Cable Size to Log Cabin Studio

[wcavanagh]

I have just ordered a large log cabin for the garden....

It will be used as a Photographic Studio.

I know it will need SWA from the main CU to a smaller CU in the cabin.

My question is on calculating the size of this SWA.

3,8Kw Heater / Air Con
1.4Kw Coffee Machine
150W Fridge
Studio Flash lights are rated at 300W each, but for under a second X 4 of these.
4 Strip lights for standard lighting
1 Computer

I will want a ring main round the studio with plenty of sockets, so I can plug the studio flashing in any location without causing trip hazard.

The cabin is 40m from the house. The house has a TNS supply with 80A Main Fuse.

 

[Taylortwocities]

Are you planning to do this work yourself, or use a registered electrician?

 

[wcavanagh]

No, and No.

Im trying to get an idea, I have had two quotes and both have different ideas of cable size.

Quote 1 - 10mm SWA 3 Core
Quote 2 - 16mm SWA 3 Core

And about £300 difference in price.

 

[Taylortwocities]

The answers are a choice of

Yes and no
or
No and yes

If you are not doing it yourself you must use a registered electrician.
He/she will be able to self certify the work and complete the building regulations paperwork. this is a legal requirement.

40metres is a fair way for a sub main. You have to consider the volt drop for the circuit, otherwise your coffee will never get hot.

The difference in price between 50 metres of 10mm² and 16mm² three core SWA is about £70, so that won't account for your £300 difference.

 

[wcavanagh]

The only difference I can work out from both quotes is the size of the SWA.

Same number of sockets, same lighting, altho one installed a "Plastic JB" to exterior of house, and termination into that.

Why would one spark calc 16 and calc 10

I dont know enough about it, but surely they would use same formula.

One also mentions earth rod, and 2 core SWA. Maybe that is the £300.

 

[ban-all-sheds]

No, and No.

So you're not DIYing and you're not using a registered electrician?

10mm² probably OK, 16mm² I'm sure would be - what's the distance between your incoming supply and the cabin?

But the difference in price between 10mm² and 16mm² SWA is nowhere near £300....

 

[wcavanagh]

Doh, like I say I have had 2 quotes from local sparks, they are doing the work, and as the building is over 30m square Building regs are involved for checking everything.

I have seen the difference now, one is 2 core and other is 3 core.

The distance from the main CU and Cut Out is 40m give or take 500mm.

Does it make a difference that one spark wants to use 2 core and earth rod, and the other wants 3 core and no earth rod?

I want to pick the best quote, not just on price but quality, as a business will be run from this studio.

Cheers for all your help so far.

 

[Weavertronix]

Personally I would use 3 core SWA because it will have a lower EFLI which would be better for the computer.
Some electricians just convert systems to TT for every outbuilding, which isn't necessary unless you need main bonding.

 

[ColJack]

The answers are a choice of

Yes and no
or
No and yes

If you are not doing it yourself you must use a registered electrician.

I object to this statement..

you do not have to use a registered sparky at all and saying you do is a flat out lie to get more work for the registered sparkies..
unregistered sparkies are perfectly capable of doing the work but will have to notify the LABC and pay the fees as a DIYer would ( or maybe a discounted rate if the LABC allows ) or could do the work if it's already been notified as part of the overall work ( would a log cabin require notification for other things? ).

He/she will be able to self certify the work and complete the building regulations paperwork. this is a legal requirement.

as I said above the non-registered sparky is also capable doing this but might require testing and inspections from the LABC..

 

[Taylortwocities]

Yes, ColJack. Perhaps I was being a little harsh with that.

In one of the quotes the electrician is to provide an earth electrode at the cabin. The other seems to be exporting the earth from the house.

I guess both quotes include a separate RCD consumer unit in the cabin itself?

There are a number of things to consider for an installation like this. For instance, is there a water pipe or other extraneous conductive part in the cabin? This may require additional work.

There is a (now out of date) article on some of the considerations
here

 

[ban-all-sheds]

I've never seen the sense in discarding a perfectly good TN earth unless you really have no alternative.