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SWA Wiring to shed from existing outdoor socket
Stillfirm
2 Posts
Question
hi people, I’m new to the forum, and seeking a bit of advice. My shed (well it’s more of a small open fronted barn/fire pit area) is about 20 metres from the house. Requirement is to run a couple of sockets (or two pairs) and a couple of lights.
I have a length of 3core SWA cable and some existing outdoor sockets on the side of the house.
my thinking is to put the SWA straight in to the existing double socket, run it down the garden (digging in) and in to a junction box to supply the sockets.  The lighting could also be plugged in to the sockets if it made it simpler.
only likely to be running the odd power tool, radio, lamps or other such stuff, fairly light use.
Does this sound ok?
14 Replies
mapj1
2886 Posts
More info needed. 
1) how are the existing sockets supplied - own circuit, or spurred off the house ring, or just hung off the back of the light switch  ? You need to know, and to be sure they are in fact supplied correctly to begin with, i.e. from a circuit that can take the load, and the supply cable is co-ordinated with the rating of the fuse or breaker, and there is RCD protection.
If they are spurred off an existing ring, it is a very good idea  to add a fused spur or RCD spur with a switch inside the house to protect just the outdoor bit, than you can isolate it when you go on hols or if water gets in.

2) This SWA - what is it's copper cross section? - for sockets over that distance I'd expect at least 2.5mmsq if the circuit fuse or breaker was 20A or less. Perhaps 4mmsq. Again, the cable size needs to co-ordinate for the rating of rest of the circuit. Look up how to terminate the IP rated glands unless you already know what you are doing.
3)Digging in  - if it is not under a concrete path, I'd suggest aim for half meter down or more, in case the garden gets dug at some point.

4) Earthing. How is your house earth, TT, TNS or TNC-s . Also is the shed floor timber and dry, or cement or earth or possibly damp, and is it possible you may plug something in and take it outside ?
Please confirm all these things, as it affects what is recommended for the earthing at the shed end of thing

5) Using a fused spur off the power cct.  for the light switch at the shed end may be OK - but you do need to think about what happens if lights all trip off due to a faulty appliance  - emergency lights or any critical loads.

So in summary it may well be OK, but it depends.





 
Zoomup
1882 Posts
I have just undertaken a consumer unit renewal. The house was previously owned by a builder. The new owners are having lots of work done including a new kitchen. The builder had run an S.W.A. cable from the back of a downstairs' room socket through the wall to a pond pump position. The cable did not have the armour earthed, well it was not even connected. The outdoor socket was an ordinary indoor type on a pattress mounted on a low wooden stake. No R.C.D. protection at all. The circuit was protected by a B.S. 3036 30 Amp fuse.  The socket was protected from the elements by a removable wooded "hat" that wobbled a bit on the socket stake. Needless to say I disconnected the cable.

Z.
Chris Pearson
2068 Posts

Zoomup:
The cable did not have the armour earthed, well it was not even connected.

I must say that it is not at all obvious to a lay person that the armour should be earthed; it seems reasonable for a lay person to assume that the purpose of the armour, as with other forms of armour, is to provide mechanical protection.
Zoomup
1882 Posts
Yes, that is exactly it Chris. That is why unqualified people should not dabble in the sacred art of electrical engineering. They should leave it to us, the professionals, don't you think?

Z.
Chris Pearson
2068 Posts
Judging by the horrors under my daughter's floorboards electricians should not dabble in the sacred art of electrical engineering. 😯

The interesting thing is that virtually all, if not all, of the defects have been revealed on inspection rather than testing.
Zoomup
1882 Posts
Exactly, you (experienced electrical engineer person) know what to look for in the electrical dept. whilst playing with the spiders under the floor boards. 

