1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Fused Spur / FCU with 26 amps?

Discussion in 'Electrics UK' started by andre_xs, 28 Aug 2021.

  1. andre_xs

    andre_xs

    Joined:
    6 Apr 2021
    Messages:
    10
    Thanks Received:
    0
    Country:
    United Kingdom
    Hi Everyone!
    I watched a couple of YouTube tutorials on fused spurs and noticed that they always say that you can only add one socket, because each socket is fused with 13 Amps (x2) and the standard 2.5mm cable takes max of 26 Amps - which nicely fits.

    If you want to make a spur with 2 or more sockets, you need to make a fused spur. I would have thought that the fuse then is 26 Amp, because that's what the cable can take, but they always use 13 Amp fuses in the videos.

    I can see that it makes sense for single-socket extensions (e.g. having the switch for the dishwasher above the kitchen worktop), but for other cases?

    Can someone explain why this is?

    Many Thanks!
     
  2. Sponsored Links
  3. AndyPRK

    AndyPRK

    Joined:
    4 Jan 2009
    Messages:
    5,880
    Thanks Received:
    593
    Location:
    Herefordshire
    Country:
    United Kingdom
    The cable can take 27A, which is under the 26A (13x2)

    The maximum fuse value in that size package is 13A, that is why they are used/recommended.
    A 13A fuse will withstand a lot more than 13A before it will blow.

    So it depends what you intend to plug into the sockets? If its in a kitchen its not a good idea.

    If it was is a kitchen, you could use 4mm cable to get around the limitation. You wouldn't require the fused spur then
     
  4. andre_xs

    andre_xs

    Joined:
    6 Apr 2021
    Messages:
    10
    Thanks Received:
    0
    Country:
    United Kingdom
    Thanks for the reply.
    It was more out of curiosity, to understand the reasoning.
    If I understood you correctly, 13A are mostly used simply because that's what you can buy?
    And from an electrical point of view, it would be reasonable to use a 26A fuse?
     
  5. AndyPRK

    AndyPRK

    Joined:
    4 Jan 2009
    Messages:
    5,880
    Thanks Received:
    593
    Location:
    Herefordshire
    Country:
    United Kingdom
    Yes. or even a 27A fuse
     
  6. andre_xs

    andre_xs

    Joined:
    6 Apr 2021
    Messages:
    10
    Thanks Received:
    0
    Country:
    United Kingdom
    Ok, thanks. Just googled it, there are no 26/27A FCUs, right? Only option would be to use a 26 MCB, as I've seen here in another thread in the forum? (reading right now, came across it a minute ago)
     
  7. AndyPRK

    AndyPRK

    Joined:
    4 Jan 2009
    Messages:
    5,880
    Thanks Received:
    593
    Location:
    Herefordshire
    Country:
    United Kingdom
    The solution is to use bigger cable. 4mm T&E

    You can get 25A MCB's
     
  8. JohnD

    JohnD

    Joined:
    15 Nov 2005
    Messages:
    74,176
    Thanks Received:
    4,283
    Location:
    Crossgates, Europe
    Country:
    Cook Islands
    If you mean you want to take a 26A fused spur off a ring circuit, no, this is not permitted.
     
  9. andre_xs

    andre_xs

    Joined:
    6 Apr 2021
    Messages:
    10
    Thanks Received:
    0
    Country:
    United Kingdom
    Thanks! May I ask why this is the case? Just trying to understand...

    My understanding:

    1. I can make an unfused spur off a ring circuit with a single double-socket. Each socket is fused with 13A, so that the double-socket could draw up to 26A, correct?

    2. But if I want to make a spur off a ring circuit with two double-sockets, I have to fuse it. The reason given is that two double-sockets may too easily overheat the first spur cable from the ring to the first socket, because all 4 sockets may draw up 52A. But the FCUs for this are 13A max. Why not 26A?
     
  10. Sponsored Links
  11. EFLImpudence

    EFLImpudence

    Joined:
    7 Jul 2010
    Messages:
    37,405
    Thanks Received:
    4,195
    Location:
    Retired to:
    Country:
    Portugal
    Yes, it is.
     
  12. JohnD

    JohnD

    Joined:
    15 Nov 2005
    Messages:
    74,176
    Thanks Received:
    4,283
    Location:
    Crossgates, Europe
    Country:
    Cook Islands
    what, with a 26A MCB?
     
