SWA cable to garage 8m

[Mattsell76]

I have a 4mm2 SWA cable already but not installed.

The run to the garage going up the wall outside the house to the consumer and to the consumer in the garage is about 8m

At the moment I have 2 lights and 4 2 gang sockets in the garage.

I used to use it with 4mm2 cable. To power lawn mover, edge trimmer and some power tools, along with a tumble drier. Obviously not all at the same time. Usually 2-3 of these on at a time (Dryer, Lawn mover and drill)

1. In the future I would like to put a fridge and freezer in there too. Will 4mm2 be enough or should I go for 6mm2 or higher?

2. Can I bring the cable through the floor of the garage?

3. Is it worth investing in conduit and what would be suitable if I could get from screwfix, B&Q or wickes?

Thank you for you time.

 

[ban-all-sheds]

1. In the future I would like to put a fridge and freezer in there too.

How cold does it get out there in the winter?

Will 4mm2 be enough or should I go for 6mm2 or higher?

• //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/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.
  

2. Can I bring the cable through the floor of the garage?

Only you know that.

3. Is it worth investing in conduit and what would be suitable if I could get from screwfix, B&Q or wickes?

Not needed for armoured cable.

http://www.tlc-direct.co.uk/Book/7.13.3.htm


Also, don't forget this: http://www.tlc-direct.co.uk/Book/8.1.1.htm and that a new circuit is notifiable, and requires you to get Building Regulations approval before you start.

 

[plugwash]

SWA doesn't need protection when run underground. If you want to be able to replace the cable in future then run it in ducting.

If I was doing it in my own property then while I had the trench dug i'd also run a duct for data/telecoms/alarm/cctv cables. Note that you aren't supposed to run mains and ELV signal cables in the same duct unless the ELV cables are insulated to mains voltages and finding mains rated communications cables isn't easy.

4mm SWA will be fine for a 32A circuit at the distances you mention and a 32A circuit will be fine for the loads you propose.

 

[ericmark]

Also, don't forget this: http://www.tlc-direct.co.uk/Book/8.1.1.htm and that a new circuit is notifiable, and requires you to get Building Regulations approval before you start.

This guy is in Wales so needs to notify anyway still on old Part P rules.

The supply to sockets or other items where load can alter has to rely on the size of the MCB to protect the cable and in the main even a 13A fuse will normally hold on a garage supply as rare we will use over 3kW at same time.

Clearly if the washing machine was on water heat cycle and you start lawn mower at same time it may over load but that is rare. We have a caravan on a 13A supply together with outside stuff like lawn mower and fuse has never blown.

4mm SWA is likely rated over 32A and that's a fair current. However as BAS has pointed out you need to measure things like the loop impedance and calculate volt drop there is no magic formula it needs some maths.

Often electricians will estimate and take a chance when complete it will pass the limits but this is when we are doing it every day and some times we do get it wrong and have to swap the cable for a heavier one after we have tested.

To be frank once you want over a 13A supply it's not really a DIY job. The cost of hiring meters before and after and LABC charges mean just not worth the effort.

 

[ban-all-sheds]

This guy is in Wales so needs to notify anyway still on old Part P rules.

Which make new circuits notifiable.

 

[Mattsell76]

Interesting replies. Thanks.

When I bought the house (2006) it had 4mm2 cable in plastic pipe going from the house to the garage along the top of a high wall, this would have been fitted at some point by the previous owner (house is 1960's so would not have had power originally to garage). The wall has since been taken down as it was unstable and moved to a new place, hence the SWA cable idea to re-power the garage. I was wondering if I needed to pay for the building regs (how much is that?) if it was already there so to speak?

Getting the cable through the floor of the garage will probably be the best option to me and looks do-able. So happy with that.

So to clarify also, you think: 4mm2 will be ok to run a fridge, a freezer, a tumble dryer, and maybe the lawn mover and edge trimmer at the same time? I would only every likely to have the 3 white goods on at the same time and one other tool or garden equipment. Trying to think how close to the cable ratings these would be.

Can you point me in the direction of the calculations please?

 

[JohnW2]

When I bought the house (2006) it had 4mm2 cable in plastic pipe going from the house to the garage along the top of a high wall, this would have been fitted at some point by the previous owner (house is 1960's so would not have had power originally to garage). The wall has since been taken down as it was unstable and moved to a new place, hence the SWA cable idea to re-power the garage. I was wondering if I needed to pay for the building regs (how much is that?) if it was already there so to speak?

You may unfortunately be the victim of 'national politics'. Under current rules in England, if you were merely replacing an existing cable (and hence not creating a 'new circuit') the work would not be notifiable. However, Wales is still working to the 'old' (England+Wales) rules, which, unless you could argue that you were 'replacing a damaged' cable, and that it did not form part of an 'outdoor installation', would mean that the work was notifiable. If that is the case, and since notification is likely to cost 'a few hundred pounds' (typically £200-£400) it would probably make more sense to employ a self-certifying electrician to do it.

Kind Regards, John

 

[Mattsell76]

Thanks for that John

Anyone help with getting the ducting? Screwfix, B&Q, Wickes or would I need a specialist Electric Shop?

 

[ban-all-sheds]

Can you point me in the direction of the calculations please?

That pointing took place in the first reply:

• //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/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.
  

 

[Mattsell76]

Cheers. Looked at the voltage drop calculator and not sure off what to select as there was not buried in ground option.

Just done a measure to the garage and it 10m-11m up and down the walls to the consumer unit. Will this effect the cable size much?

In the garage the wiring starts at a mini consumer unit and is only spurred off with 2.5mm2 and separate 1.5mm2 for lights all through plastic conduit. Will the 2.5mm2 need to be in a mains loop for the white goods I might need in the future? - fridge, freezer, tumble dryer, with one or two garden tools on at max on top would be biggest load.

 

[Iggifer]

If you choose SWA 2 Core it will only give you two options for reference method (application) Clipped Direct or Underground, clearly you want underground.

You can run ~38a on a 4mm SWA underground, dependant on how it travels through the house - what cables it's joined to inside etc etc

 

[JohnW2]

Cheers. Looked at the voltage drop calculator and not sure off what to select as there was not buried in ground option.

Voltage drop will not be affected by burying - try one of the other options.

Kind Regards, John

 

[Mattsell76]

It seems everyone is saying 4mm2 is fine for the job which is great news.

If I'm placing through ducting. How do I get the cable through the 90 degree bends at either end? With the initial cable I guess I could place that through the ducting and then position the two in place.

Or if in the future it needs changing does the ducting just have a straight run either end and you dig to this and feed new cable as and when in 30 years its required?

 

[Iggifer]

the best way to do it is to try and avoid 90 degree bends. slow sweeping bends, where you can are easier to pull cable in

Also, when you pull in your existing cable, pull in a number of lengths of string, this will allow you to replace it in the future if needs be (of course you can just pull the old cable out from the garage with a piece of string or the new cable attached to the other end but the string idea is much easier)

 

[Mattsell76]

the best way to do it is to try and avoid 90 degree bends. slow sweeping bends, where you can are easier to pull cable in.

I was assuming that but was thinking of the has to be at 500mm depth. So was thinking sweeping bends would result in me digging even deeper. I'm thinking the SWA cable will not be as easy to thread through the eye of the needle so to speak.