3 gang socket outlets - can they be used for "daisy chain" spurs?

Discussion in 'Electricians' Talk' started by diymostthings, Jun 29, 2013.

  1. diymostthings

    diymostthings Well-Known Member

    I notice these MK units have a 13A fuse built in. I presume therefore that they can be used rather like a FCU. I would like to add two in a daisy chain fed from a single (ring main) socket to avoid upheaval.

    Any comments/experience with these gratefully received!

  2. seneca

    seneca Screwfix Select

    I'm not sure that the 13a fuse protects all 3 sockets, maybe only one of them (the one that's extra from a normal double socket outlet) Although i've fitted a few of them to replace double sockets i've never got around to checking whether the fuse protects all 3!) If not you'll need tofeed them from a fcu.
  3. diymostthings

    diymostthings Well-Known Member

    OK Seneca - I'll have to think how to check this by looking at the internal wiring. Assuming all three are protected by the 13A fuse, I'll go ahead and daisy chain. Many thanks.

  4. unphased

    unphased Screwfix Select

    Hi diy

    You cannot "daisy chain" as you put it, 3-gang 13A fused sockets. This is a spur-off-a-spur situation. The sockets would be on a radial spur. Not allowed. The reason for the 13A fuse in the socket is to prevent overload of the accessory, not overload of the circuit. Think about it. Its no different to daisy chaining a load of single sockets. You can't do it. 3-gang sockets are really pointless, far easier to install 2 x double socket side-by-side. Either extend the ring or put an unswitched fused spur in and come off that. Or if its already a radial circuit then thats different. 20A mcb at the board. Put as many sockets as you want in.

  5. seneca

    seneca Screwfix Select

    Yes, I suppose even if the fuse does protect all 3 outlets putting another one on would still be like putting 2 ordinary sockets on a spur. I don't really think the 3 gang sockets are pointless though UP, very handy where the load is going to be small, eg  av equipment etc, they do have their uses.
  6. J.P.

    J.P. New Member

    I plug one of those 3 gang sockets with a 5 amp Plug on the end into my 5 Amp SO in front room Sen - it operates the Christmas Tree and aux low draw lights. You just switch it off at the plate when going to bed.
  7. seneca

    seneca Screwfix Select

    You're talking about a 3 way extension lead JP, we're talking about the fixed 3 gang socket that replaces an ordinary 1 or 2 gang socket.
  8. J.P.

    J.P. New Member

    Oh right - sorry Sen.
  9. Lokkars Daisy

    Lokkars Daisy New Member

    Two triple sockets each protected by its own 13A fuse is no different from one twin socket spurred off a ring circuit. So yes two daisy chained is ok.
  10. diymostthings

    diymostthings Well-Known Member

    Thanks for that unphased

    "...The reason for the 13A fuse in the socket is to prevent overload of the accessory, not overload of the circuit..."

    Surely that can't be right. The accessories are protected by their own individual fuse in their plugtop - the fuse in the socket can only be for protection of the circuit cables?

    Hope you see my logic, but willing to be shot down!

    I guess I could always ask MK.

  11. diymostthings

    diymostthings Well-Known Member

    Thanks Lokkars Daisy, that's what I was thinking but as always willing to be shot down!

    The things you plug into the socket are protected by their own fuse in their respective plugtops - so the only value in having a fuse in the actual socket must surely be to protect the cabling to the socket? I suppose without that fuse in the socket you could have three items plugged into the socket with a 13A fuse in each plugtop, making a theoretical current demand of 39A! -  Above the 32A cutout of a ring main. With a twin gang socket (no fuse) the demand would be a max of 26A before a plugtop fuse blew - below the 32A cut out.

    Sorry not explaining it well but do you see my logic?

    Bottom line I think you agree that you can treat the 3 gang socket as an fcu.

  12. unphased

    unphased Screwfix Select

    The logic is sound. A single socket with one 13A appliance plugged in so 13A load on the socket. Twin socket with two 13A appliances plugged in can draw up to 26A if both running full tilt. Now. Triple unfused socket with three 13A loads plugged in could in theory pull up to 39A. Too much for the circuit and the accessory. So a 13A fuse in the three-gang socket ensures that only 13A can be loaded on to it. Protects the accessory and limits the load at that point on the circuit. So a three gang socket without a fuse in it would potentially allow 39A to be drawn at that point overloading the circuit and the accessory.

    I think these three-gang sockets are pointless because a twin socket allows 26A but a three-gang only 13A. What is the point? Better to have two double sockets side-by-side.

    You cannot treat the three-gang socket like an fcu because the circuit is not passing through the fuse, it loops on and off again hence no limitation in the circuit itself. If the fuse were to break in the three-gang socket it doesn't cut the power to the remaining section of the circuit. Remember that the fused spur is protecting the whole of the radial circuit it is supplying. This is why, for example, you cannot put loads of single sockets on an unfused spur. Each single socket is in theory limited to 13A but the regs say you must limit an unfused spur to one single or one twin or even one triple. If you start to put three-gang sockets in and say have a 13A appliance plugged in each you have a circuit overload. You cannot bend the rules like this. You must only use one unswitched spur off a ring else you need to put an fcu at the point you want to spur from. Hope this helps.

  13. diymostthings

    diymostthings Well-Known Member

    Thanks unphased for that quick and full reply -couldn't you sleep either? (too hot last night!).

    That makes a lot of sense - I'll prob keep the 3G's but use an fcu for two daisy-chained spurs.

    kind regards

  14. diymostthings

    diymostthings Well-Known Member

    I spoke to MK (very helpful). Yes the 3G sockets CAN be treated as a FCU for the purpose of adding another socket spured off the 3G. The 3G fuse must therefore be in the live through the socket and not just the live pins within the socket. Thanks for all your comments - case closed!

  15. unphased

    unphased Screwfix Select

    It is a fundemental requirement that fuses are only allowed in the phase conductor. MK are wrong when they say a 3-gang socket can be treated as a fused connection unit (FCU). A cable spurred off a 3-gang socket IS NOT PROTECTED BY A FUSE. The fuse in a 3-gang socket is limiting the current from the socket to 13A. That is any appliance plugged in to it, not what is looped off it. If you cannot see that then you have not grasped the basics.
  16. diymostthings

    diymostthings Well-Known Member

    Thanks for that unphased - I doin't think I misunderstood MK (although it is possible). Anyway for my project I fitted a FCU after the 3G socket (itself on the ring) and before the socket outlet I want. I'm now going to try to find out exactly how and where that fuse in the 3G is placed - do you happen to know?

    Thanks again.

  17. Sean_ork

    Sean_ork Screwfix Select

    the single fuse is before all 3 outlets - fuse blows = all outlets dead
  18. seneca

    seneca Screwfix Select

    Correct, so it's just like using a 3  or 4 gang extension lead, the whole lot's fed through the one fuse.
  19. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Don't think the case is closed.

    Thinking logically, if the fuse were to blow in the 3G socket, then in your scenario it would cut the supply to the rest of the ring. You would therefore have left, two radials on the ring 32A MCB both ending at the blown socket. That isn't allowed.

    To use the 3G as a spur extension, you would need to connect up to one of the pins(and there will be no facility for this).

    I think you'll find the ring carries on through, and the group of sockets are themselves fused spurs from that line.

    Maybe now the case is closed?

    Mr. HandyAndy - Really

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