Armoured cable

[DougR]

I have to put in a mains cable to my new house across fields. I have the farmers permission to do dig a trench and the soil is light and sandy. I am aware that I have to think of the voltage drop, the distance is 350 meters. I am assuming that I have to use armoured cable but what size of cable should I use, can I put in a telephone cable in the same trench? Any ideas as to cost of cable and where I could get it?

Anything I need to be aware of

 

[bongos]

Alot of things to be aware of.

Firstly have you spoken to your DNO to ask about a separate supply for your new house? It may cost a bit but I think it would be better to do this than run SWA 350m.

If you have a prosed load of say 100A for your house (are you heating your house with gas or electricity?) then you will need a very large cable to run for that length.

Not to mention EFLI values on an install that long.

Speak to the DNO about your own dedicated supply.

 

[bhm1712]

where are you planning to supply the new house from?

The DNO will charge alot, but it will be done properly. The size of cable and length required for this is likely to cost thousands, at a length of 350 meters, a 3 core 10mm sq SWA cable is going to cost you around £3000. Thats just 10mm sq, not the size you will need.
I dont imagine that the DNO will charge less than £10,000 to do this job, if there really is no supply closer to your new house.

this is not a DIY job really.

 

[flameport]

Due to the length, even a modest load of 50A would require cable of 95mm or larger.
Such a cable will cost thousands of pounds. You won't be able to install it yourself either, since the cable itself will weigh in excess of 1 tonne.

 

[jeepmadmike]

It's going to be expensive! Think I'll stick this one into amtec software and see what size it thinks up! I'm going to guess a 4c 50mm with the cores doubled up might pull it off but the source charateristics will be an issue.
No problem having the phone cable in the trench with it and I would want it atleast 2ft deep if it's fields it crosses.

As for installing it, have your wetabix that morning! It will be easy if you hire a drum stand, the route dead steight, and the trench accessible all the way with a vehicle

this job would be worth getting a specalist to price up for the supply install and connect

you could get all Eco and fit loads of PV cell and a wind generator and a big battery bank but that's going to cost more money!

 

[mfarrow]

at a length of 350 meters, a 3 core 10mm sq SWA cable is going to cost you around £3000.

Over £8 per metre? Time to find a new cable supplier!

It's all correct though, you'd need something pretty large and expensive to go that distance. If you insist on doing it DIY though consider the following:

A parallel cable run will make the cables more manageable for installation.

A step-up and step-down transformer arrangement will reduce your cable size drastically. Consider about 800V.

Is the farm fed by split-phase? If so you can halve your cable size straight away.

 

[DougR]

Thanks to all who replied. Here is a bit further info.

We have been quoted £8500 by hydro board to fit and connect cable that is with us paying for the trench to be dug ourselves. This is from the nearest supply we can connect to. I feel that this is expensive however they will not break this figure down. They say a connection fee if the cable is onsite near to the house will only be a few hundred pounds.

Nay futher info will be useful to us.

 

[Adam_151]

If you are laying a cable for the DNO to connect into their street main and provide you a cutout on the end of, then that changes things somewhat

The DNO will have to be happy with the cable, have they sent you a specification and chances are it probably won't be SWA, more likely concentric if SPN, or waveform if TPN

You need to go back to the DNO with your requirements (I feel that over that distance it'll probably be better to go for say 45Kva across three phases (60A per phase) rather than 25Kva on a single phase (100A SP)), and ask them what cable they require (and if they can arrange supply of it) for you to install (again as per their spec - can't remember what the spec is under farmed land, but going to be deepish)

 

[ColJack]

705.522 says at least 1m under arable or cultivated land

 

[mfarrow]

I would say they're probably not screwing you over at that price for a 350m length. The copper alone will cost them at least half that. Then they've got to lay it, project manage the installation, do the connection, pay the meter installers, etc...

I know of a 3p 180kVA city centre supply costing £120k, so that you're lucky stars you haven't got that!

 

[bongos]

We have been quoted £8500 by hydro board to fit and connect cable that is with us paying for the trench to be dug ourselves. This is from the nearest supply we can connect to. I feel that this is expensive however they will not break this figure down. They say a connection fee if the cable is onsite near to the house will only be a few hundred pounds.

Is this for 3ph/split phase/single phase?

Unfortunately it doesn't sound like it will be much cheaper due to the cable length. If you go with their quote will this mean they are installing the main incomer on your property and they become responsible for the cable? Although you shouldn't have any problems once it's laid, if it becomes your responsibility then if there was a problem it could become a very expensive fix for you.

Also bear in mind that the DNO's can (and will) be very picky about your trench digging etc. It would be wise to find out exactly what they want you to do in terms of preparation and get it all in writing from them to confirm it too.

 

[ColJack]

no chance of 11KV overheads along the field boundries and a pole transformer at your end?