Electricity supply to garden sheds seems very unsafe

Discussion in 'Electricians' Talk' started by HaveAGoButNoHero, Dec 17, 2013.

  1. Hi. I have bought a tip of a house – affordable – and have loads of repairs to do on it. This is one example of the electrics that I know needs some work! Please can you comment and advise me on what I’ll need to do/buy, safety and legal aspects etc?
    There are two garden sheds, where lighting and sockets are supplied via a spur that starts behind a socket situated in the spare room. The socket powers my computer etc, nothing else. The fuse in the main consumer unit (a modern one!) that “protects” this circuit is a MK LN5916 B16. Is this sufficient?
    The cable (twin core and earth, sheathed, 2.5mm² i THINK) exits tha house wall, then goes underground for 2 metres to first shed, where it feeds into an old (?cartridge?) 30A fuse (photos). Then on into a wall-mounted double socket (photo). This is where the real fun begins, I think. This double socket supplies, via plugs 1). the fluorescent light in this shed and 2). the next shed, 4 metres away. This second shed is larger, the cable runs underground to it, up the outside in plastic tubing(pic), and in to a fuseboard (pic) containing a 40A, 30mA RCD and a MK B6 and MK B16 circuit breakers. From here, supply splits to feed 3 fluorescent lamps and 3 double socket outlets, plus two exterior spotlamps.
    I’m sure that the feed to the second shed needs to done in a way that does not involve a plug, please can you comment? Both sheds are quite damp.
    I don’t have a clue if the cable is enclosed in any armour, I don’t intend on digging anywhere near until I do.
    Any advice will be most gratefully received. Many thanks.

    Attached Files:

    Last edited: Dec 17, 2013
  2. Coloumb

    Coloumb Well-Known Member

    Hi mate, not sure if I would say it's "unsafe" as there don't appear to be any live exposed parts. The design doesn't really work very though.

    It looks like the whole thing is fed of single 16a mcb to switch fuse and fuses that have a higher rating but I can't see clearly in the pictures. This is a fairly pointless exercise since the 16a mcb will blow first in a fault or overload.
    It's the same with the 2nd cu fed off the 13a plug. The plug will go first unless it the ctt fed off the 6a mcb. Also, technically anything fed from a plug does not count as "fixed wiring" and does not come under BS7671.
    What's a bit more concerning is that there is no 30ma rcd protection in the first shed, which is not really good at all.

    The general level of workmanship is pretty poor as I would have used singles in placky conduit throughout but that's a personal preference.

    Also, if the cable is run in placy conduit and buried a couple of feet down then you don't need to use swa. There should be marker tape where it's been run though.
    Finally the earthing will need to be addressed as you don't say what you have (TT-TNS-PME) and if you need any bonding done.

    Anyway, I'm not a spark so prolly one of the guys can add some value.
  3. stateit

    stateit Well-Known Member

    Rough, but not necessarily an immeadiate danger to life and limb.

    The twin & earth into a 13A plug must have been a right sweary one for the previous owner to do, and is not recommended.

    Your best 'quick fix' would be to add 2 x fused connection units ('fused spurs') adjacent to the double socket in shed 1.

    From one of these, fuse at 13A, and run the 2.5mm T&E for Shed 2 from this.
    From the other, fuse at 3A, and run the T&E to the lights.

    That'll make things better while you can think about getting someone in / mugging up yourself, on how to do it 'properly'.

    The consumer units in the sheds are by-the-by as the ultimate protection is the 13A fuse in the spur in the house. Hopefully that is supplied via an RCD.

  4. Thank you for getting this started Coloumb. I since discovered a junction box hidden behind cans on a shelf, have attached pic. This is situated in the first shed, a little way after the plug that beginds the stretch to the second shed. The cable (1.5 mm or 2.5 mm twin core and earth) is then joined to an armoured one, which is something positive, I think, but it doesn't look to have large diameter copper either though, and the brown and black colours suggest "old", don't they?

