Consumer Unit wiring in garage - is this safe/legal?

Discussion in 'Electricians' Talk' started by jimwillsher, Sep 19, 2011.

  1. jimwillsher

    jimwillsher Member

    Hi folks,

    We moved into this 2007-built house a few months ago and I'm trying to document the actual wiring, as opposed to what the labels on the CU claim. I've discovered something that I don't particularly like and would value your thoughts. I'm no spark, just a DIY-er.

    There's a 16A breaker in the CU labelled "boiler and garage door". There's two live wires connected into it. I had hoped this would be a ring. Upon closer inspection it's like this:

    Wire 1 (2.5mm t&e) goes to a socket into which the boiler is connected.
    Wire 2 (2.5mm t&e) goes to a double socket (currently unused), then another double socket (fridge and freezer) then another double socket (battery drill charging) then another double socket (currently unused).

    Effectively, spur after spur after spur. I didn't notice this initially, as I could see two cables running to all the sockets. I assumed this to be a ring but I now realise it's a chain.

    I'm less worried about the legality than I am about the safety. Is this setup an accident waiting to happen, or will the 16A breaker be a suitable safeguard against overloads and fire risks?

    Many thanks,


    PS Updated in light of analysis. When disconnecting live wire from back of socket nearest the CU, the fridge/freezer still work but most other things do not.

    Attached Files:

  2. spinlondon

    spinlondon Well-Known Member

    The circuit you describe is a Radial.
    Although it is labled up as boiler and garage door, it might have been better labled up as sockets.
    The rating of the MCB is fine to provide both overload and fault protection, anything higher and (dependant on how the circuit cables are installed) it might not provide fault protection.
    2.5mm² T&E has a current carrying-capacity of between 13.5A and 27A, depending on method of installation.
    It may well be that a 20A MCB could be used, however the resistance at the furthest point on the circuit also has some bearing on the selection of protective device.
    If the measured Zs (resistance) at the furthest point on the circuit, is above 2.3ohms (1.84ohms corerected), then a 20A MCB would not be suitable.
    It would be perhaps a simple matter to alter the circuit, to make it a Ring, allowing you to install a higher (up to 32A) rated protective device.
    However, doiing such, may lead to further complications, such as RCD protection, and Part P notification.
    As it stands, it sounds as though the circuit is adequately protected, and unless you start using high current equipment, there is no need to alter it.
  3. J.P.

    J.P. New Member

    I wonder if the chap has got a spare way in that DB?
  4. jimwillsher

    jimwillsher Member

    spinlondon, many thanks for your reply and explanation. I've since done some more digging through trial and error of disconnecting wires from sockets etc. and seeing what's still live, and I've revised my understanding of how it's connected. I've also been into the loft and traced the wires. Wiring 2.jpg (hopefully attached) is how it's wired up.

    My thinking is this: The breaker is labelled "boiler & garage door", and technically that's correct since there's a direct wire to each. However my suspicion is that builder forgot to include any sockets in the garage, and has therefore daisy-chained everything onto the end of the garage-door wire.

    I currently have access to the coombed ceiling space due to some plasterwork we're having re-done, and I have the opportunity to get access to the right parts of the run. On my attached drawing the red line is the wire that I can lay if appropriate. My understanding is that this would then change the circuit into a ring since all the sockets would be dual-wired and both ends would terminate in the CU. Would you see this as being a worthwhile exercise?

    If I do run this extra wire to the CU to complete the loop, are there implications for:

    - The breaker being a 16A
    - The boiler being connected to the same breaker (the boiler itself has a fused 13A plug on the end).

    Thanks again,


    Attached Files:

  5. jimwillsher

    jimwillsher Member

    Nothing spare, but I can run a wire to complete the ring - see my next post.
  6. spinlondon

    spinlondon Well-Known Member

    The implications are, why do you want to do this?
    At present, it appears that you have a perfectly acceptable circuit arrangment.
    The protective device is adequately rated to protect the cable and as far as I'm aware is adequate for the expected load.
    There's no point in altering the Radial to a Ring, unless you intend uprating the CPD.
    You only need to uprate the CPD, if you expect the load on the circuit to be increased.
    One thing I would suggest, is that you check the fuse in the boiler plug.
    13A is not usual, it is more common for a 3A fuse to be used.
  7. jimwillsher

    jimwillsher Member

    Many thanks again. My only reason for doing this is that I've always understood this method to be "less safe" than a ring, in that the current from all sockets is going through a single point - similar to the limits on spurs I imagine. But I agree, it's probably a lot of effort when the current system is safe, especially as it's a 16A breaker.

