Best way to find an electrical "leak"?

Discussion in 'Electrics UK' started by HDRW, 3 Aug 2012.

  1. HDRW

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    I'd been a bit worried about my electricity bill, so got one of the monitors which has a current-sensor clipped around the main Line cable to the Consumer Unit, and sends its data by radio (bluetooth?) to a display.

    Well, it's showing that I never consume less than 700W, and turning off the breakers has isolated it to the downstairs ring, and unplugging everything from that ring shows that it's not caused by anything that's plugged in!

    I've timed the meter's flashing and confirmed that it really is being consumed, not some phantom in the monitor.

    This suggests that there is leakage in the wiring itself - although 700W seems like an awful lot, and something ought to be staying warm, but I haven't found anything yet. It must be an L-N leak because the circuit is RCD protected (which tests good).

    One of the problems is that the house is full of stuff - so taking up floorboards will be a major undertaking.

    I do understand electrics/electronics (I'm a Radio Amateur, electronics has been a hobby for decades, and I learned which end of a soldering iron gets hot when I was about 8!) and I have some equipment - multimeters, and a Robin PSC/Loop meter, but I'd like advice on the best way to find where the problem is - with the minimum of disconnections, as getting to some sockets requires quite a bit of moving stuff out the way and/or climbing over things!

    The house is a 1937 3-bed Semi, with a modern Consumer Unit (fitted in 2004) and modernish sockets/switches (probably 1970s). The visible wiring at the CU is red/black PVC T&E but I suspect there may be some older wiring hidden away.

    Any suggestions? (Excluding "call an electrician", please!)

    Cheers,
    Howard
     
  2. wingcoax

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    700 watts is quite a bit, You must have missed something when unplugging.
    Either that or there is something on a connector somewhere.
     
  3. bernardgreen

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    Do you have underfloor heating ?

    Any supplies to garages or workshops.

    Any anti frost heaters
     
  4. Spark123

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    Fridge/freezer? Spur units?
    Failing that you can try to narrow it down by doing a L-N resistance test with a bog standard ohm meter and breaking down the ring into smaller legs, obviously with it dead.
     
  5. HDRW

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    Thanks for the thoughts, chaps...
    I don't *think* I missed any sockets - there aren't many in the first place (1 or 2 in each room 1930s style - the suspected 1970s rewire didn't add any, and mostly didn't even fit double sockets) but I will have another scout round just in case. "Something on a connector" - you mean a spur from a junction box? Don't think so but again I'll double-check.

    No, No, thrice No! :D

    F/F on a separate circuit, the only spur was for the front doorbell transformer, now removed.
    OK, I was wondering if there was a demon trick to this without opening up the circuit, perhaps using the Loop meter, but if not I'll have to start doing that.

    Thanks again, all!

    Cheers,
    Howard
     
  6. securespark

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    When I was trying to IR test a RF circuit, the customer insisted that everything was unplugged. She got extremely upset when I suggested perhaps there was a socket she had missed.

    "I know my own house, what are you trying to imply, that I'm going mad?"

    While I don't believe you'll be upset at all, it is quite possible you've missed something. Especially if the house is full of stuff: fused spurs and outlets may be hidden.

    BTW, I found six sockets in the back of wardrobes that the lady had forgotten were there.....

    From my 25+ years experience, the things that get forgotten are:


    built-in appliances, especially those hiding behind doors.

    cooker hoods.

    outside lighting on spurs.

    B. A. panels.

    feeds to outbuildings.

    sockets in wardrobes (!).

    stuff in lofts.

    under-floor bilge pumps.

    UFH.

    I'm sure there's a few things I've missed off, but that gives you food for thought.

    Do you have an IR tester?

    As 123 says, the least intrusive angle of attack is to split the ground floor RF circuit.

    Before doing that, you may as well just check that it is a ring to start with.

    With the supply safely disconnected, split the RFC into two by
    disconnecting the conductors at a socket on the ring, a fair distance from the board.

    Assuming the circuit is a ring, once the conductors have been separated at the board, you should have effectively two radial circuits: two lengths of cable with sockets on them.

    Then you can test each of these for resistance. An IR tester is better (although if there is a forgotten appliance on the circuit and you IR L-N, you risk frying it.... :cry: ), but if all you have is a MM, then do a test between L & N.

    With any luck, you'll find one leg good, one leg bad (sounding like Orwell now!). Then take the bad leg and break it down further. That way, you'll eventually hit the fault.
     
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  7. viewer

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    How do you get on with your neighbours? If there is a cellar/underfloor area it is possible that someone at some time has looked for a circuit under the floor, seen yours, assumed it was theirs and made a connection. If this has happened you should be able to tell if they unplug / turn off all appliances - or turn off their supply and see if anything remains live.
     
