Garage Feed Armoured Cable Size

Discussion in 'Electrics UK' started by mr2paul, 8 Jun 2005.

  1. mr2paul

    Joined:
    8 Jun 2005
    Messages:
    5
    Thanks Received:
    0
    Location:
    Derbyshire
    Country:
    United Kingdom
    Having an extension done now and need to put an armoured cable feed to garage now before floors concreted

    I have two spare 6mm twin and earth cables routed from the consumer unit (but not connetced to supply) sitting in ceiling space ready to be connected to anything. Put these in before wall was all plastered and decorated

    I intend to use one of these to connect internally to a 6mm armoured cable run into garage ( about 3M away from house)

    QUESTIONS ARE...

    a) Can I use both 6mm twin and earths connected together to join onto a armoured cable larger than 6mm, say 10mm, to cope with possibly higher loads (thinking of future garden sockets, lights, possible hot tub one distant day)

    b)Presumably there is no point connecting a single 6mm twin and earth from the consumer unit a armoured cable greater than 6mm, i.e connect the 6mm T&E from consumer to a 10mm armoured cable to feed garage

    c)Once the electric is fed to gargage, intending to feed any other external elecric requirements out from garage, i.e garden lights. However want to be able to switch lights garden lights on off from inside. Presuming I will need an additional 3 core SWA fed in for each switched outdoor lighting circuit. Is 2.5mm ok for this lighting circuit switching for a max distance of 20m

    Really appreciate any advise help on above questions and need to resolve soon as theyre wanting to concrete extension flloor

    Paul
     
  2. plugwash

    Joined:
    28 Mar 2004
    Messages:
    8,818
    Thanks Received:
    265
    Country:
    United Kingdom
    iirc this is actually allowed provided the cables follow the same route.


    over such a short run no. Once you get to runs where volt drop becomes significant this can change though.

    i'd generally advise use of 3 core SWA with a core used for earth. the price difference is pretty small and it gives a much more robust earth path (especially if the glands are poor quality or badly made off). remember however even if you use a core for earth you MUST earth the armour


    1.5mm will be fine for this. if you wan't two way switching though i'd advise 4 core though so that you have a core for earth.
     
  3. mr2paul

    Joined:
    8 Jun 2005
    Messages:
    5
    Thanks Received:
    0
    Location:
    Derbyshire
    Country:
    United Kingdom
    Brilliant..much appreciated.

    So plan is to use BOTH 6mm T&E cables run together from same MCB already available at house consumer unit to connect to one 10mm 3 core SWA to run underground and supply garage CU 5m away

    This supply to garage CU should then be sufficient for requirements now and in future to run from the garage :p (garage sockets and lighting, outdoor sockets and lighting circuits, greenhouse heater ..one day maybe spa bath and who knows whatelse)

    Will also run two 4 core 1.5mm cables through to enable two garden lighting circuits to be switched internally. plus potential for two way switching.

    What and excellent resource this is, many thanks.
    Paul
     
  4. ban-all-sheds

    Joined:
    27 Aug 2003
    Messages:
    52,052
    Thanks Received:
    2,033
    Location:
    London
    Country:
    United Kingdom
    When did you apply for, and get, Building Regs approval for the extension? Just wondering if Part P will apply to the electrics, in which case you should be talking to Mr Inspector about the way that they handle non-registered or DIY electrical work.

    Why? What I mean is what made you choose two 6mm² cables and plaster them in before you really know what you'd be doing with them?


    Yes, you can - provided the 2 cables are the same length, same size, same construction and same installation method, so that they have the same capacity and share the load equally. They must be dedicated to this load, i.e. no branch circuits on either of them.

    Not if you want to exploit the capacity of the SWA from day 1, but then one 6mm² T/E cable has less capacity than the 6mm² SWA anyway. However, if you're thinking about future proofing, it'd (presumably) be easier to replace the internal cable linking to the CU than to dig up the garage floor to replace the SWA, so from that POV it might make sense to put in 10mm² and only use a 6mm² connection to it. As long as the MCB is rated for the 6mm² T/E it'll be perfectly safe.

