What SWA cable

[rs6mra1]

I have the opportunity to buy armoured etc cable at a reduced price (wholesaleers + discount) but i need to know what size would be ideal.

I have just had a garden office built and initial power supply would be for the lights and about 6 double sockets and a lamp post in the garden.

When the house was renovated a few years ago the electrician (cannot get hold of him now) ran a 10mm twin and earth cable from the fuse box at one end of the house to the back of the house (not connected of course) total length approx 25 metres. This was done in anticipation of me needing power outside.

The garden office is located 15metres from where this cable now ends.

I plan on building a workshop early next year which would be 45m from where the cable ends now or 30m from where the garden office is.

Bearing in mind what i need to have done soon to the office and also what is planned for next year, what size SWA would be ideal and also what suggestions as to other items have you for me to take advantage of reduced prices?

Please note that the workshop would be running the normal power tools and the most power hungry tool would probably be a table saw but nothing fancy.

Thanks.

 

[ban-all-sheds]

Your starter pack of the info you need is here:

• 
  
  
  
• //www.diynot.com/wiki/Electrics:books
  
  
• //www.diynot.com/wiki/Electrics:MCBtoCable
  
  
• http://www.tlc-direct.co.uk/Book/4.3.1.htm (all subsections)
  
  
• http://www.tlc-direct.co.uk/Book/4.3.11.htm
  
  
• http://web.archive.org/web/20070327014113/http://www.kevinboone.com/cableselection_web.pdf
  
  
• http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html <- Specify 2-core cable and PVC, even if that is not what you are using or it will make invalid assumptions.
  
  
• http://www.tlc-direct.co.uk/Book/5.3.1.htm
  
  
• //www.diynot.com/wiki/Electrics:MCB2
  
  
• http://www.tlc-direct.co.uk/Book/7.13.3.htm
  
  
• http://www.tlc-direct.co.uk/Book/8.1.1.htm
  
  
• //www.diynot.com/wiki/Electrics:SWA_gland
  
  
• http://electrical.theiet.org/wiring-matters/16/elect-inst-outdoors.cfm?type=pdf
  
  
• //www.diynot.com/wiki/Electrics:Part-P
  
  The references above which are in italics are out of date. The principles are still valid, and you can absolutely learn valid things from them, but you will need to refer to the latest edition of the Wiring Regulations to get the correct data. Also, apologies, the web.archive link isn't working - still to be resolved.

If you want to assume the role of designer, then it has to be you who actually does it, not some random strangers on the Internet. For a start, those strangers won't be able to sign this:

I being the person responsible for the design of the electrical installation (as indicated by my signature below), particulars of which are described above, having exercised reasonable skill and care when carrying out the design hereby CERTIFY that the said work for which I have been responsible is to the best of my knowledge and belief in accordance with BS 7671:2008, amended to 2011 except for the departures, if any, detailed as follows:

It will have to be you, and you'll need to be justified in signing it, so you'll need to acquire sufficient competence so that you know what you are doing.

Also, be aware that if the workshop will require Building Regulations approval then you will need to show how you'll comply with Part P even if the electrical work would not have been notifiable in its own right.

 

[dhutch]

Will you be fitting the cable yourself? If not I would speak to whoever you have in mind to fit it.

Else to me and someone whos done the job with careful advice from here and a working knowledge if not specific training, it would make sense to continue the run in 10mm^2 SWA for the remaining 15m, but exactly what they can the run from that and what you could connect it to within the house would depend on a lot of things, including the route of the existing cable (thermal dissipation and if its suitably protected to not require rcd protection).

I am sure others will be along in time.

 

[rs6mra1]

I inadvertently deleted the first reply but hell knows what the guy was going on about.

Dhutch: Thanks for chipping in but i can confirm that I have no intention of doing any of the work as I am aware that there are regulations in place to which i am not familiar and will not even have the time to look into.

To be clear, in the absence of my finding a suitable electrician i just wanted to know what materials i can purchase whilst i have the chance in hand. Had I been able to get hold of the guy that did some work for me previously I would not be posting this just in case someone else like the other guy comes along with the complete works of Shakespare.

 

[bernardgreen]

10mm² might cost a bit more but having a cable too large is not a problem ( electrically ) and allow for extra loads later.

One thing to be careful about is the table saw, if the motor is larger than 1 Kw then you need to have a chat with the DNO as to whether the supply to you property is able to cope with the starting current of the motor.

//www.diynot.com/forums/viewtopic.php?p=3236764#3236764

 

[rs6mra1]

10mm² might cost a bit more but having a cable too large is not a problem ( electrically ) and allow for extra loads later.

One thing to be careful about is the table saw, if the motor is larger than 1 Kw then you need to have a chat with the DNO as to whether the supply to you property is able to cope with the starting current of the motor.


Noted re the table saw and thanks for your input.

 

[securespark]

If you have a good discount on the cable, considering the 40m run (is your house really 25m deep???) and the fact you have 10 milli already installed (sure it's 10 mm²?), I would, as others have already said, continue the run in 10 milli.

You have voltage drop for starters, plus the supply cable will be ready for future expansion.

Make it 3 core as well.

Then leave the rest to a spark. You may want, with his direction, to dig a trench for the cable, to save money.

 

[dhutch]

I presume the 25m run is far from line of site, but even then, it does seem long.

Presumably also well rules out running SWA all the way back to the incoming supply, distribution board and or consumer unit.


Daniel

 

[rs6mra1]

I have just measured it again and its about 19m from the very front of the house where the distribution board is to the back. I recall the electrician saying he used about 25m as he had to go up to the first floor and then carried on into the loft in the part of the house all the way to the back where the cable has been sat doing sweet nothing.

so i am set on buying 10 mm² SWA in 3 core. I just had another thought as to what might as a RCD might be required. Is it easy to determine that at this stage or am i better off leaving that to whoever does the job?