from the tranny to your first pole.

  Hi 
Tthe same applies if it is run underground!!!  
PeterQ

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## Smurf

> Unless you can manage your house with a power consumption of not much more than 10 kwh per day

   Excluding heating and hot water, average consumption with no special measures taken is around this value. Take out cooking (use gas) and use CFL/LED lighting and it becomes pretty easy to keep consumption down. 
As for how well it works, well I'll simply say that here in Tasmania (where the climate isn't exactly favourable to solar) we're quite successfully using solar to control the headworks of real, large grid-feeding power stations and those solar systems are stand alone (no backup). Likewise there's everything from road signs (about 600 of them) to houses running on stand alone solar. 
The thing about off grid is that the economics have greatly shifted in recent years. It used to be the case that solar panels cost a fortune, therefore you'd only have "just enough" and use big battery banks to cover periods of cloud. 
But in 2013 solar panels are ridiculously cheap so you can afford to install far more of them, thus generating significant power even on fully overcast days and bringing the batteries up to full charge whenever the sun comes out. The trend is thus toward much large panels and smaller batteries as a result. 
The basic "rule" with off-grid solar is to use electricity where you need it, and to use gas or wood for heating applications thus keeping electricity consumption down particularly during winter. So use solar + gas for hot water, gas for cooking, either gas or wood for heating. If you want a tumble dryer then yes, there are gas-powered ones (all fully legit and "off the shelf") which work just the same as electric. If you switch two thirds of your energy use to solar hot water, gas and wood then it's pretty easy to supply the remainder, that which you need to be actual electricity rather than just heat, from solar panels and batteries. 
Air-conditioning - yes you can run A/C from solar as long as the  solar system is properly sized to allow for it. You may need to run a  small generator to top up the batteries during an extended period of hot  weather but it can certainly be done. 
Generators - not as much hassle as you probably think. Easy way is just  get a small gas powered one (an "off the shelf" standard item) and  have it permanently connected to the gas (which will be from the same bottles for  everything that you have on gas in the house). That way there's no  messing about with petrol - if the batteries get low then you just start  the generator and leave it running for a while. 
I'm not obsessed with off-grid, I'm on the grid myself, but I'd quite happily use it if it were the cheaper option. As I said, it's good enough for the electricity industry itself to depend on solar to control some of the "real" power stations and it's good enough for safety signs in school zones. 
Personally, I'd get quote for: 
1. Grid connection by extending the HV line overhead + include the cost for usual electric appliances for hot water, cooking, heating. 
2. Off-grid with solar electricity, solar hot water with gas boost, gas cooking and either gas or wood heating. 
Both will require some ongoing maintenance on your part. Keeping trees well clear of overhead lines in the case of the grid. Keeping a check on the batteries (easy once you know how) and possibly using firewood for heating in the case of off-grid. Pros and cons to both. 
I'd get quotes before making a decision one way or the other.

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## paddyjoy

Thanks for all the advice, I have a few options now that I can investigate.

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