Running power from block shed to metal shed - 1ft gap between gables

UKworkshop.co.uk

Help Support UKworkshop.co.uk:

Prizen

Established Member
Joined
19 Feb 2013
Messages
343
Reaction score
13
Location
Dublin
Hi all

i am building a metal shed behind my main shed and want to run power to it from my main shed.

i know burying SWA is the way to go, but I cannot do this. Would it be acceptable to run swa on the ground? Once the shed is built, the SWA wouldnt be accessible as it’s only a 1ft gap between gable of each shed.

also the consumer unit is at the opposite end of my main shed. Could I spur off one of the sockets on the gable end adjacent to my new shed?
 

RichardG

If at first you don’t succeed have a cup of tea.
Joined
29 Mar 2018
Messages
782
Reaction score
437
Location
South Norfolk
I can't answer about using SWA but a similar thing happened at work a few years back and the electrician ran a 1 inch galvanised conduit between the two buildings, probably about 1m distance at 2m height. He put a slight bend in the tube so the middle was lower than the buildings either side for water runoff. He continued the conduit inside to the distribution board and a new breaker. No SWA used.
 

RobinBHM

Established Member
Joined
17 Sep 2011
Messages
7,194
Reaction score
1,387
Location
Wst Sussex
I dont want to be a misery, but you do need to be careful regarding the earthing arrangements, especially as its a metal shed

A qualified electrician doing this would have to consider what the type of earth the house has and whether it can be exported to the shed, or whether the shed should have a TT earth. You also need to know what the CPC size should be

in general on running SWA externally, it is acceptable if its fixed to a permanent structure. IE you can run it above ground clipped to a house wall, or a garden brickwall. You couldnt fix it to a wooden fence.
 

TheTiddles

Established Member
Joined
14 Oct 2007
Messages
2,929
Reaction score
764
Location
Wiltshire
How much power do you need? Can you put in an extension cable between the gables and just it in?
 

John Brown

Social media influenza
Joined
25 Sep 2008
Messages
2,510
Reaction score
525
Location
Stinchcombe, Gloucestershire
I always though SWA had to be buried, but I spoke to an electrician who said it was fine to leave it on the surface, depending on where it is. He said the burial thing had come about owing to caravan sites and stake being knocked into the ground. He appears to know all the regs by heart, so I'm a bit confused now.
 

Fergie 307

Established Member
Joined
28 Dec 2019
Messages
1,118
Reaction score
547
Location
Sandy Bedfordshire
I would be a bit dubious about leaving it on the ground. Rats are drawn to anything new in their neighbourhood, and can chew through metal with surprising ease, including armoured cable. Usually a fatal mistake for the rat but still a PITA when you have to fix it. DAHIKT.
 

Sporky McGuffin

Light entertainer
Joined
22 May 2015
Messages
1,099
Reaction score
604
Location
Headley Down
I always though SWA had to be buried, but I spoke to an electrician who said it was fine to leave it on the surface, depending on where it is.

I believe it can be unburied, but must be secured to a solid structure (such as concrete fence posts).

That's how it was done for my last workshop (with a Part P certificate). For the current one it's run inside fibre reinforced conduit which is apparently very rat resistant.
 

guineafowl21

Established Member
Joined
28 Oct 2015
Messages
686
Reaction score
221
Location
Inverness
SWA is quite happy above ground - do a neat job and support it between the sheds, either with a taut wire, conduit or even a board. Drip loop is a good idea.

However, the metal of the building will need to be bonded to earth, typically by a 10mm2 conductor. It’s unlikely the SWA you’re planning to use will provide this, and nor will the socket you’re planning to spur from.

I recommend the usual ‘chat with a friendly electrician’. Anyone could wire up the the fittings and make them work, but if proper earthing isn’t considered, the job won’t be failsafe and you could be in a spot of bother in the event of a fault.
 
Last edited:

Jonm

Established Member
Joined
17 Jun 2020
Messages
704
Reaction score
336
Location
Warwickshire
I am not an electrician. My understanding is that if you are spurring off a ring main then one socket is acceptable. More than that needs to go through a fuse. Standard 13 amp fuse should be ok. I think there should be an isolating switch in the second building. SWA should have a core for earth, then the sheathing earthed separately. The glands on the SWA are fiddly and take time. I have no idea about earthing a metal shed but it seems like a good idea.

