SWA to T&E

[N0vice]

Hi,

First post so excuse any major errors in judgement.

I am looking to run 6mm swa from a dedicated 32a RCBO in the house to a small shed consumer unit. Don't worry I won't be hooking anything up, just digging the trench, running the cable etc.

The run is 25 m from the back of the house, 35m to CU. I will be running an A rated freezer, bench tools (lathe, pillar drill, not all at once) and the odd garden tool but pretty sure the wife will have other, more accurate ideas, hence the 6mm. Depth of trench will be 600mm (sand and tape etc) with a separate earth at the shed.

There is 2.5mm T&E cable going to an existing external socket already on this 32a RCBO.

I'm positive I don't have enough space for 6mm SWA under the floor in the house so my question is (before anyone corrects me on the above), can I run new 6mm T&E to this external socket and junction this of to the socket / shed respectively, or should I try to keep this as a single run?

As I said qualified sparky will be hooking it up and testing, I'm just doing the ground / non skilled work.

Any advice you can offer would be appreciated.

P.s The wife wants another freezer running in the shed for Christmas (25m away). I was going to run a 1.5mm extension from the external socket (RCBO) for 2 weeks absolute max to the shed (be gentle ). Freezer will be the only thing running.

 

[JohnW2]

There is 2.5mm T&E cable going to an existing external socket already on this 32a RCBO.

Is that cable only supplying that one socket? If not, it's certainly non-compliant with regs - and some may not even be happy with it if it is only supplying the one socket.

I'm positive I don't have enough space for 6mm SWA under the floor in the house ...

I'm not sure I understand that, or its significance.

.... so my question is (before anyone corrects me on the above), can I run new 6mm T&E to this external socket and junction this of to the socket / shed respectively, or should I try to keep this as a single run?

I'm not certain I understand this, either - are you proposing to replace the present 2.5mm² T&E to the socket with 6mm² SWA, and then take the rest of the SWA from there to your shed? If so, that should be acceptable.

However, as I'm sure others will tell you, you really need to discuss all this with your electrician, since (s)he may not be happy to 'hook it up and test it' if (s)he hasn't been involved with, and agreed to, all stages of the design and construction process.

Kind Regards, John

 

[N0vice]

Hi John,

Thanks for the response.

Yes the 2.5 is supplying the single socket, I know it's 2.5 as I opened it to have a look. As for whether it's acceptable I would submit to your better judgement? I've not engaged an electrician yet as this is all theoretical at the moment. The problem I have is that there is very little space available in the conduit space (running through dining room, kitchen and bath room) to easily run cable out to the external wall (diameter wise) so swa may be too thick to do so.

I am wondering if I (or my electrician) can run twin and earth to a more convenient junction inside the house, then from that junction to the shed in swa?

Essentially I'm trying to find out if the floor has to come up.

Thanks

 

[OwainDIYer]

You can put a junction box on the outside of the house, take SWA from the ground into the base of the box, and take T&E through the back of the box and straight through the house wall.

 

[N0vice]

Just a note, I understand there is a design process, I am not going to start doing anything until I've spoken to a certified electrician. Just want to get an idea of the extent of damage.

 

[JohnW2]

Hi John, Thanks for the response. Yes the 2.5 is supplying the single socket, I know it's 2.5 as I opened it to have a look. As for whether it's acceptable I would submit to your better judgement?

Having 2.5mm cable supplying one socket is not, per se, a problem - the potential issue is having it protected by a 32A MCB. Provided the cable is not too long, I would probably be happy - but others may disagree!

...The problem I have is that there is very little space available in the conduit space (running through dining room, kitchen and bath room) to easily run cable out to the external wall (diameter wise) so swa may be too thick to do so. ... I am wondering if I (or my electrician) can run twin and earth to a more convenient junction inside the house, then from that junction to the shed in swa?

There is no reason why the indoor bits have to be SWA - so, if it would help,it would be perfectly acceptable to have the initial (indoor) part of the run in 6mm² (or maybe 4mm²) T&E, before changing to SWA at some box (or accessory) - as I said, maybe making the join at the present socket. As I said, I'm sure your electrician will have views on what approach should be taken.

Kind Regards, John

 

[JohnW2]

You can put a junction box on the outside of the house, take SWA from the ground into the base of the box, and take T&E through the back of the box and straight through the house wall.

As I've suggested, he probably wouldn't need a JB for that - he could probably use the existing outdoor socket.

Kind Regards, John

 

[N0vice]

Thanks John / Owain,

The worry was running cable = lifting floor so that's a load off.

As you say I'll speak to the electrician regarding the actual plan, this is all academic at the moment and I'm jumping the gun.

The run to the socket is less than 10m, I might be mistaken on the rating of the RCBO? It was an existing installation, would you recomend getting I checked out?

Thanks again

 

[ban-all-sheds]

A few points.

As JW2 said, the outside socket might be a good place to join the cables, and you must discuss any work you do with your electrician before you do it. She might want to see the trench before it's backfilled, or might be happy with photos showing the depth, the bedding etc.

You might want to consider putting ducting in, so that more or replacement cables can be pulled in later if necessary. Two ducts can be useful, as then you can also run phone and data cables out there - they don't cost much, and you never know.

Twin-walled ducting like this is the stuff to use:

http://www.drainageonline.co.uk/Ducting/Black-Twinwall-Duct-x-50m-coil.htm

Also, considering the marginal difference in cost, why not put in 10mm² to give you more contingency?

As for supplying it, I think it's better to use a switchfuse direct from the meter at the house end, rather than a CU circuit, particularly if that circuit would be RCD protected.

And a couple of questions:

1) Why do you want a separate earth at the outbuilding?

2) Are you aware of the problems of putting freezers in unheated outbuildings, like they don't work when it gets cold?

 

[N0vice]

Now data cable I know! Great idea on the ducting. As for the switch fuse I'll discuss with the electrician. Which ever solution is best / safest. Based on past experience my requirements are usually trumped by my wife's.

She'll want tumble dryers and all sorts no doubt? Plan for the worst and all that...

 

[ban-all-sheds]

Tumble driers are easy to prevent.

Don't pave the space between house and shed - she'll not want to tramp through mud carrying clean washing.

 

[N0vice]

Ha ha ha! Brilliant!

 

[DIYTom]

2) Are you aware of the problems of putting freezers in unheated outbuildings, like they don't work when it gets cold?

You can get freezers designed for unheated out buildings. We have a big chest one in our garage. It's a John Lewis own brand. Check on the label that it specifically says that and you'll be fine.

http://www.johnlewis.com/john-lewis...r-a-energy-rating-106cm-wide-white/p230588082

 

[JohnW2]

You can get freezers designed for unheated out buildings.

You can, but you have to look quite carefully for them - the vast majority of domestic freezers and fridges come with a warning that they are not suitable for use in unheated outhouses.

Kind Regards, John

 

[flameport]

You can get freezers designed for unheated out buildings. We have a big chest one in our garage. It's a John Lewis own brand. Check on the label that it specifically says that and you'll be fine.
http://www.johnlewis.com/john-lewis...r-a-energy-rating-106cm-wide-white/p230588082

Such things might be available, but that freezer is not one of them.

Minimum Ambient Operating Temperature 10°C