RCD tripping with no earth connected

Discussion in 'Electricians' Talk' started by Voyseygw, Sep 21, 2019.

  1. Voyseygw

    Voyseygw New Member

    I live in Spain so this is a radial circuit.

    • I have had a problem for some time with random RCD trips, so I bought an auto resettable RCD. On installing it, I set it to on and it immediately tripped I found that if I set any of my MCB’s to off I could set it to on and it would stay up. Thinking I had a cumulative earth leakage and the new RCD was more sensitive than the old one I was replacing I tested the current flowing through the earth wire at the consumer unit, this was less than 0.5 mA. The earth comes into the house and is connected to two earth wires in the house, one goes upstairs the other feeds the rest of the house. I found if I disconnected the upstairs earth wire I could get all the circuits powered up and the RCD would stay up. After a bit of fault finding I traced the earth issue to the upstairs office. The odd thing was if I plugged my UPS in and connected anything to it, it would trip the RCD the computer did not even have to be switched on! Plugging everything into the wall socket allowed the RCD to stay armed, so I suspected something wrong with my UPS. Sadly after about four hours it tripped again. Pulled the plug out of the wall in the office and then the RCD rearmed, this lasted till next morning then tripped again.
      In desperation I totally disconnected the earth from the house, my theory being that if it tripped now it can’t be an earth leakage fault. It lasted about ten hours then tripped again! I have now reconnected the original RCD at least that trips every two or three weeks not every day. What possibly can be the problem! Are there any electricians out there that can offer a explanation as to what is going on.
     
  2. Bazza

    Bazza Well-Known Member

    I despair. Why do people think that because an RCD trips the fault must be the RCD...


    That isnt going to help. There will be lots of "earthy" things connected to your house. Water and gas pipes to name but two.

    But really, if you have an earth fault in your house, that is causing an RCD to trip, then the most dangerous thing you can do is to remove the earth protection. That is the fault path to stop you from getting an elecric shock. Without it, stray faulty voltages can go nowhere and every metal device in your house that has its metal case connected to the (non) earth, and metal pipes, etc will have 230V on it.

    Put the earth back and get someone who knows what they are doing*.

    PS The only way to test an RCD is with a proper RCD tester. The person* who can do this is an electrician.
     
    sparky steve and Peterdevon like this.
  3. sparky steve

    sparky steve Active Member

    +1
    Never fails to amaze me! People never seem to realise the dangers associated working with electricity? They always seem to be avoiding employing the skills of an electrician, trying to save a few £s. Yet could ultimately pay the full price! (Losing their lives):eek:
     
  4. Tony Goddard

    Tony Goddard Active Member

    Please, please, please OP reconnect the earth (and do so with the power off, the end of that main earth wire could be hanging at mains potential!!), operating a system without it is incredibly dangerous, especially when there is clearly a fault. The RCD will be operating because another path to earth exists (ie a water pipe, structural steel etc). The only way to find the problem is with professional test gear and knowledge, get in a local spark who will sort it properly.
     
  5. Voyseygw

    Voyseygw New Member

    Yes of course I reconnected the earth back when it tripped. I was never going to leave it more than 24 hours I have a BTECH in electrical engineering so I know the risks. I live in a small village in Spain and the level of competence of the local electricians is unknown. What I need is advice as to how you diagnose this problem. I don’t do this for a living, but I am certainly happy to follow advice. I understand there is a imbalance between live and neutral of greater than 30mA. If there is a piece of test equipment that can help me find where the earth leak is please tell me. The only other earth source I have is the water pipes I don’t know how to test for an earth leak between water pipe and live and neutral. Please tell me.
     
  6. Voyseygw

    Voyseygw New Member

    Should I use a Megger between water pipe and live then water pipe and neutral, obviously with no power to the circuit.
     
  7. Tony Goddard

    Tony Goddard Active Member

    The insulation test is carried out between L & E and N & E with an insulation tester (Megger) set for 500V test, you will be looking to have north of 1 Megohm, preferably a lot more possibly off scale (usually 200 or 300 Meg, effective infinity) . The usual practice is to test all the appliances and make sure they are disconnected, then start at the beginning of the circuit, test it all, then move on, breaking the circuit by removing a socket, test again in both directions etc until you find the section with the fault.

