The Curious Incident of the Plug in the Nightime [longish]

Discussion in 'UK Motorcycles' started by sweller, Dec 1, 2004.

  1. sweller

    sweller Guest

    Yesterday evening I was finishing off fitting a ring main in the loft
    (it's complicated as to why) and had got to the cutting the 15A feed to
    the immersion heater which I was going to divert for my purposes stage.

    After satisfying myself that I had the correct feed by (a) pulling the
    cable and my glamorous assistant confirming that yes it was the one that
    went to the heater switch and (b) that the breaker was tripped and the
    heater no longer worked.

    Out with the cutters; in position (inches from an open loft hatch); start
    to snip; BANG goes the main RCD and out go the lights. Perhaps it wasn't
    the right one after all.

    I have a cheapy power in a cable type beeping detector which I was
    convinced didn't work because it saw electricity "everywhere".

    Using this coupled with a process of elimination (tripping in, one at a
    time, each circuit in turn) it appeared that cable was live when both
    the Immersion heater and upstairs lights breakers were made.

    WTF?

    A trip to the lockup to get my meter (which I should have used in the
    first place) it shows 240v at the Immersion heater feed but with only the
    lights breaker made; 17v.

    Working with the 'live' 17v end I didn't feel anything but touching the
    ends whilst wiring in the junction box caused the RCD to trip, again.

    The conclusion? Induction from where all the lighting cables and feeds
    to the airing cupboard (+CH pump) go through a single hole in the joist.

    http://www.sweller.dynalias.org/images/joist.jpg [phone picture alert]

    I carried on and the ring main works as does everything else - working on
    the theory it hasn't caught fire so it should be ok - it's ok.

    Thoughts, opinions?
     
    sweller, Dec 1, 2004
    #1
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  2. sweller

    platypus Guest

    platypus, Dec 1, 2004
    #2
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  3. sweller

    Greybeard Guest

    Seems like a faulty earth somewhere.
    If the earths are all fully ground, i.e at equal potential (and on a PME
    that can well be 17V above earth) then you shouldn't have a had a problem.
    If, on the other hand, you measure between earth and neutral and you have a
    potential difference, then you have a _serious_ earth fault, and on a PME
    system, this could be very dangerous.
    Assuming you are on PME, make sure all the crossbonding between the water
    and gas pipes in the house are secure and route correctly back the earth
    block. Check all connections are tight, and no serious corrosion is evident.

    I'm sure it will be down to earthing, but it could be a badly wired
    appliance or fitting, allowing a back flow of electricity when not actually
    switched on.

    The kitchen lights should not be on the same circuit as the immersion. That
    needs to be investigated to be truly safe. The kitchen lights ideally should
    be fused at 5 amp (6 amp if a breaker) and the immersion fused at 15. The
    ring main should be tied into the upstairs ring main as it is capable of
    drawing 30 amps. Hence you made it a ring main! Had it been a spur, you
    could have got away with taking 1 or 2 extra sockets attached to the
    immersion circuit, so long as the combined load exceedeth not 15 amps. But
    remember, when the immersion is on, it is pulling around 13 amps on it's
    own.

    HTH, Just my 2p worth, and things may have changed a little since me being a
    sparks, but the fundamentals will still be the same.
     
    Greybeard, Dec 1, 2004
    #3
  4. sweller

    Ace Guest

    On Wed, 1 Dec 2004 10:36:17 +0000 (UTC), Keelworm

    No need to quote it in full, though. Learn to snip, newbie.
     
    Ace, Dec 1, 2004
    #4
  5. sweller

    wessie Guest

    sweller emerged from their own little world to say
    http://www.niceic.org.uk/partp/building_regs.html
     
    wessie, Dec 1, 2004
    #5
  6. Andy Broadhurst, Dec 1, 2004
    #6
  7. sweller

    Christofire Guest

    Are you sure it wasn't the 27 4-ways that you had running from it?
     
    Christofire, Dec 1, 2004
    #7
  8. sweller

    Greybeard Guest

    That sure will be a long month!
     
    Greybeard, Dec 1, 2004
    #8
  9. sweller

    sweller Guest

    The wiring in the house is fairly recent and all the earth bonds on the
    water pipes, and there's plenty of them, appear to be clean and tight

    They're not.

    Hacking into the upstairs ring main would have involved lifting carpets
    and floorboards. Easier to divert the immersion feed that isn't used to
    feed two computers.

    The immersion has been disconnected and its 15A feed diverted to the loft.

    It does, I think I'll get the earths checked checked. Although they've
    never given me a problem before. We've been in the house for 5 years.
     
    sweller, Dec 1, 2004
    #9
  10. sweller

    Greybeard Guest

    Probably re-wired before split systems came about.
     
    Greybeard, Dec 1, 2004
    #10
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