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Fused connection unit burnt out

Discussion in 'Electrics UK' started by Kerryw92, 13 Aug 2019.

  1. Kerryw92

    Kerryw92

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    Hi,

    Just a quick one, I'm sure I'll be asking more at some point as I just purchased my own home finally!

    Anyway, house is a new build, been here two years now.

    In the kitchen there is a fused connection unit that goes to a twin socket that powers the washing machine & dishwasher.

    Today said FCU failed, initially thought it was simply the fuse so went to replace. At this point I realised it was clearly worst as the fuse tray would not budge, a lot of force later and it popped out and I found the damage.

    Fuse itself is fine despite the outside edge being burnt, the housing itself is melted around the live terminal, most if not all of the contact is gone.

    Question I have is, the house is under warranty and the electrician has been out. He's saying the cause was running both appliances at the same time.

    Am I correct in thinking surely if this was the issue the 13a fuse should have blown and not have the switch melt instead.

    Tested the fuse in a lamp, it still works.

    When this happened the rcd in the fuse board also didn't trip.

    I'm guessing when installed the wires simply were not done tight and it's been arcing the last two years. The washing machine is close by and does rattle everything a lot so I guess this would not have helped.

    Next step is checking all the sockets as I identified one last year with a similar issue when I noticed the housing didn't go flush with the wall.

    Thanks
     
  2. EFLImpudence

    EFLImpudence

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    I think you have analysed the situation perfectly. Loose live terminal.

    Just say - RCDs do not react to such a situation.
     
  3. Kerryw92

    Kerryw92

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    Cheers, assumed the rcd would have tripped but I'm yet to research into the workings of them properly. Only experience I usually get of them is resetting them in work when the spot lights draw too much power first powering on and trip it haha.
     
  4. EFLImpudence

    EFLImpudence

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    RCDs only react to earth-leakage by any path - i.e. they detect an imbalance between the Line(live) and Neutral conductors, 'missing' current in the Neutral conductor.
     
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  5. Risteard

    Risteard

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    Should that not be line and neutral (live) conductors? Neutral is every bit as much a live conductor as a line conductor is.
     
  6. flameport

    flameport

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    Almost.

    Having two high power items on a single 13A fuse will cause moderate overloading, and that will result in the fuse and fuseholder being significantly hotter than it would with just a single item connected.
    A 13A fuse doesn't blow at 13A - typically it will take 20+ amps for an extended length of time.

    The fault is the poor design - a single 13A FCU for the two appliances. Depending on the circuit, it may be possible to change the FCU to a 20A switch.
     
  7. EFLImpudence

    EFLImpudence

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    Technically - but I was 'translating' Line for the OP in case he did not know what it meant.

    I often do that.
     
  8. Kerryw92

    Kerryw92

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    Ah thank you for this, I'll have a look into it. Always assumed as this socket was put in place for these appliances specifically it would have been up to scratch as surely they would expect both to be on at some point.

    Worst case scenario is I can run another circuit anyway if the issue re occurs and have both on a separate FCU. Consumer unit is just above so wouldn't be hard to run another feed down & 4 spare breaker slots available. Need to add another socket into the kitchen anyway to move the chest freezer so I'll look at doing it both at once.

    With regards to line, live, neutral etc I must admit I'm not entirely clued up on the names of everything. Usually work on cars and it's simply positive and earth I have to deal with.
     
  9. flameport

    flameport

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    If it's like most new builds, the only consideration in the design of anything was to get the lowest possible price, and then find ways to reduce that price even further.
     
  10. Harry Bloomfield

    Harry Bloomfield

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    I would be asking why there is a twin 13amp wired via a FCU at all, why it is not wired on a ring and able to sustain the current demand you would expect.

    As others have said, the RCD would not trip for that sort of issue, nor would the FCU's 13amp fuse blow if the overload was on brief. Poor connections to the FCU or the 13amp fuse carrier would cause the damage, the damage could also have been caused by heat from the fuse carrying more current than it was designed for.

    I also query why you would not expect to be able to run both appliances at the same time, it is an absoutely ridiculous claim for the electrician to make. From memory, a twin 13amp socket is designed to supply a maximum load across both sockets of 20amps (not the 26amps you might expect), but both appliances running at the same time would not exceed that limit.

    Throw it back at the electrician to repair and also ask why the socket is supplied via an FCU at all.
     
  11. Kerryw92

    Kerryw92

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    If I'm honest the whole install is questionable.

    The central heating and cooker run on the same circuit for some reason.

    I changed the bayonet fitting in the downstairs hallway last week as I had enough of it fouling on the front door every time it was opened to a flush fit and found that it and the kitchen lights have been wired into the upstairs lighting circuit and not the downstairs one.
     
  12. Harry Bloomfield

    Harry Bloomfield

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    It sounds as if you ought to be getting and paying for an independent electrical inspection, so you can see the builder's electrician in court.
     
    Last edited: 13 Aug 2019
  13. winston1

    winston1

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    Not conventional, but why should it be a problem?
     
  14. winston1

    winston1

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    You don't need an FCU, the appliance plugs have fuses.

    Running new circuits is notifiable work.
     
  15. Harry Bloomfield

    Harry Bloomfield

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    Just a thought - Is the twin socket below a worktop and the FCU above it and able to be used as an isolator?
     
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