Electric to log cabin

[diycooper]

I am looking at getting electric put in log cabin, In my loft I have a 10mm T & E cable isolated which runs to the fuse board on a 40amp fuse. I was thinking of connecting 2.5mm SWA cable to the T & E in the loft then running it down my house and burying underground to the shed. In the shed connect it to a garage consumer unit with 2 fuses. 1 32 amp fuse for a ring sockets and 1 6amp for a light. What my question is 2.5mm SWA cable sufficient ?

I know 4mm would be better but taken diversity into account is the light going to make a massive difference ?

Thanks

 

[Taylortwocities]

If the fuse on that 10mm is 40amp then you can not connect 2.5mm cable to it.
The fuse would have to be reduced to 20 amp at the most.

Cannot say if 2.5mm will be sufficiant. What is the distance to the shed? That is key.

Also, what is your supply type?

 

[diycooper]

Why you say 20 amps was thinking 32 amp for main fuse ?

I gathered it was 20 amp for a 2.5 radial and 32 amp for a 2.5 ring circuit.

Cable distance is 18 meters tops.

Supply is 240v.

Thanks for reply

 

[Lectrician]

2.5mm SWA is not rated for 32amps.

When you say you know 4mm will be better, what do you base this on? 6mm would be better too, and 10mm, 16mm, 25mm, 35mm, 50mm.

Do you believe your 32amp MCB in the shed would descriminat against th 32amp MCB in the consumer unit?

For 18m, would it really cost you that much to up the cable size to one which will allow a decent sized supply?

If your loading is light, why not just fit a 20amp MCB, 2.5mm SWA, and then just stick a couple sockets in the shed, directly from the SWA, with an FCU for the light? Make sure it is RCD protected in the house CU.

 

[diycooper]

2.5mm SWA is not rated for 32amps.

When you say you know 4mm will be better, what do you base this on? 6mm would be better too, and 10mm, 16mm, 25mm, 35mm, 50mm.

Do you believe your 32amp MCB in the shed would descriminat against th 32amp MCB in the consumer unit?

For 18m, would it really cost you that much to up the cable size to one which will allow a decent sized supply?

If your loading is light, why not just fit a 20amp MCB, 2.5mm SWA, and then just stick a couple sockets in the shed, directly from the SWA, with an FCU for the light? Make sure it is RCD protected in the house CU.

I base 4mm being better than 2.5 on the basis that its ovious you can up the cable size but do I really need to.

Cable price is nearly double hence why I ask.

I was thinking of doing it that way but would it be any different to fit a garage consumer unit with a 20 amp for sockets and then take a FCU off for light or even still why not just use the 6 amp spare fuse in the garage consumer unit for the light. This way if it trips it will be in the cabin.

 

[diycooper]

Just thinking I will do it that way. If I change the fuse in the MCB to 20 amp this then runs to the to the loft in 10mm T & E, this is what I want to use as to run another cable from MCB is nightmare as where the consumer box is. What is the best way to connect the 2. SWA to 10mm T & E ?

Thanks for replys

 

[Iggifer]

not sure where you're getting your cable prices from!

Screwfix:
25m of 2.5mm 3-core £41.59
25m of 4.0mm 3-core £55.80

Not really nearly double the price

http://www.screwfix.com/c/electrical-lighting/armoured-cable/cat830462

 

[diycooper]

Was using Toolsation and Ebay for 4mm as Toolsation did not sell 4mm.

http://www.ebay.co.uk/itm/4MM-3-COR...al_Components_Supplies_ET&hash=item3cc0b623eb

http://www.toolstation.com/shop/Electrical/Cable/d190/sd2730

But thanks I will go with the 4mm SWA.

 

[ericmark]

2.5mm SWA cable to the T & E in the loft then running it down my house and burying underground to the shed.

Without going further twin and earth is not suitable for burying.
And the regulations state:-
433.2.1 Except where Regulation 433.2.2 or 433.3 applies, a device for protection against overload shall be installed at the point where a reduction occurs in the value of the current-carrying capacity of the conductors of the
installation.
NOTE: A reduction in current-carrying capacity may be due to a change in cross-sectional area, method of installation, type of cable or conductor, or in environmental conditions.