    That will be fine. Frankly, for a 6A lighting circuit 1.5mm² would be OK.

    If Part P applies you should speak to LABC asap - it's more than likely that they, or the person they appoint, will want to see the depth and the run of the cable before it is concreted over. Also, although it's very unlikely to be faulty, it would be such a p*sser to have to replace it that I'd advise a continuity and insulation resistance check of the cable before the pour...
     
  5. mr2paul

    Joined:
    8 Jun 2005
    Messages:
    5
    Thanks Received:
    0
    Location:
    Derbyshire
    Country:
    United Kingdom
    Building Regs were passed a month ago. Part P does apply and am opting to do it myself and get an electriction to certify it ( :confused: if I can do that !! )

    Original plan was for two separate 6mm feeds from house CU. One to supply greenhouse electric/heater and one to garage. This was planned and the cables all plastered in ready for connection to CU. It now is going to be much simpler and shorter (greehouse now being relocated) to take everything to the garage CU and feed all garage and outdoor electricity from there.

    No problem on the two 6mm T&E length/size/construction. They both just go from new house CU up newly plastered and decorated wall and on drums under bedroom floor boards. This was part in exisitng house was done 3 months ago before extension started

    Changing the two 6mm wires plastered in would be big hassle and if safe and within regulations to use both to a 10mm SWA with considerations youve mentioned will be perfect solution

    Will go for the 1.5SWA for the light switching.Four cores for two way switching possibility ( :p hadnt thought of that)

    Will get the building inspectors nod before filling over underground cables.

    Thanks for advice
    Paul
     
  6. andy

    Joined:
    14 Sep 2004
    Messages:
    3,971
    Thanks Received:
    2
    Country:
    United Kingdom
    a spark canot cert your work. he can only cert his work. youll have to pay LABC to cert it for you
     
  7. mr2paul

    Joined:
    8 Jun 2005
    Messages:
    5
    Thanks Received:
    0
    Location:
    Derbyshire
    Country:
    United Kingdom
    Good point, I need to get the Part P form filled in and go down the inspector certifying it route
     
  8. pdcelec

    Joined:
    5 Jun 2005
    Messages:
    707
    Thanks Received:
    0
    Location:
    Birmingham
    Country:
    United Kingdom
    The building inspector will only issue a cert for Part P, he will not produce a BS7671 cert. From experience the building inspector is only there a couple of minutes and has no idea of what they are looking at so they just sign it. A spark could provide a Periodic cert for the installation but not an installation cert.
     
  9. mr2paul

    Joined:
    8 Jun 2005
    Messages:
    5
    Thanks Received:
    0
    Location:
    Derbyshire
    Country:
    United Kingdom
    guess best route is to work with a qualified spark. I can run in cables etc where he tells me and he can do connecting and certifying

    Had electrician connect up the new house consumer unit. Was just a bit concerned because when I called him to explain change of plan to having one supply for outdoors going to the garage and all outdoor circuits to come out of garage he said better make it 10mm 3 core SWA to garage.

    I only thought afterwards that it might not make sense since cable up to the 10mm SWA would only be 6mm. Didnt seem right to go from CU to SWA with 6mm (about 15m) then changing to use 10mm SWA instead of 6mm for about 5M as a solution to a higher load

    This is why I found this and asked question about feeding the 10mm SWA with two separate 6mm T&E which are already available

    Also mentioned Part P to him and asked if he was government approved for it he said "dont worry we will sort that out"

    Guess best bet is to find another electrician, also thought the cost of his previous work was excessive plus what he charged for materials which I have since realised I could have got considerably cheaper from tlc or screwfix