  8. ban-all-sheds

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    If this has happened disconnect it and wait for them to find out that something no longer works.
     
  9. ban-all-sheds

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    How did she react?

    Apologies and breaking out the tin of chocolate biscuits or accusing you of sneaking them in there while she wasn't looking?
     
  10. HDRW

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    Securespark,
    Thanks for your message:
    :LOL: While I could well be going mad, I have had a good hunt round, but I'll try again just in case...

    I have none of those...
    The shed is powered by a plug-in cable - unplugged for the test, no change.
    It's the downstairs ring, and I am certain nothing from that travels upstairs (the cables for upstairs go through steel conduit going up from the understairs cupboard to under the floor in the bathroom and I can account for them all)
    My brother it the one with the boat! :) And the only heating this house has is one storage heater (last switched on about 10 years ago, and turned off at the MCB) and one gas fire.
    Indeed, thanks for the help. I've been wracking my brain trying to think what I could possibly have forgotten, but no luck.

    Unfortunately not (used to be called a "Megger", I believe?). I have a PSC/Loop tester, an RCD tester, and a number of multimeters (including a really nice, calibrated Fluke). And an oscilloscope but I can't think how that would help.

    Is this where you disconnect both legs of the ring at the CU, then cross-connect opposite ends L-N, so forming a single conducting ring that runs round the sockets twice, then measure resistance L-N at each socket? This might produce an interesting map of resistances, especially if the leaking resistance is concentrated in one area. Let's see, a 700W leak at 240V (yes, I know it's called 230 nowadays, but hereabouts it's usually about 245!) would be about 2.9A, and Ohms law says that means a resistance of about 82 ohms across the pair - not sure how much the conductors' series resistance would be but I feel it would be low enough to overwhelm the 82. If it works it would save potentially breaking the ring at each socket, but I don't think it will.

    Thanks for all the advice - let's hope I don't end up in Room 101! (OK, I'm confusing two of Orwell's books :) )

    Looks like I'm in for some Front Room Mountaineering to reach the furthest socket in the ring...

    Cheers,
    Howard
     
  11. Mursal

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    Anything in the attic?

    In my limited experience, I wouldn't think almost 3A (700W) will be a fault in the circuit? Almost certainly a hidden consumer unit.
     
  12. HDRW

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    I get on very well with my neighbour (the other half of the semi-detached pair) but he's away at the moment so can't turn his power off.

    There are no cellars, just the traditional suspended wooden floor on brick plinths. To get to my wiring someone would have to drill through the party wall under the floor, and I think I'd have noticed! :)

    Interesting idea, though. Many years ago my neighbour had a supply failure, and while they were digging up the road to fix it, the contractors asked if they could take a feed from my house to his, so he'd have some power for the time they were working on it (three days, as it turned out). They connected a rather grotty bit of T&E (4mm I think) to the feed side of my meter, ran it through my house, out of a window, into his window and then presumably to his meter. It looked like the worse kind of bodge, but as they were The Electricity Board I suppose they're allowed! :)

    If I identify and disconnect the cable with the leak "blind", without taking p the floorboards, I'll ask my neighbour when he gets back if anything has stopped working. Luckily he hasn't got tropical fish, and the kitchen/fridge/freezer are on the far side of the house, so I think it'll be OK even if this turns out to be the issue.

    Cheers,
    Howard
     
  13. JohnD

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    Turn off all the power at the main switch as well as the MCB, and remove all other loads from the circuit. If you measure the resistance with a simple multimeter, you will find that the resistance between L and N is so high you can't measure it, if there is no load on the circuit.

    if the unexplained usage is on a ring, try to identify and draw the route that the ring takes. Remove a socket on each of the clockwise and the anticlockwise legs of the ring, so you interrupt the ring and any sockets between the interruptions will have no power going to them. Put the cores safely into chockblock.

    If the load now disappears, you know it is somewhere between the two interuptions.

    Interrupt the remaining part of the ring to narrow down the place where the hidden load is. And again. Eventially you will find it, or at least identify a length of hidden cable within which the fault exists. You might end up isolating that section and replacing with new cable.

    700W is as much as a small electric heater, so I will be surprised if you can't find it once you know where to look, because it will be hot, or possibly scorched and melted.
     
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  14. Chri5

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    Wouldn't have an electric towel rad would you?
     
  15. securespark

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    She reacted angrily.

    :rolleyes:

    Absolutely no apology for her behaviour.

    But then some folk are like that.
     

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