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Single mains socket - on two fused circuits !?!

Discussion in 'Electrics UK' started by My Key, 16 Aug 2018.

  1. My Key

    My Key

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    Hello All,

    I recently moved into an independently built 1960s house which was very high spec for the time. The previous occupants replaced the kitchen and it looks like an electrician might have done the wiring because a new CU was installed with a single RCD for all the kitchen sockets. The original wiring uses a Wylex type fuse box. I suspect a previous owner of doing some DIY electrics in the house.

    I have just come across an original single mains socket in the kitchen that was not controlled by the CU. It has two wires attached and so I assumed it was part of a ring main. By pulling out fuses, I initially failed to find the fuse for this socket. After several attempts, I realised that I needed to pull out two fuses to completely isolated the socket.

    This looks very bad to me. Am I right? Do I need to get in a qualified electrician to investigate or is it something that a fairly competent DIYer like me might be able to sort out?

    Btw, in the next room I have also come across a double light switch that has one switch on the downstairs light circuit and one on the upstairs like circuit. That taught me a lessen about properly checking that everything is isolated.

    Any advice would be gratefully received.

    Thanks,

    My Key.
     
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  3. EFLImpudence

    EFLImpudence

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    Yes, it would appear someone has mixed up the four cables of two ring circuits.
    Connecting the line(live) legs of both rings to the two fuses instead of the same one.
    This could be dangerous and must be rectified immediately.

    Careful, this will affect all the sockets on these two circuits, which I might guess is all of them except the ones on the kitchen CU

    If you didn't understand the above, then get an electrician.

    Yes, common and unavoidable. Lesson learned.
     
  4. JohnW2

    JohnW2

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    Indeed, and it's certainly not the first time it's happened. When I bought my present house, I inherited a pair of ring circuits wired like that, and it was only because I was diligent in 'testing for dead' when I worked on one of the circuits that I discovered (and rapidly remedied) the error!

    If circuits are like that after initial wiring then that's pretty 'unforgiveable', since it implies that no proper testing was done at the time. However, I think it sometimes arises during subsequent testing/inspections if (very foolishly, I would say) conductors are removed simultaneously from two or more fuses/MCBs in order to undertake testing.

    Kind Regards, John
     
  5. My Key

    My Key

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    I have found the report by the electrician who did the work in the kitchen (5 years ago). I suspect that this qualified electrician was working on mates rates and has done the bare minimum to be able to sign-off on the work in good conscience (not judging, I suspect the previous owners couldn't afford to do more). If he made the mistake with the two circuits then it has "only" been like it for 5 years, otherwise it has probably been like that for >15 years.

    Anyway, all that is largely irrelevant to me. I am going to get a qualified electrician to come and inspect and rectify the problems as soon as possible.

    Thanks for your quick replies and advice.

    My Key.
     
  6. ban-all-sheds

    ban-all-sheds

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    ;)
     
  7. ericmark

    ericmark

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    I have seen both 2 x 32A fuses feeding on ring final and 2 x 16A fuses feeling a ring final, although not normal the latter is likely better than a single 32A fuse and is not a problem, however the former is a problem as there is potential for an overload.

    So in your case two labelled 15 or 16A fuses would not be a problem, so if 30 or 32A fitted simply down grading fuses would make it safe.

    I have also down graded when I have found what should be a ring final is in fact two radicals, or when a 4mm radial has been extended with 2.5mm cable.

    Before 1966 it is likely there is no earth to lights, so all property built before then and not rewired does need an EICR to highlight faults, I would have expected it to have been recommended when you bought the house.
     
  8. JohnW2

    JohnW2

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    True (although, in practice, overload is actually pretty unlikely, given the rarity of 30/32A OPDs on sockets circuits ever operating as a result of overload).

    However, the greater concern, being discussed in this thread, is obviously the danger (in terms of isolation/'making dead') associated with any circuit which is fed from two OPDs of any rating - since that danger would exist whether it was 2 x 6A or 2 x 32A.

    Kind Regards, John
     
  9. John D v2.0

    John D v2.0

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    I would say it's better but not compliant with the regs. Having more than one ocpd would create difficulties, especially with no way to document it on the forms.
     
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  11. JohnW2

    JohnW2

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    Not only non-compliant (to not have a 'single point of isolation' for a final circuit would presumably not be compliant), but frankly dangerous - for the reasons discussed. People are simply not used to having to operated two MCBs (or remove two fuses) in order to make a circuit safe to work on - and, although they should, not everyone 'tests for dead' (or does so in an adequate manner).

    Kind Regards, John
    Edit: crucial missing word added!
     
    Last edited: 17 Aug 2018
  12. ban-all-sheds

    ban-all-sheds

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    "to not have a 'single point of isolation' for a final circuit would presumably not be compliant"?
     
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  13. JohnW2

    JohnW2

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    Yep, thanks for noticing - now corrected.
     
  14. ban-all-sheds

    ban-all-sheds

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    No it isn't... Now it is.
     
    Last edited: 17 Aug 2018
  15. ericmark

    ericmark

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    To isolate one must disconnect all live circuits, so in most cases since the MCB or fuse does not disconnect the neutral in most cases this means the main switch or RCD. OK some RCBO's today do switch the neutral, but also using MCB's you could use double pole.

    However we need to assess risk, so given that home owner knows there are two fuses supplying a circuit which is the safest DIY method around the problem? Swapping 32A to 16A does not involve opening the fuse box, so to my mind that presents the least risk.

    As to regulations it says you must place a notice if some thing is fed from two sources, it does not say it must not be done.

    I have wired 4 generators in parallel in the past and run them together, in one area we had 12, we did not have one notice about multi supplies anyone with a little sense would know that was the case. If they did not know what they were doing it was unlikely they could synchronise them anyway.
     
  16. JohnW2

    JohnW2

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    Well, for a start, the regs say that in a TN installation, one does not need to isolate neutral(s).

    However, even in a TT installation, if there is a ring fed from two MCBs (be they SP or DP) you know as well as I do that, if one is going to work on the circuit, it is 'infinitely' more important to disconnect both Ls than it is to disconnect either of the Ns - and to imply otherwise, particularly in a DIY forum is, I would say, 'not appropriate' (others may use different language).

    I don't have the regs to hand. From memory, I think it certainly does say that if something can be fed from two different 'power sources' (e.g. mains supply or standby genny), there must be a warning label - but I don't know from memory whether it could be read to mean that it would be acceptable to have one circuit fed from two OPDs in a CU/DB, provided that there was a warning label. In any event, if we were talking about a whole circuit, every single accessory/JB/whatever connected to that circuit, and 'every inch' of every cable would have to carry warning labels in order for it to be even remotely 'safe', wouldn't it?

    ... but, in any event, you surely aren't suggesting that a ring circuit in domestic premises fed from different OPDs at the two ends would be in any way 'acceptable', are you?

    Kind Regards, John
     
  17. 333rocky333

    333rocky333

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    How many cables are there in each fuseway, not sure why people are saying two rings are affected
     
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