Whether you need a separate earth for the building I have no idea, it looks like a minefield. When the electrician installed the electrics to my garage, located about 20 metres from the house he did not install a separate earth. My mains garden lights, do not have separate earths. All installed as part of new build, certified, building regs and NHBC.

You should be using an electrician for this.
 

guineafowl21

Established Member
Joined
28 Oct 2015
Messages
686
Reaction score
221
Location
Inverness
Whether you need a separate earth for the building I have no idea,
If it’s the metal sectional shed that I’m thinking of, it’ll be considered an ‘extraneous conductive part’ and treated in much the same way as an incoming metal water or gas pipe, ie bonded with a big, fat earth.
 

Spectric

Established Member
Joined
19 Feb 2015
Messages
3,822
Reaction score
2,007
Location
North Cumbria
The obvious issue is the shed is metal, under the regs that is classed as an extraneous metal part and is your main issue if your house supply is a PME system, ie one in which the neutral is a shared earth. The reason is that if the neutral to your property became open circuit then power would still flow to all loads, then return down the Neutral to your point of supply and then to the Earth and you now could have an electrified shed and machinery beds in respect to ground. In such circumstances I would only run Live and neutral to the outbuildings and then install an earth pit and rod for the outbuildings so no metal components could have any potential above zero.

If the distance is only a foot then use a section of cable tray between the buildings which itself must be grounded. But as has been said this is not a DIY job and you need to consult an electrician, not just a domestic installer.

I am not an electrician. My understanding is that if you are spurring off a ring main then one socket is acceptable.
You cannot spur of a ring main and then run it outside of the main property, needs its's own circuit and protective device. Also ring mains are just legacy, I would never run a ring main in any new installation these days, well I have not for the last twenty years and would only advise radials.

SWA should have a core for earth
All depends on the design, as said if it is a PME system then just two core with armour earthed at the furthest point to the earth bar, itself grounded by a rod.

I always though SWA had to be buried

So long as it is secure then it can be burried, run on cable tray or clipped to a wall but never just suspended or run on a catenary.
 

Jonm

Established Member
Joined
17 Jun 2020
Messages
704
Reaction score
336
Location
Warwickshire
If it’s the metal sectional shed that I’m thinking of, it’ll be considered an ‘extraneous conductive part’ and treated in much the same way as an incoming metal water or gas pipe, ie bonded with a big, fat earth.
I was referring to a separate earthing rod(s) for the building, irrespective of whether it is metal or not. It seems to be a minefield of conflicting advice.
 

Jonm

Established Member
Joined
17 Jun 2020
Messages
704
Reaction score
336
Location
Warwickshire
You cannot spur of a ring main and then run it outside of the main property, needs its's own circuit and protective device.
Interesting, are you saying that if you have an outside socket spurred off the ring main that you cannot change the socket for an external FCU (13 amp) and run a cable from it to a shed?
 

guineafowl21

Established Member
Joined
28 Oct 2015
Messages
686
Reaction score
221
Location
Inverness
I was referring to a separate earthing rod(s) for the building, irrespective of whether it is metal or not. It seems to be a minefield of conflicting advice.
Yes, that’s the earthing system for the building, which is separate, but related to, the bonding of metalwork.

I think the minefield is a result of different systems calling for different solutions. This video:


... is an interesting discussion of what’s involved. He does cover exporting the common TNCS earth, but in many cases it would be safer to TT (earth rod) the building in its own right. Again, a walk round with a friendly electrician will cover all that.
 

Spectric

Established Member
Joined
19 Feb 2015
Messages
3,822
Reaction score
2,007
Location
North Cumbria
Interesting, are you saying that if you have an outside socket spurred off the ring main that you cannot change the socket for an external FCU (13 amp) and run a cable from it to a shed?
It all depends upon distance, what loads you expect to supply and what the current ring main parameters are. If it is for a socket and light as many builders provide so they can say there is power in the garage then it may be ok but if we are talking about a workshop with it's own distribution board then no, this is a different ballgame but in all these situations it involves design / change from original design and so an electrician should be used.

Also current regulations do not need to be retrofitted to existing installations, yes that is always a source of debate because if what has been done is Ok then why is it not Ok under new guidance.
 

HamsterJam

Established Member
Joined
10 Jun 2018
Messages
385
Reaction score
176
Location
Warwickshire UK
And don’t forget all outdoor electrical work should be Part P signed off either by a competent person (aka qualified electrician) or the council building control.
 
Top