Outdoor Electrics

Jas12 · 17 Sep 2005

We are in the process of building a summer house in the garden and would like to add some power, probably a double socket and some lighting. I have a spare 10A MCB on my consumer unit in the house, my initial thoughts were to run a 2.5mm cable from this to the garage (garage integral with house) then in the garage install a DP RCD (63A 30mA trip ?) then from there run 3 core 2.5mm armoured cable outside. The first part of this outside run would be underground approx 15m then another 15m overground tacked to the bottom gravel board of a wooden fence to the summerhouse.

My questions are -

1. Is the overall setup ok?
2. Would I need to upgrade the MCB in the main consumer unit to 16A, 32A or more?
3. When installing electrics outside how deep underground do I have to go, are there any special rules, is it ok to run the cable along the bottom of the fence?
4. Would there be a limit to the number of sockets and/or lights I could add in the summer house.
4. Can anyone suggest a better alternative solution?

Thanks J

breezer · 17 Sep 2005

try a search on power to shed, power to garage its been done before

Steve · 17 Sep 2005

A few quick observations.

10A is fine for a couple of lights etc, but if you're wanting a small heater out there, best make it 16 / 20A, which i believe 2.5mm² SWA can carry safely.

Tacking to gravel boards is frowned upon, since they are not considered "permenant". Underground the whole distance would be better. Also, use the right cleats and screw, not tack.

Best to leave out the RCD in the garage and fit a Garage consumer unit in the summer house (2-way mini CU with RCD and 6A and 16A MCBs already fitted)

No limit to how many sockets you can have, since if you use appliances totaling over 16A, the MCB in the garage CU will trip before the cable melts.

Lectrician · 17 Sep 2005

20amp mcb at origin (on rcd side of cu if you have a split type).

SWA underground to summerhouse, with 2.5mm between sockets in summerhouse. Include a sw/fuse spur for the lights, used as a light switch if only one light switch required. Use an unswitched fused spur if you require 2way or or multiple ganged switching.

If CU is not a split type, install preferably a 30mA/20amp RCBO, or fit an RCD somewhere between the CU and the summerhouse.

ban-all-sheds · 17 Sep 2005

crafty1289 said:
10A is fine for a couple of lights etc, but if you're wanting a small heater out there, best make it 16 / 20A, which i believe 2.5mm² SWA can carry safely.

Safely, yes, but volt drop would be too great over 30m. 4mm² would be the minimum, with the usual caveats of 6/10mm² "just in case" if there's a lot of digging involved.

Best to leave out the RCD in the garage and fit a Garage consumer unit in the summer house (2-way mini CU with RCD and 6A and 16A MCBs already fitted)

Jas12 - is the spare way already RCD protected?

I take the opposite view to Lectrician - the cable itself doesn't need RCD protection, and it's better, IMO, to have the RCD nearer the point of use, so that you don't trip the house circuits out if something happens outside and you don't have to trudge back to the house to reset it, and conversely if you're in the house you don't have to go outside to sort out whatever it was that caused the trip before you can get the house working again.

Jas12 said:
When installing electrics outside how deep underground do I have to go

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

Lectrician · 17 Sep 2005

I too normally take that stance BAS, but with a small summerhouse, and a budget, can't see a problem.

A seperate RCD Would be ideal, just another cost.

Andy Fenn · 18 Sep 2005

HI there,

Should he connect the SWA at the exsisting and new consumer unit or to make connections easier, would it be more practable to connect the SWA to a junction box then use T & E to connect to any of the consumer units?

ban-all-sheds · 18 Sep 2005

Definitely the latter - terminating SWA in a CU, particularly a plastic one, is awkward if it's already stuffed full of other cables. But you need a metal adaptable box, not an ordinary JB.

If the layout permits you can fit the box touching the CU, and then simply leave the SWA cores very long and take just them into the CU, thus avoiding the use of connector blocks.

Even if they won't go next to each other you can do the same thing by using conduit to connect the box and the CU.

Jas12 · 20 Sep 2005

OK thats been a great help guys,

Thanks a lot, J

Andy Fenn · 20 Sep 2005

Sorry about this ban-all-sheds but would you please expand on the metal adaptable junction box theory.

Firstly, I totally agree with you, if poss, keep SWA connections out of CU.

However, not sure I understand you totally, getting a little confused with your metal box and keeping the SWA cores long.

