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Adding another socket

Discussion in 'Electrics UK' started by Cocat2517, 31 Mar 2019.

  1. Cocat2517

    Cocat2517

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    Hi
    I want to add a third double socket to the front bedroom. I watched this short informative video on radial circuits by John Ward, but want to check a few things first...

    1 Is the setup I have a radial circuit (pretty sure it is)?

    2 If I want to add a third socket coming off from socket 1 then is 2.5mm t&e sufficient?

    3 Do I need to notify building control if self installing?

    4 Are there restrictions on distances/cable lengths in radial circuits? So if I wanted to add a fourth socket in another bedroom, can I run a 10m length of cable (2.5mm?) from the junction box (in loft) to a new socket in another bedroom?

    20190331_225014.jpg

    Thanks!
     

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  2. ericmark

    ericmark

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    In the main radial circuits are supplied from a 20 amp MCB although using 4 mm² cable it could be 32 amp, testing is only way to be sure, with power off open a socket and test between pairs of cables in the socket with a ring final they will be connected with a radial they are not.
    Not if as your diagram you have a 32A supply, yes with up to a 25A supply or using a FCU.
    In the main no, however depends where you live and if the room is considered a special location. Wales and England are not the same.
    Yes in the main a ring final has a 106 meter limit, with radials depends on the max current of supply, for 2.5 mm² with 25A MCB 24 meters, but with a 16A MCB up to 42 meters. It is in the main limited by volt drop, so with 4 mm² with 32A MCB around 44 meters. Using a loop impedance meter the line - neutral impedance can be used to work out volt drop.

    I think with a 32A MCB it is unlikely you have a radial more likely a ring final.
     
  3. Cocat2517

    Cocat2517

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    Sorry, just checked, the sockets are on a 40amp in the consumer unit.

    Sockets 1 and 2 definitely aren't connected to each other or anything else, they are as per diagram, I have traced all cabling. They both have a cable each running to a junction box, then one cable from junction to consumer unit.

    So if the MCB is 40a, what size cable will I require, assuming a 3rd is still an option?

    Location is North Wales.
     
  4. Cocat2517

    Cocat2517

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  5. Taylortwocities

    Taylortwocities

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    @Cocat2517 You need to understand some principles here:
    The MCB is there to protect the cable. It's job is to trip if there is a fault due to an excess load. It basically stops the cable from overheating and catching fire.

    A 40A MCB will usually be used on porabably a 10mm cable, thats the size used for high-power items like cookers and instant heat showers.

    If you have a 40A MCB, with only a single length of 2.5mm cable connecting to the sockets then it is very wrong and downright dangerous. Lets have a look at what is connected to that 40A MCB. Turn off the main switch on the consumer unit, remove the cover and post a photo of the top of the MCB, and also the whole consumer unit.

    As things appear, what has been done is wrong, even before you add yet another socket.

    So, let us have a look at the insides, then we can advise what, if any, steps are needed.
     
  6. Cocat2517

    Cocat2517

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    Thanks, will take some photos now.

    Where does the danger lie in having a small cable connected to a 40a MCB? If the sockets are overloaded? I'm thinking short term safety measures until it's rectified. Currently there's a 120w TV and a 2kw fan heater in one socket and an alarm clock & two 40w lamps in the other.
     
    Last edited: 1 Apr 2019
  7. Cocat2517

    Cocat2517

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    I missed a junction box.

    So it runs from 40a mcb in consumer unit, to a junction box, then on a smaller cable to another junction box, then two cables to two sockets (presumably it had other stuff connected, hence two junction boxes??).
     

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    Last edited: 4 Apr 2019
  8. Cocat2517

    Cocat2517

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    I would hazard a guess that it's 4mm from unit to first junction, then 2.5 all the way from there.

    There are 3 spare 16a mcbs in the unit, would switching the cable over to one of those be safest option?
     

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    Last edited: 4 Apr 2019
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  10. Taylortwocities

    Taylortwocities

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    Probably an old shower circuit that some muppet has utilised without thinking wbout things.. Its probably 6mm² to the first JB (in the loft?) but all the other cabling looks like 2.5mm², and 2.5mm² is too small for a 40A MCB.
    Swapping to a 16A is fine for 2.5mm². It depends on what you have in those sockets as the maximum total current you can draw would be 16amp. You could either physically swop the MCBs, or move the cable.