Z.
Stillfirm
2 Posts
Thanks guys, back to the more info required qs - I’ll come back with some more info. I fitted SWA previously for some outdoor sockets onto appropriate junction provided by my electrical contractor - and earthed it 😀👍
mapj1
2886 Posts
Good. You pretty much always should connect  the armour to the earth at the supply end, for all the common house earthing arrangements.
However the earth at the load end may or may not be taken from the armour, it may instead be that the armour is insulated, and earth taken from a local electrode, depending if it is better to create a TT island for the load - examples where it is better to have a local earth rod and not use the suppliers earth at  the load end, when the suppliers earth is PME /TNC-s include for car charging points, swimming pools, areas with earth floors and livestock, caravan pitches, and a few other situations. Examples where you would use the house earth are if it has a dry wooden floor and all the electrical items are domestic, and essentially indoors.
Between those extremes lies a large  area requiring some thought.
inserv
3 Posts
hello ,
the best way to have this done is to make he connection straight from your distribution board the the SWA  if there was space in there and  if there was a lay the cable on the outside wall. Then  protect it with 16 or 32Amp MCB depending on what loads you want in the shed.
.
Connecting the SWA in to the existing socket is not the best practice as you might over load that particular socket
drE
2 Posts
I kind of have the opposite scenario to Stillfirm - I have a radial running out to the garage and am wondering if I can put an outside socket on the existing line. Situation is as follows:
  1. Radial from main consumer unit wired with 4mm2 (earth is also 4mm2) to outdoor junction box at rear of house (This is where I would like a new outdoor socket)
  2. 3-core 4mm2 SWA from junction box to garage at rear of garden. SWA is earthed at house end.
  3. Junction box on outside of garage 4mm2 takes carriers into garage consumer unit.
  4. Sockets and lighting from garage consumer unit as normal.
What I would like to know is whether I can replace the Junction Box at the house with an outdoor socket and simply have that socket inline with the rest of the installation (points 2 and 3 above). The installation was done by a professional, but as I'm looking to add a single socket I'm wondering if this is doable by myself without running into tricky issues in relation to regs. My thinking is that even though the proposed socket would be before the consumer unit in the garage, it would still effectively receive protection from the breaker and RCD in the main CU in the house. Is this sensible thinking or am I missing something here?

Part of the reason I'm looking at doing it myself is to minimise exposure to the outside world in the current climate.

Does anyone have any thoughts? Thanks
mapj1
2886 Posts
Again, probably OK, but you do not say what the breaker and RCB at the house end are, or how the building is earthed, or the earthing of the armoured cable at the garage end for that matter - if you cut into the cable that feeds the garage, you need to do things in way that deos not accidentally leave it 'off earth'. Please think very hard also about the weather proofing, and minimise the number of cable joints outside and places water can get into
As above, if the socket is for charging an electric car or a caravan hook up, other rules apply.
I'm not trying to put you off, but as so often with apparetlyuy simple questions, 'more info needed' I'm afraid.
I'm also assuming you can make off the SWA glands properly - as a note try the John Ward tutorials on-line if a bit rusty, and you posses a meter and the ability to check earth continuity polarity etc.
Mike.
ebee
930 Posts
Zoomup:
I have just undertaken a consumer unit renewal. The house was previously owned by a builder. The new owners are having lots of work done including a new kitchen. The builder had run an S.W.A. cable from the back of a downstairs' room socket through the wall to a pond pump position. The cable did not have the armour earthed, well it was not even connected. The outdoor socket was an ordinary indoor type on a pattress mounted on a low wooden stake. No R.C.D. protection at all. The circuit was protected by a B.S. 3036 30 Amp fuse.  The socket was protected from the elements by a removable wooded "hat" that wobbled a bit on the socket stake. Needless to say I disconnected the cable.

Z.

Sounds like one of the better jobs that builders tend to do Zoom 😉

drE
2 Posts
Ah aye, sorry, was typing in a rush and tried to tick all the important bits off in my head - obviously missed a few points while others were a bit ambiguously implied. So if it helps answer further:
  • Earthing of house is TN-S.
  • Breaker for the garage is 32A.
  • RCD is 63A/30mA.
  • The SWA is only earthed at the house end. The garage earth is through a 4mm2 carrier within the SWA, back to the earth of the house.
  • The SWA does not run all the way back to the CU of the house. It only goes as far as the junction box that I want to replace with a socket.
The idea would be that there should be no cutting through of the SWA or existing cabling. As there is already a JB in the position I want the extra socket the idea would be to get an IP66 socket and have the radial from the house come into that (including the earth) and then attach the SWA into a gland entry on the socket to continue the radial to the garage. Hopefully that makes more sense. Thanks for the input, it's very much appreciated.
mapj1
2886 Posts
Yes, a 4mm radial in SWA is likely to be fine on 32A MCB and 30mA RCD. Just make sure you allow yourself enough room to get  all the cables in, if need be add an new  deep box with blank cover along side or a junction box on the the indoors side where it is T and E.
With TN-S  you do not need to worry, just export the house earth as-is.
Of course  some of TNS properties are now on a mix of TNS-TNC-s on the same substation, and you may not know, but that only changes when new properties are added or significant repairs to the network on an estate of existing houses the risk of sudden change are quite low.
Mike.

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