    I don't understand the earthing issue you refer to, i.e. TT-TNS-PME), or bonding, so I'll have to do some research.

    Can anyone give me a basic breakdown of what the ideal set-up would be please, materials required etc. but keeping any of what currently exists wherever possible?
  5. Great, many thanks, I will do this. I just want it as safe as possible for now, then will have go at doing a proper job soon.
  6. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Looks like the 'brown and black' in the armour are new, but should be live and earth, grey being neutral!

    Unless I'm mistaken!

    Mr. HandyAndy - Really
  7. Coloumb

    Coloumb Well-Known Member

    If you google wiring matters external wiring there is an article by the IEE (4th down). Tbh mate if you don't know the basics about earthing then your prolly not going to understand what's invloved. BUT ultimately to comply with BS7671 you will need to issue an EIC which you won't be able to do without test gear. Also part p will come into play. Sorry to **** on your chips but it is what it is.
  8. Oops! But if neutral is linked to earth at present, how is it that there is power to shed 2 ? Same mistake at the shed presumably.
  9. Sean_ork

    Sean_ork Screwfix Select

    there's many millions of homes with similar ''installations'' such as your's, and you'll not see reports of folks being electrocuted in droves, so don't be overly worried - I assume you will have had some form of condition report with your survey ?

    perhaps when the dust has settled get a few electricians to give the house a once over with a view to doing whatever is required, try and educate yourself as to what is typical so you don't get mugged into having unnecessary works done - just don't be tempted to heat the sheds with a few 3Kw heaters
  10. Sean_ork

    Sean_ork Screwfix Select

    don't worry too much about that - it's just slightly unconventional and is missing some identification sleeving
  11. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Same mistake probably. Not dangerous if both matching!

    But could be confused.

    Mr. HandyAndy - Really
  12. Okay gents, it is quickly becoming clear that I am well out of my depth here! I was hoping it would be a simple fix. I want it safe a.s.a.p. so will call in a professional. I did have a survey done, but in all honesty I think that the Homebuyer Surveys here in Scotland are a waste of money - they satisfy the lender but don't provide a true or thorough picture to the buyer. Many thanks for your comments.
  13. Sean_ork

    Sean_ork Screwfix Select

    you do tend to get what you pay for ;)
  14. Yes, that's true to an extent, but even a "thorough" survey doesn't result in carpets and floorboards being lifted - if he had, he would have uncovered a hell of a mess - floorboards demolished so that electric cables could be replaced, but then any old crappy piece of wood being simply laid on top to fill the hole and the carpet stapled down on top - the surveyor noted "creaky boards, normal wear and tear"; the underside of these boards were burnt where there had been an electrical fire at junction boxes, and so on! The list is a long one here, it's amazing the lengths people go to to hide faults.
  15. Sean_ork

    Sean_ork Screwfix Select

    those pesky Scots ...
  16. Bloomin foreigners! They were English like me!
  17. Walter System

    Walter System Member

    The three core inc earth, armoured cable that is used to extend a supply to a shed. Does the outer metal armoured layer need to be earthed even with an RCD at the house end and the earth core connected to the earth bar at CU in the house?

    This link given is very good:

    But it was written in 2005 before the 17th regs. It also does not mention if an armoured cable needs its outer metal earthed.
    Last edited: Dec 21, 2013
  18. seneca

    seneca Screwfix Select

    Yes it does, preferably at the supply end, even with an rcd. The reason being that if the cable became damaged it's just possible that the live could connect with the armour and if that isn't connected to earth anywhere the rcd wouldn't trip but but the armour could come up to mains potential!
  19. Walter System

    Walter System Member

    Thanks. Can it be connected at the shed end, the earth core and the outer metal part of the cable? Probably via an earth bar in a shed CU?
  20. seneca

    seneca Screwfix Select

    You can connect it both ends which will improve your Zs a bit but it is important to connect the supply end as that's where the danger will be if the cable is damaged. The supply end of the cable could remain live, unlikely with an rcd in circuit but worth being aware of.

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