If you kept the SWA cores long, would you be able to do away with the metal box, me just being thick and not being sble to visualise things.

Would 2.5mm SWA suffice for a 22m run to power one light and 3 double skts?

Many thanks.

breezer · 20 Sep 2005

i think ban all sheds is saying how are you going to be phsically able to terminate a swa gland inside a domestic cu, using a metal box you would not have to

ban-all-sheds · 21 Sep 2005

Andy Fenn said:
Sorry about this ban-all-sheds but would you please expand on the metal adaptable junction box theory.

Firstly, I totally agree with you, if poss, keep SWA connections out of CU.

However, not sure I understand you totally, getting a little confused with your metal box and keeping the SWA cores long.

Rough sketch:

If you kept the SWA cores long, would you be able to do away with the metal box, me just being thick and not being sble to visualise things.

SWA needs to be properly terminated in a gland like this:

- you can't do it in mid air.

Remove locknut 3.
Strip cable outer sheath and pass shroud then outer nut 1 over cable.

Pass cable end through gland inner 2 and spread out armour wire over cone.

Screw outer nut 1 onto inner 2 and tighten.

Insert gland bush 4 into cable entry of apparatus and tighten locknut. Push shroud back over gland.

See //www.diynot.com/forums/viewtopic.php?t=27081 for one man's trials, with photos.

Would 2.5mm SWA suffice for a 22m run to power one light and 3 double skts?

Go here: http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html , select 2-core PVC SWA (even though you should use 3-core) and work it out.

However, given that you need to dig a 15m trench about 70cm deep (see http://www.tlc-direct.co.uk/Book/7.13.3.htm), you would be well advised to consider if you'd ever want to do that again, and to install 10mm² SWA so that if you ever decide to, e.g. put a sauna out there, you'll have the capacity.

I take it you are aware of the requirements of Part P of the Building Regulations regarding this work?

Andy Fenn · 21 Sep 2005

ban-all-sheds, you are a star, many thanks for all the info, as well as all you other leckies.

Just a couple more questions- this particular design will prob not be practical for the job I have in mind so I was thinking along your earlier view of connecting the SWA to T & E in a metal junction box. Would 2.5mm be ok bearing in mind we are dealing with one light and 4 double sockets which are not going to be used for anything inparticular.

Secondly, an electrician has told me that he was picked up by the NICEIC for not installing an EARTH SPIKE for a supply to a shed and it's in the regs but he can't remember where abouts, ANY idea's please.

Many thanks.

ban-all-sheds · 22 Sep 2005

Andy Fenn said:
Just a couple more questions- this particular design will prob not be practical for the job I have in mind so I was thinking along your earlier view of connecting the SWA to T & E in a metal junction box. Would 2.5mm be ok bearing in mind we are dealing with one light and 4 double sockets which are not going to be used for anything inparticular.

Yes, that would be OK - MCB no bigger than 20A. Do consider what I said about oversizing the SWA though - look at the overall cost difference for the whole project between the 4mm² you need for the distance involved and 6/10mm², and think about the difficulty of digging the trench and if you'd ever want to do it a second time.

Secondly, an electrician has told me that he was picked up by the NICEIC for not installing an EARTH SPIKE for a supply to a shed and it's in the regs but he can't remember where abouts, ANY idea's please.

This was probably in connection with exporting a PME earth. Not sure if there is anything in the regs about it, but GN5 does discuss it, and you can see the relevant pages here:

http://supplychain.org.uk/phpBB2/viewtopic.php?t=41

Also there is an article in the IEE Wiring Matters magazine issue 16, (which isn't on-line yet) - very briefly summarised here:

http://www.screwfix.com/talk/thread.jspa?threadID=23124&tstart=0

Andy Fenn · 22 Sep 2005

Ban, point taken regarding the oversizing of the SWA for future designs.

Going back to your brill diagram showing how to use a metal adaptable box next to a cu to make an SWA connection.

I would really prefer to take my SWA connections in both the new metal shed CU and the house plastic CU.

However, unlike your diagram, my house CU is on one side of a wall and on the other side I would like to try to fix your metal box, prepare the SWA then pass it through the normal size garage wall into the house CU, thus having no junction boxes and making the connection directly within the house CU.

Can't really put the metal box next to or near the house CU as it is in a utility room and not sure this would look tidy.

Your views please.

diynot

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Outdoor Electrics

breezer

breezer

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