Advice needed on wiring for a log cabin

[Valizzo]

Hi guys,

Me and my partner have recently decided to build a log cabin at the back of her mum's house.
The electrician that the company's working with, is planning on using a 316 swa as the main power cable, but I have concerns as the cabin will be used as a permanent dwelling for a while and we'll have to fit an electric shower.

Now I'm thinking, we'd need something that should be able to handle at least 20 kw power draw to be on the safe side.

I'm not an electrician but based on my limited knowledge we'd need something rated for at least 90 amps.
Please note the cable will be buried and around 25 - 30 meters in length.

I'm out of my depth here so advice and a second opinion would be greatly appreciated.
Also, they quoted us £720 for the wire itself which seems a bit steep?

Thank you!

 

[Strima]

90 amps? What are you planning on growing in there?

Confirm with your electrician how he has worked out the maximum demand. If then your still not satisfied get further quotes from other electricians.

 

[ChrisElectrical88]

Whos digging the hole? Whats the earthing system in the house? I take it will have electric heating for the power you describe?

 

[Valizzo]

Whos digging the hole? Whats the earthing system in the house? I take it will have electric heatong for the power ypu describe?

They're doing the digging and everything. I'm not sure about the earthing system, the house was built in the 70s.
Yes we're planning on going with electric heaters as gas would stretch our budget considerably.

 

[davesparks]

Now I'm thinking, we'd need something that should be able to handle at least 20 kw power draw to be on the safe side.

I'm not an electrician but based on my limited knowledge we'd need something rated for at least 90 amps.
Please note the cable will be buried and around 25 - 30 meters in length.

If you need a supply that big then you'd better get in touch with the DNO and arrange to have a new connection brought in to feed this log cabin rather than try to run it from an existing supply.

How did you arrive at a demand of 20kW after diversity? Considering the average house will run quite happily on about 4kW that seems over the top!

 

[ChrisElectrical88]

£720 to dig 20m and install 16mm 3c SWA?

 

[Valizzo]

£720 to dig 20m and install 16mm 3c SWA?

No, that's just the price of the cable itself

 

[JAWS]

No, that's just the price of the cable itself

That Cant be right surely

 

[Valizzo]

If you need a supply that big then you'd better get in touch with the DNO and arrange to have a new connection brought in to feed this log cabin rather than try to run it from an existing supply.

How did you arrive at a demand of 20kW after diversity? Considering the average house will run quite happily on about 4kW that seems over the top!

I just roughly estimated the maximum demand with the heaters on during winter and shower running at full + appliances.
I'm not 100 % sure if that's how it works exactly that's why I'm asking if that particular cable would be adequate.
Thank you!

 

[ChrisElectrical88]

Cable should be about 250 at the absolute most. He might have included for rods in that orice and labout, wouldnt know without seeing the quote

 

[ChrisElectrical88]

I just roughly estimated the maximum demand with the heaters on during winter and shower running at full + appliances.
I'm not 100 % sure if that's how it works exactly that's why I'm asking if that particular cable would be adequate.
Thank you!

Tell the spark what you want and let him design it.

 

[Pete999]

No, that's just the price of the cable itself

"Taking the Proverbial I think.

 

[Valizzo]

Cable should be about 250 at the absolute most. He might have included for rods in that orice and labout, wouldnt know without seeing the quote

The labour is part of a different quote but the rods are most likely included in that.
All in all it amounts to £3850 for everything including labour / switches / sockets / fuse board etc
Was surprised as I expected the electrical work to cost less than the plumbing.

I did tell them exactly what I wanted and they did design it based on that.
It's very convenient for us to go with them, as they can take care of the plumbing and everything as well.
They assured me the 16 mm is adequate for what we need, I just wanted another professional opinion on the matter as time is of the essence, although I know details are very limited.
I really appreciate your help, thank you

 

[Valizzo]

"Taking the Proverbial I think.

It's not an assumption, it's what's on the actual quote.

 

[telectrix]

16mm is fine as regards current capacity, volt drop could be a factor though. your cable cost should be no more than £200.

 

[Andy78]

All in all it amounts to £3850 for everything including labour / switches / sockets / fuse board etc

I'll do it for £3.5k. I'll even chuck 25mm cable in to ease your mind

 

[ChrisElectrical88]

Trust their design, 16mm 63A submain its what i would imagine is going in.

 

[Valizzo]

I'll do it for £3.5k. I'll even chuck 25mm cable in to ease your mind

A most generous offer indeed!

 

[Valizzo]

Trust their design, 16mm 63A submain its what i would imagine is going in.

It's settled then, that's what I'll go with.
Thanks very much for your help Chris!

 

[ChrisElectrical88]

Just double check there not exporting PME in this situation and if bonding of the water submain is needed.

 

[Valizzo]

Just double check there not exporting PME in this situation and if bonding of the water submain is needed.

Just read about that thanks very much for the tip, I'll make sure to ask

 

[Midwest]

There's no trust in the world nowdays. Why not get several quotes, or just use a tradesperson recommended by word of mouth.

Not aimed directly @Valizzo, but this seems a common question being asked these days, on this forum. Not withstanding the forum is here to help, but one needs to do ones own groundwork sometimes (excuse the pun).

 

[Andy78]

There's no trust in the world nowdays. Why not get several quotes, or just use a tradesperson recommended by word of mouth.

Not aimed directly @Valizzo, but this seems a common question being asked these days, on this forum. Not withstanding the forum is here to help, but one needs to do ones own groundwork sometimes (excuse the pun).

I get the feeling this is an electrician provided by the cabin builders. I have had regular customers in this situation who have felt that they are unable to get quotes for part of the work as it is provided as a package.

 

[Strima]

I get the feeling this is an electrician provided by the cabin builders. I have had regular customers in this situation who have felt that they are unable to get quotes for part of the work as it is provided as a package.

My mother in law has recently had one built in her back garden, over £5k for power works. I've checked it over and the standard of work is crap. SWA not glanded, plastic conduit run externally but not correctly assembled allowing water ingress, the list goes on.

 

[davesparks]

Just double check there not exporting PME in this situation and if bonding of the water submain is needed.

With a 16mm 3 core SWA this shouldn't be a concern, the cpc is large enough bond any services

 

[Risteard]

16mm is fine as regards current capacity, volt drop could be a factor though. your cable cost should be no more than £200.

30 metres I would think nearer £260 to be fair.

 

[DefyG]

30 metres I would think nearer £260 to be fair.

Perhaps Telectrix is talking cost price with 1% margin? and/or excluding VAT!

 

[PhilGas]

No, that's just the price of the cable itself

As example, that cable from TLC Electrical Supplies would be around £150 for 20m!

 

[alasdairp]

No-one else has commented this, but just in case...
Permitted Development Rights usually allow small cabins up to 30 sq.metres and not more that 2.5 m high.

However, this is not the case if you want to have a residential log cabin which is going to function as sleeping accommodation or annex of your main house with water, drainage and electricity. If people will stay in it and it is not portable / moveable it will almost certainly (legally) need both Planning Permission and be inspected and tested to meet modern Building Regulations.

If it needs it and you don't get it, then if the LPA find out they may make you remove it completely.