  13. AndyPRK

    AndyPRK

    Joined:
    4 Jan 2009
    Messages:
    5,880
    Thanks Received:
    593
    Location:
    Herefordshire
    Country:
    United Kingdom
    good point.

    You shouldn't over load one end of a ring.
     
  14. EFLImpudence

    EFLImpudence

    Joined:
    7 Jul 2010
    Messages:
    37,405
    Thanks Received:
    4,195
    Location:
    Retired to:
    Country:
    Portugal
    However it might be achieved.
     
  15. ericmark

    ericmark

    Joined:
    27 Jan 2008
    Messages:
    18,572
    Thanks Received:
    1,743
    Location:
    Llanfair Caereinion, Nr Welshpool
    Country:
    United Kingdom
    This has been a problem for years, the standard 16 amp fuse [​IMG]is larger than the 13 amp fuse, so it will not fit in a standard FCU, it would be good if you could have a German socket [​IMG] and a 16 amp fuse next to it, so we can use appliances designed for Germany, however in real terms a 13 amp fuse will for a short time take over 13 amp, and likely any appliance rated 3.5 kW would not rupture the fuse as not used for long enough.

    The rating for a double socket seems to depend on make and type, filtered sockets and sockets with other extras are often rated at 13 amp for the pair, many are rated at 20 amp for the pair, seems it is considered we would not use two 13 amp appliances together, they have not seen my kitchen, with two cup boilers together, ready for the coffee making in the adverts.

    The problem is when we moved from 7/0.029 cable to 2.5 mm² cable we dropped from around 2.9 mm² and at the same time went up to 32 amp instead of 30 amp, plus other mods through the years like reducing the live pin size at top and covering with plastic to stop finger contact, which also reduces the heat the pin can dissipate, so running an immersion heater from a 13 amp socket is not recommended due to the time it draws the 13 amp for.

    So we can over load the ring final at the ends, as the current is not equal shared, the cable needs to be rated 20 amp, and be 2.5 mm² unless mineral insulated where 1.5 mm² is allowed, but the whole system works on near enough engineering, and we are told any non portable appliance should have a dedicated supply if over 2 kW, so with oven, washing machine, tumble drier, dish washer, immersion heater all with dedicated supplies it is unlikely the ring final will be over loaded, my leaf blower is about the only item I have which is portable and could be used for an extended time over the 2 kW limit.

    Yes I know we only seem to put the immersion heater on a dedicated supply, however since in theory at least the oven is over 2 kW and too heavy to be classed as portable, to produce a fused outlet for the oven would be against the BS 7671 recommendations in the appendix. So we don't have them.

    Although we could say there is a chance of over load on the ring final, experience shows us this is very rare, the 32 amp supply in the main with a domestic property with the limit of 106 meters of cable in the main works well, and more to the point is cheap, with radials to each socket and 16 amp RCBO's on each radial even if some sockets doubled up, likely looking at 6 to 20 radials per house compared with 1 to 3 ring finals. At around £20 each the cost of RCBO's plus the cost of cable, would add a lot to the wiring bill. It need three radials to replace one ring final, and once you have more than 1 socket you have to consider over load tripping as well as volt drop on the cable.

    So yes there are faults with the ring final system, but the plus points are greater than the minus, I does seem there is a move from the ring final, even the simple socket tester with loop, the lowest reading is around 1.7Ω to 1.9Ω depending on make, and pass mark is 1.38Ω, so clearly really made for 16 or 20 amp supplies not our 32 amp supply.

    But it has worked well since the second world war, so see no reason to change now.
     
  16. AndyPRK

    AndyPRK

    Joined:
    4 Jan 2009
    Messages:
    5,880
    Thanks Received:
    593
    Location:
    Herefordshire
    Country:
    United Kingdom
    sparks do seam to be moving to radials (sadly) The testing is too much for them.

    They have a radial for upstairs, and another for downstairs living area.
    Hopefully a seperate 32A circuit for kitchen
     
  17. EFLImpudence

    EFLImpudence

    Joined:
    7 Jul 2010
    Messages:
    37,405
    Thanks Received:
    4,195
    Location:
    Retired to:
    Country:
    Portugal
    Why sadly? There is no point today with MCBs for the UK ring with its special conditions.

    I wonder if your reasons for liking the ring circuit actually relate to its properties.
     
Loading...

Share This Page