Cable size ?

[Ashley2001]

Hi

I'm wanting to run a new 32amp supply to an outhouse 43metres from consumer unit and having done armoured before hope to do myself but I am unsure of the size of armoured cable which will be part clipped and buried

It will be supplying a board with 1x16amp for sockets 1x16 for a heater and 1x 6amp circuit for five spot lights 50watt each all rcd protected from the consumer unit

Any help with the size of cable required would be much appreciated and my logic so far

 

[ban-all-sheds]

• //www.diynot.com/wiki/electrics:mcbtocable
  
  
• http://www.tlc-direct.co.uk/Book/4.3.1.htm
  
  
• http://www.tlc-direct.co.uk/Book/4.3.11.htm
  
  
• http://www.tlc-direct.co.uk/Book/5.3.1.htm
  
  
• http://web.archive.org/web/20080213151445/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.
  

 

[jamesmcbride]

You would be better off having the rcd in the outhouse, rather than the house consumer unit.

 

[Ashley2001]

You would be better off having the rcd in the outhouse, rather than the house consumer unit.

Thanks I understand but would it be better at mains to protect armoured where it is not buried

I know this can be a pain if the rcd was to trip in outhouse but protecting the cable and anyone from it is that not better ??? Any help with cable size ??

 

[Monkeh]

You would be better off having the rcd in the outhouse, rather than the house consumer unit.

Thanks I understand but would it be better at mains to protect armoured where it is not buried

I know this can be a pain if the rcd was to trip in outhouse but protecting the cable and anyone from it is that not better ???

It's armoured cable. Not only would they have to be really, really trying, but the stuff is designed to open a fuse or MCB when something metal penetrates it.

Any help with cable size ??

Much as I hate to support BAS, the relevant information has already been posted. Please read.

 

[Lectrician]

The SWA does not need RCD protection to comply with the regs. I would put the RCD the shed end personally.

On that distance, and at 32amp, you would be looking at 10mm 3 core as a minimum.

 

[Ashley2001]

Ok many thanks for that

Can anyone help with cable size ?

 

[Lectrician]

I thought I did....

 

[Ashley2001]

To reduce cost if I was to reduce to a 20 amp circuit would a 6mm cable be sufficient if I only fitted one 16 amp circuit for sockets and one 6 amp for lights

Just trying to get all alternatives

 

[Ashley2001]

You did sorry I did not see your quote

 

[Lectrician]

If you went down to 20amp, 6mm would be OK. I would probably then just run the 6mm to the first socket (metal clad), and then run 4mm to other sockets and the heater switched FCU, and a switched FCU for the light. Put the RCD protection in the house. Simpler.

 

[Ashley2001]

If you went down to 20amp, 6mm would be OK. I would probably then just run the 6mm to the first socket (metal clad), and then run 4mm to other sockets and the heater switched FCU, and a switched FCU for the light. Put the RCD protection in the house. Simpler.

Many thanks for that ... I'm thinking ill run 6mm to a rcd protected garage fuse board with 1 x16 and 1x 6 mcbs and do away with heater on a 20 amp circuit as not wanting to use m/c sockets as it looks more like a room .. Many many thanks for your help

 

[Lectrician]

You could take the SWA into a 35mm deep flush backbox with flush socket if you prefer a 'room' look, or if surface, a white PVC back box (not moulded). you could even change from 6mm SWA to 4mm T+E via a moulded IP rated enclosure such as a gewiss type box, and this could even be placed at the rear of the shed, outside, if you wanted.

A 20amp MCB feeding a submain to a CU is odd TBH - The 16amp MCB will not descriminate with the 20amp (although may well not against the 32 either).

It would be far simpler to run a simple radial circuit rather than introducing a CU.

 

[Taylortwocities]

The cost difference between 6mm and 10mm SWA 3 core is only about £1 a metre. I would put in the 10mm and future proof the installation.
Much easier than digging it all up again in 5 years if you need some more watts in the future.

 

[Ashley2001]

Ok thanks makes sense for future watts ... So think we all agreed then if I go for original quote at beginning 10 mm2 is a sufficient size to run 43 metres ?