    Paul
     
  10. ban-all-sheds

    Joined:
    27 Aug 2003
    Messages:
    52,052
    Thanks Received:
    2,033
    Location:
    London
    Country:
    United Kingdom
    An electrician can issue a BS7671 Inspection & Testing EIC for someone elses work, and this may well be acceptable to LABC.

    mr2paul - the first, and most important thing is to tell LABC that you will be carrying out the electrical installation work, and see what they plan to do regarding the completion certificate. Bear in mind that as you've paid them a fee it is their responsibility to inspect & test etc for compliance with the Building Regulations. The fee you paid is for them to cover all aspects of controlled work and services associated with the extension. If they are not able to do this for the electrical installation that is their problem, not yours. They cannot charge you any extra to cover the costs of them subbing it to someone else, and they cannot force you to hire an electrician yourself if you don't want to, although in practice it may be difficult for you to show that the work you have done is up to spec without testing it.
     
  11. Big_Spark

    Joined:
    20 Feb 2004
    Messages:
    3,434
    Thanks Received:
    1
    Country:
    United Kingdom
    Lets clarify a few points here.

    Firstly, whilst, in theory, you can create a circuit using parallel conductors to achieve a higher loading capabiltiy, this should only be done if there is no other option. Introducing such circuits to domestic premises is fraught with hazards and should not be encouraged, however as you have these cables in place, so long, as others have noted, that these are the same length, follow the same route, and all coneections will be sound, then it can be done.

    Regarding the Part P issue. Any Electrician can issue a Periodic Inspection and Test Certificate on the installation, they canot issue a completion or installation cert as they diod not undertake the work, however the LABC must accept the certificate from a third party contractor, although they may get funny if the Contractor is not Part P registered themselves.

    The LABC personnel have no electrical knowledge as a general rule, and thus are not legally competent, under BS7671, The Electricity Supply Regs or by anyone elses definition, Competent Persons, as such they MUST accept the certificate if it meets the requirements of BS7671 and Part P of the Building Regs where appropriate.
     
  12. ban-all-sheds

    Joined:
    27 Aug 2003
    Messages:
    52,052
    Thanks Received:
    2,033
    Location:
    London
    Country:
    United Kingdom
    Fraught with hazards?

    You'd not set out to do it, I agree, but it's perfectly in accordance with the wiring regulations, and it can certainly be done, and it is not "fraught with hazards".

    They cannot issue a completion certificate, or a statement that the work complies with the Building Regulations. But an Inspection and Testing Electrical Installation Certificate says what it always has:

    I/We, being the person(s) responsible for the inspection and testing of the electrical installation (as indicated by my/our signatures below), particulars of which are described above, having exercised reasonable skill and care when carrying out the inspection and testing, hereby CERTIFY that the work for which I/we have been responsible is to the best of my/our knowledge and belief in accordance with BS 7671, amended to (date) except for the departures, if any, detailed as follows:

    The factors that anybody has to consider when deciding if they are prepared to make that statement regarding I&T of an installation did not change on Jan 01 2005 - the position is as it always was. It is not, and never was a straightforward thing to do, and it requires and always did require much closer involvement during the installation than is needed for a PIR, but Part P has changed nothing.

    I'm not sure they "must". Since there is no legal definition of who is competent to issue EICs then there is no basis on which someone can say to them "you must accept this". When they are appointing a 3rd party to carry out inspections on their behalf they may well choose to use Competent Person status as a quick and easy way to determine if someone is competent (a very foolish attitude, IMHO, given the way that NICEIC are prostituting themselves), but Part P has nothing to do with EICs, and Part P "registration" has nothing to do with competence to sign EICs.

    They had 2 years and 3 months to prepare for their new responsibilities. If they are charging fees of hundreds of pounds to deal with work properly notified to them and legally carried out by unregistered persons then I'm afraid I have zero sympathy with them over the fact that they can't actually discharge their responsibilities and zero tolerance for the practice of making people pay even more for the services of a 3rd party.
     

Share This Page