Plug sockets

Discussion in 'Electrics UK' started by lizziec, 24 Feb 2006.

This topic originated from the How to page called 3. Electricity.

  1. lizziec

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    I have two plug sockets that don\\\'t work. Is this dangerous? Should I have the whole system checked out?
     
  2. Nestor_Kelebay

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    Could it simply be a blown fuse?

    Also, on this side of the Atlantic Ocean we have something called "Ground Fault Interrupt" receptacles (or GFI, for short), and you may have something similar if this is a newer house you're living in.

    What GFI receptacles do is monitor the current going through the live and neutral wires. If there's an difference in the number of electrons flowing into an appliance versus the number coming out, then the GFI presumes the difference is due to a short circuit to ground, and shuts off the power to the receptacle. And, of course, other electrical outlets wired to a GFI will also be protected by the GFI the same way.

    Perhaps you have a tripped GFI receptacle, and you simply need to reset it to get all of the receptacles working again.

    I'd post in the Electrics forum. The guys there will be able to help you check for all the PROBABLE causes yourself. However, if the problem persists, then I would call someone to check those two receptacles out.

    At this point I wouldn't presume the problem is anything more than a blown fuse (or something similar), and neither dangerous nor cause to have the whole system checked out.
     
  3. Steve

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    Just a note for Nestor. This side of the pond we call them RCDs (Residual Current Devices) which monitor the phase and neutral currents, and an imbalance trips the circuit. I know over there they are keen on installing them into individual sockets, but here they are more often installed protecting the whole installation, or a part of it, by installing them in the main distribution board in homes. Whether the whole place is protected by it depends usually on grounding (earthing) arrangements.
     
  4. JohnD

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    It's fun educating Nestor! ;) just pulling your leg :D

    In the UK we generally connect our sockets on a ring main. One of the characteristics is that each socket has a supply coming into it from both sides, and another characteristic is that a large number of sockets are protected by a single 32Amp MCB (or fuse)*

    This means that if a fuse or MCB has failed, then all the sockets on that circuit (typically one floor of a house) will stop working, as will appliances connected without a plug, such as extractors.

    Another characteristic is that (unfortunately) if a single wire in the circuit is damaged or disconnected, all sockets will continue to work (though cable loading may theoretically become unbalanced). Only if cables from both sides of a socket are damaged or disconnected will that socket stop working.

    If a single socket stops working it is more likely a badly wired or damaged socket, possibly where the terminals were not tightened adequately or the wires not inserted correctly, and have subsequently overheated. It won't be a blown fuse or tripped MCB. It could be (but probably isn't) multiple damages to cable.


    *Go on, ask me how a 32A MCB protects a 3A table lamp! :LOL:
     
  5. Nestor_Kelebay

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    No, John, I trust you know your wiring. If you explained how a 32 amp module could protect a 3 amp table lamp, then what little of it I understood would promptly be forgotten.

    I had no idea that your wiring would be so completely different than ours.

    The thought that you might not even have individual fuses on each circuit didn't even cross my mind.
     
  6. JohnD

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    Hope you don't mind - I'll tell you anyway! There's a fuse in the plug!



    Every socket outlet is fed by two 2.5mm sq twin and earth cables, one from each side. The cables are run in a ring which starts and ends at the circuit fuse in the consumer unit, and an (almost) unlimited number of sockets can be installed in the ring. The supply is fused at 32A. However - every plug contains its own cartridge fuse, which is sized appropriate to the appliance. Most common are 3A, 5A and 13A (which is the max). So every appliance can be appropriately fused. But every plug, and every socket, is the same size and shape, regardless of its load. The (then) 30A rating was chosen on the grounds that most people had a 2kW electric fire, a few had a 3kW fire, and some also had an electric kettle or toaster. At the time no-one had a dishwasher and few people had electric washing machines (!) but they were expected to become popular.

    When I read the old Electrical books from 1946 I was really impressed at the thought that went into it (we had 6 years of total war, many homes destroyed by bombing, with no supplies of copper wire or electrical equipment available for housebuilding, and all the tradesmen drafted into the forces or working in munitions factories, so needed an entire rebuilding and renovation plan). So we were starting with a pretty clean sheet, and could standardise and supercede the many different sizes and shapes that had been designed by different manufacturers, or used for different purposes. As well as the ring main, and the standard fused plug, the square-pinned plug was introduced at the same time as it can be manufactured to give a more relable contact, resistant to wear; and the cable was put at right-angles to the pin axis to discourage people using the flexible cord to pull plugs out of their sockets. All plugs are earthed, and the earth pin is larger and longer than the others so that the earth connection will make first and break last. The socket is shuttered so that until an earth pin has entered, the phase and neutral orifices are blocked so a child can't poke a nail in and make contact with live parts. You can tell I think It's a terrific design.

    The plug is rather over-engineered, and quite big, so when we go over to a single European standard it will become obsolete (I worked in the Distribution and Supply industry for some years, and one of the principles of the new European standard is that it shall be completely new, so that no one country has an advantage).
     
  7. jbonding

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    nice post ;)
     
  8. JohnD

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    ...and furthermore, in a later development, the plug pins are partly shielded with plastic, so that when a plug is partially withdrawn from the socket, the exposed metal part of the pin can't be touched until it has been withdrawn enough to lose contact with the live part of the socket.

    ?is there no end to the benefits? ;)


    ...and because it is a three-pin plug, with a larger earth, it is impossible to insert it incorrectly; so the position of the phase and the neutral conductors are always known, enabling a single-pole switch, if used in the flexible cord or the appliance, to be always in the phase conductor.

    (drones on, and on, and on...)
     
  9. SamySnake

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    I wish you were my lecturer John D.

    (wanna give me a job!?)
     
  10. Chris.J

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    Off on a slight tangent : --
    Some new houses are using the old 5A sockets as outlets for table lamps. Several per hall/lounge/dining room, all controlled by one switch (per room or per floor). Fed from a 6A MCB. Sometimes done instead of wall/ceiling lights.
    Anyone else come across this arrangement?, are they permissable under the regs?
    Should fused or unfused plugs be used (fused are expensive, unfused cheap)?
     
  11. JohnD

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    They are fed from a 5A fused supply, so don't need to be fused at the plug. An ordinary ceiling lamp is also fed from from a 5A (or 6A) fused circuit, and in the same way, the switch and lampholder don't need to be additionally fused. The round-pin lighting sockets are used specifically to prevent them being consused with a circuit that needs fused plugs. It is very important that you don't put 5A sockets on a ring main (but you can put them on a 5A fused spur).

    BTW in the theatre we also use round-pin 15A plugs for stage lights, these are on a sort of radial where the overload protection is at the supply end.
     
  12. hairyjon

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    Lizziec's question has sparked ('scuse the pun!) of a very interesting history lesson from JohnD! Thanks John -Hairyjon
     
  13. danlightbulb

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    That is the most interesting thing ive read in ages. Great British design at its best (...pulls stiff upper lip pose).
     
  14. JohnD

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    <--- (blushes with modest pride) :oops:
     

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