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Unfused Spurs from a Ring Circuit

Horace Charles

I am not an electrician but have electrical knowledge and some knowledge of ring circuits and the wiring regulations. I would like to understand from expert readers some points about an unfused spur from a ring circuit.

As I understand it the regs say that an unfused spur in 2.5mm cable from the ring circuit may feed only one single or twin (or triple?) socket OR one fixed appliance via a Fused Connection Unit (FCU).

BUT if instead of feeding a single fixed appliance, that FCU fed several sockets, would such an arrangement comply with the regulations. The combined maximum current to those sockets would of course be limited by the FCU 13 amp fuse and RCD protection is assumed at the Consumer Unit.

This limited current capability of sockets fed in this way might be restrictive, but might be OK if low current loads are connected to them e.g TVs, computer power supplies, electric armchairs etc.

I would like to understand if such an arrangement would be feasible before I call in a qualified electrician to quote for it. The reason for asking is that it would allow the provision of surface mounted sockets thus avoiding the need for disruptive cable chases in the wall.

Thanks for any feedback you may offer

  • 0 in reply to Horace Charles

    "assumed to be on the ring circuit" - that is definitely worth checking before you go too far down that route - it's surprising what lengths some people went to to save a couple of metres of cable - I've seen many a house where the developers ran a ring around the first floor floor void and every socket downstairs was on a spur dropped down from it. Even seeing two cables behind a socket is no guarantee - older regs used to allow two singles on a spur, and they're often then "upgraded" to doubles without proper consideration, or just done by people who never understood the rules in the first place.

       - Andy.

  • 0 in reply to AJJewsbury

    Thanks Andy for your reply. In the absence of easy visual access to check that I'm hoping the electrician will be able to determine that by resistance tests? Its a bit of a minefield ! Maybe Chris's tongue in cheek trailing socket approach is starting to look appealinng

  • 0 in reply to Horace Charles

    Splendid! That makes sense.

    I can see the point about decor and making good. It might still be relatively easy to extend the ring. Something has to go next to the existing sockets, but there could be another socket, or even a blanking plate. If there are a few inches of slack in one or other side of the ring, or room in the backbox so that (maintenance-free) terminal blocks can be used, extending the ring should not be a problem. Granted, it uses more cable, but two lengths of 2.5 mm² will sit comfortably side by side in mini-trunking.

    That is something for your sparks to find out.

    AJJewsbury said:
    "assumed to be on the ring circuit"

    My thoughts entirely, but it seems unlikely to be a radial. Let's not get too technical and confuse Horace. :-)

    I hope, Horace, that you now feel more clear about the way ahead. If not, feel free to ask.

  • 0

    Once a spur is taken via a 13 A FCU, it becomes a fused radial and may supply multiple socket-outlets, subject to correct cable sizing, RCD protection, and load limitation by the fuse. The main concern is future misuse with higher-power appliances, so inspection/testing of the existing ring and competent design are essential.

  • 0 in reply to Anas SAHILI

    Thanks Anas for your feedback

  • 0 in reply to Chris Pearson

    Thanks Chris and all other respondents

    My conclusion is that although technically permissible within the regulations, feeding multiple sockets in the way I envisaged would be considered "poor practice" by electricians because of the potential consequences of the plugging in of high current items (FCU fuse blowing).

    So I will be discussing with the electrician, the option of extending the ring at the existing flush socket, to "break out" into new surface sockets all connected in the ring.

    Some disruption to the wall decor might be unavoidable, but it has to be done right.

    Thanks again to all for your feedack

  • +1

    You could use a 4mm cable then you won't need a switched fused spur so long as you are confident that the point in the ring you are connecting to is not going to get overloaded. If it is for a few convenience sockets that won't get multiple high usage appliances plugged into them such as heaters then you are fine.  Or it is pretty straight forward to extend the ring from a double socket if it is on the ring already, it's just a couple of crimps or the like behind the socket if the box is deep enough and the ring is not already too long.

    Gary

  • 0 in reply to Chris Pearson

    In reality, modern computers don't take much power. Gaming machines may be several hundred watts, but laptops much less.

    During lockdown, I had a 5A rated extension lead (with a 5A fuse in the plug) powering a 4-way and a 3-way extension lead, for my home computer and company laptop, plus all their peripherals.

    Nothing bad happened.

  • 0 in reply to aligarjon

    Thank you for your feedback. I will be talking with an electrician to look at the feasibility of extending the ring at the existing flush socket.

    Re your suggestion to use 4mm cable, do the regs allow an unfused spur of that cable size to feed more than one socket.? I understand it has greater current carrying capability which I'm guessing is greater than the 30 amp (or 32 amp In a new CU) protective device ?

    I see also you mention a "switched" FCU. In my original idea would it need to be switched ? I'm just technically curious and I will be pursuing the ring extension approach.

    Thanks again for your feedback 

  • 0 in reply to Simon Barker

    Thanks for your feedback. I understand your point about today's devices being relatively low current demand items.  That was my thinking from the outset.

    But I can see from previous responses that electricians would prefer to add sockets by connecting them in an extended ring circuit.

    I suppose there will always be the possibility of a future owner of the house, who is not aware of the 13 amp FCU limit, plugging electric heaters in to the sockets if the central heating fails ?

    Thanks again for your feedback 

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