    And you're right, it's a 3A fuse in the boiler.

    Many thanks for your help, appreciated. I'll leave well alone :)

  8. J.P.

    J.P. New Member

    What's a CPD Spin?
  9. seneca

    seneca Screwfix Select

    It all seems like a perfectly normal radial circuit. Radial's are not less safe than rings provided the correct fuse/circuit breaker is in use, in the case of 2.5mm. t/earth this would be 16 or 20 amp. Leave it alone would be my advice Jim!
  10. seneca

    seneca Screwfix Select

    Circuit protective device J P.
  11. J.P.

    J.P. New Member

    Oh right. Cheers Sen.
  12. Crazy Eddie

    Crazy Eddie New Member

    Always thought radials were safer than rings, full stop.
  13. spinlondon

    spinlondon Well-Known Member

    Not really, easier to test maybe, easier to fault find, but not particuarly safer.
  14. seneca

    seneca Screwfix Select

    Jim, earlier you said you thought  radials were "less safe" than rings, now you're saying you thought radials were safer than rings, make your mind up!
  15. neil2jo

    neil2jo New Member

    Only just read your post and skipped a lot of the answers after the 1st few replies, but for info as other have said the 16amp should protect the usage of the sockets indentified, however regs say that each circuit should have a dedicated fuse/mcb, therefor isolation can be identified for the correct circuits and for the purpose of electrians testing correct reads of Z's and continuity can be achieved

    Therefore given your situation you could do 1 of the following

    a:  create a ring from the 2 radials you have, by joing the ends of the radial togther using 2.5mm t&e, therefore requiring the MCB to upped a 32amp...changing the design of circuit requires a reg electrican to sign off ;)

    b: seperate the 2 radials and all being you have a spare way (slot) on your consumer add another 16amp/20amp fuse/mcb for the 2nd radial.... changing the design of circuit requires a reg electrican to sign off ;)

    c: Leave it and pretend you dont know any better :(

    Please note whilst you may have an RCd board 2003, likley some circuits are not protected by RCD, any circuits buried in walls (most) require that they are protected by RCD's, so if you dont touch and presume you dont have an RCD, everything is fine, touch/alter circuits and all of sudden you  need RCD protection
  16. neil2jo

    neil2jo New Member

    anyone who is NICEIC and attended 17th courses since its launch may well have had the bonus info thrown at them, that is likley over the next few years that the UK will work towards radials, in line with europe, who don't install rings.

    It is felt that radials are easy to indentify risks/problems....a very quick example is if 1 of the live/phase comes loose in a ring circuit, the socket will continue to work at the risk of arcing etc, no one might find out and problem goes on as 1 phase is still connected and therefore all sockets work, however the potential load of the circuit is now on perhaps 100m of 2.5mm taking all kitchen appliances + house hold equipment.
    Given the same senario in a radial, the customer would spot a non working socket or more and call a sparky.
  17. sparky Si-Fi

    sparky Si-Fi Well-Known Member

    Seggragation of circuits is an inspection aspect, but without spoutin' like a regs book, the cable is protected for the loads it will intentionly supply,

    A boiler is looking at 1A tops, with the pump being the main drag,as for the garage door and the double sockets, as stated its all fused to protect

    Leave it as it is.

    One thing I do not encourage, is telling folk step by step to go rodgering about changing radials to Ring finals in a chat room

    Changing the design of a circuit requires a registered spark to sign it off ;)

    No spark is going to stick his neck on that chopping block.
  18. sparky Si-Fi

    sparky Si-Fi Well-Known Member

    The IET are not looking into withdrawing the Ring final circuit,

    The never ending souring price of copper may have something to do with it, as this was the reason for its introduction.

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