    Turn off the main switch, and take care when inside an consumer unit. There are still live parts, even with the MAAIN SWITCH off.
     
  11. Cocat2517

    Cocat2517

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    ere's a spare 32A MCB next to the 40A, would that be better than the 16? Is a 2.5 cable okay for a 32A mcb?

    I need a sparky in to fit a 10mm cable for a shower, so while he's there I'll get him to swap the cable over from the 40 to either 16 or 32. I'll do sockets and lights, but I'm not arsing around with the consumer unit itself, I'm a competent diyer, but that's above my pay grade.
     
  12. Taylortwocities

    Taylortwocities

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  13. Cocat2517

    Cocat2517

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    I think all the other sockets (those four 32A mcbs) in the house are on 2.5mm², perhaps swapping all the 32As for 20As?
     
  14. ericmark

    ericmark

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    From your answers you are clearly not competent although competent has now been dropped as a measure of skill, it was the name given to those better than skilled, 2.5 mm² cable does not have one fixed current rating it depends on how installed and if thermoplastic or thermosetting cable, however it is unlikely to be rated at 32A in the main we consider it as rated as 22A unless we have installed it so know exactly the route or there is an installation certificate.

    We are permitted to protect if no branch from the cable and it is unlikely to get damaged and within 3 meter of origin at the detestation of a cable. So it would be permissible to take a 2.5 mm² from a 32A MCB to a single socket, but not to extend from that socket, as the 13A fuse in the plug or two 13A fuses if a double socket is considered as protection from overload and this is what happens with any unfused spur. But that is the only time we are allowed to supply a socket with more than the cable can carry and then the loop impedance of the supply must be low enough so with a direct short the supply overload will disconnect within 0.1 seconds, so loop impedance must be better than 1.44Ω. Today that figure is reduced by 10% which means the cheap Martindale EZ150 tester which passes at 1.5Ω is not good enough so needs a meter costing not £40 but £200 to test the socket is within the regulations.

    Without test gear you must play safe, so the best option is when extending to use a fused connection unit (FCU) so fused to 13A total as then the cheap £40 EZ150 tester will give you a usable result.

    In your case replacing the first junction box for a FCU would then allow you to fit as many sockets as you want, or replacing the MCB for a 20A version would also allow you to extend with 2.5 mm² cable.

    Although you could wire with 6 mm² cable only some sockets will take two 6 mm² cables and there is no way you could spur off as simply not enough room in the terminals of the sockets.

    Judging from your answers and your inability to read and comprehend the answers already given, I would say get an electrician to check over whole installation and modify as required to make safe, if one circuit is so wrong this must ring alarm bells and one must question what other errors there are with the wiring.

    As said it would seem some one has fitted a socket to old shower or cooker supply, and if the cable used was less than 3 meters long that would have been permitted, but then some one has added more and more which clearly is not permitted. This is unfortunately what happens when people do not stop and fill in the minor works or installation certificates, when one fills in the paperwork even if put in the bin after the testing required high lights errors, failure to inspect and test means errors go unnoticed, and it can go unnoticed for years and years, until some one uses high current devices in those sockets. Fact that a socket works is not enough.
     
  15. Cocat2517

    Cocat2517

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    I said I was a competent diyer, not competent with electrics, hence the reason for me posting on here, to find out if it was a simple job of running some 2.5mm cable from one socket to the other, something a competent diyer can do. But after reading the answers I'll be asking the sparky to sort the consumer unit when he comes round for the shower cable, as per my post above.

    Competent means ability to do something to a satisfactory standard, not necessarily be skilled at it.
     
  16. Taylortwocities

    Taylortwocities

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    No no no
    It is very likely that those are on RING FINAL circuits. 32A on 2.5mm is OK for a ring final. Your 40A abortion is a RADIAL circuit. So the whole thing is different.
    Look, you obviously do not have a scooby. You say you have an electrician coming to do some things. Leave it all to him/her.
     
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