So 10mm SWA would seem more likely to meet the requirements.

However it does not stop there the next question is earthing method. This with depend on location and outbuilding construction.

There is a very good reason why in a domestic premises Part P requires one to notify any work done outside. There are so many problems in selecting what is required. Even electricians from time to time make errors. My neighbour has got an electric van. The electrician installing the charging point has used the TN-C-S (PME) supply but that is not allowed. Has to be TN-S or TT. I am sure when the paperwork is submitted to his scheme provider they will pick up on this and send him back.

Point is there is a huge difference between it working and being safe.

 

[diycooper]

I understand just 1 point though I was not implying I was going to bury T & E if I read right. I ment bury the SWA then lead up the wall into loft then connect to the t & E in loft.

 

[Lectrician]

And the regulations state:-
433.2.1 Except where Regulation 433.2.2 or 433.3 applies, a device for protection against overload shall be installed at the point where a reduction occurs in the value of the current-carrying capacity of the conductors of the
installation.
NOTE: A reduction in current-carrying capacity may be due to a change in cross-sectional area, method of installation, type of cable or conductor, or in environmental conditions.

So 10mm SWA would seem more likely to meet the requirements.

Umm....

There is nothing wrong with using the 10mm T+E jointed to a new piece of 4mm or larger SWA on a 32amp MCB - This is what regulation 433.3.1 (i) permits.

"A device for protection against overload need not be provided for a conductor situated on the load side of the point where a reduction occurs in the value of current carrying capacity, where the conductor is effectively protected against overload by a protective device installed on the supply side of that point"

 

[diycooper]

And the regulations state:-
433.2.1 Except where Regulation 433.2.2 or 433.3 applies, a device for protection against overload shall be installed at the point where a reduction occurs in the value of the current-carrying capacity of the conductors of the
installation.
NOTE: A reduction in current-carrying capacity may be due to a change in cross-sectional area, method of installation, type of cable or conductor, or in environmental conditions.

So 10mm SWA would seem more likely to meet the requirements.

Umm....

There is nothing wrong with using the 10mm T+E jointed to a new piece of 4mm or larger SWA on a 32amp MCB - This is what regulation 433.3.1 (i) permits.

"A device for protection against overload need not be provided for a conductor situated on the load side of the point where a reduction occurs in the value of current carrying capacity, where the conductor is effectively protected against overload by a protective device installed on the supply side of that point"

So I am fine to do it this way. What is the best way to connect SWA to t & E . A adaptable box ?

 

[EFLImpudence]

//www.diynot.com/wiki/electrics:installation_techniques:swa_gland

 

[diycooper]

Thanks and considering its a radial circuit I am doing change the MCB fuse to a 20 amp ?

 

[ban-all-sheds]

cooper - please at least be honest with yourself, if not us.

Do you really think that you are capable, genuinely capable, of carrying out electrical design work?

And if you're not, do you really think that you should try to muddle through on the back of asking questions here as and when you happen to realise there's something you don't know?

You've shown, by the questions you've asked and the mistaken assumptions you had been working to, that you really don't know enough to be attempting to do this design.

The project you plan to do may not be "rocket science", but I can assure you that it involves knowing far more than you think it does.

There's nothing wrong with asking questions here - they can be a useful part of a learning process, but they are not a substitute for proper structured studying. The key term there is "learning process" - you cannot learn all the things you need to know just by asking questions here. It isn't structured enough - it won't provide you with a way to progress where each step builds on what you learned before.

You can't carry out a job of this magnitude by asking whatever random questions happen to occur to you. You've already shown that you have some dodgy misconceptions - what if you get something wrong because you have no idea your knowledge is wrong? What if you miss something because you simply have no idea it even exists, and just don't realise you don't know it?

• //www.diynot.com/wiki/electrics
  
  
• //www.diynot.com/wiki/electrics:books
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/electricity.html
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/domesticinstallations.html
  
  
• http://www.tlc-direct.co.uk/Book/1.1.htm[/list]I strongly suggest you get stuck into the last link right away - it won't give you design ideas, and unfortunately it doesn't refer to the current edition of the Wiring Regulations, but it's free, and will still give you a good grounding which you can augment with more up to date publications. And it might help you realise the scope of what you need to learn.