    It sounds like yours may be an intermittent fault, which can be very, very, tricky to find as it may not be there when you test. I would start by testing the appliances you had plugged in, test both L to E and N to E.
     
  8. Voyseygw

    Voyseygw New Member

    When you say earth, you mean the alternate earth path, the water pipe. My kitchen has all the appliances built in so i’ll Isolate that part of the circuit and test the rest and hope I find the leak somewhere else.
     
  9. Voyseygw

    Voyseygw New Member

    Thinking about this further if as I proved it can’t be a leak via the circuit earth because when I disconnected the earth completely it still tripped, then the path to earth has to be possibly the water copper pipe as it is the only other earth in the house ( bottled Gad) For it to be an appliance causing the leak, wouldn’t the appliance have to have some contact with a copper water pipe. That could narrow it down to my combi boiler possible. Failing that it would have to be one of the wires in the house somehow breaking down to earth via the copper pipe, not easy to see how as all the wiring is in plastic trunking throughout all the houses in Spain mine included.
    First I’ll try a resistance test with my multimeter between live, neutral and the copper pipe if this proves negative I’ll buy a Megger and test again.
     
  10. Voyseygw

    Voyseygw New Member

    Another thought could it be that someone has bonded the copper pipe to electrical earth so that when I disconnected the electrical earth the leak was still finding a path to earth via the bonded pipe? Another test perhaps, disconnect the circuit earth and test if it is bonded to the water pipe. I know it is done in the UK but don’t know if they would do it here.
     
  11. seneca

    seneca Screwfix Select

    I know nothing at all about the Spanish wiring system but I remember someone telling me many years ago that they don't have their neutral returned to earth at the supply end? I'd be interested to hear any views on this!
     
  12. Voyseygw

    Voyseygw New Member

    I did a test of live to earth and neutral to earth this was the electrical earth, not the water pipe with a multimeter while I wait for my Megger to come from Amazon. The results were confusing, the meter ranging kept fluctuating between Megohms and Kohms the lighting circuit, kitchen circuit and sockets all did the same except the upstairs office circuit which has my UPS on it and this read a steady off the scale reading of excess of 40 Megs. I have not disconnected any of the appliances, is it a false indication because I am using a digital multimeter. I would have thought that if all those circuits were having a problem I would have registered a larger current flowing to earth when I tested for earth leakage with my ammeter, but I only register 0.5 mA earth leakage current
     
  13. Tony Goddard

    Tony Goddard Active Member

    The multimeter won't give you any usable reading as it only passes a very low voltage from it's battery to test resistance. An insulation tester has an inverter in to drive 500v through the circuit to find the leakage, the multimeter won't find a leakage unless it is more or less a dead short.
     
    Bazza likes this.
  14. Bob Rathbone

    Bob Rathbone Well-Known Member

    I have a HND in Electrical engineering, it told me nothing about electrical installation and testing them. Use the science you have gained properly and you will realize how dangerous disconnecting the earth, even for a short time, can be.
     
  15. Tony Goddard

    Tony Goddard Active Member

    I think it is best to call in the local electrician, I have no reason to doubt the basic competency of electricians in Spain, after all they have electricity just as we do here and as far as I know there is no high mortality or fire rare from electrics in Spain. The electrician, even if he is used to simpler rural installs will have a megger and know exactly what to do, I'm sure of that.
     
  16. Voyseygw

    Voyseygw New Member

    Am I missing something here with or without an earth the RCD will do what it is intended to do. If for some reason the live did touch earth the appliance would become live I agree. But if you touch the metal case, you would provide an earth and current would flow to earth but if the current exceeded 30 mA the RCD would still detect an imbalance between live and neutral and trip. It won’t detect a leakage but will still save your life, or am I wrong?
     
  17. Bazza

    Bazza Well-Known Member

    @Voyseygw keep an eye on your expenditure. An (unnecessary) new RCD plus the cost of a Megger must equal the cost of an electrician to sort this for you.
    You might need an RCD tester too…

    Edit. An RCD might save your bacon, but RCDs are only a supplementary way of providing safety. They are never used as the primary safety method. We use other basic protection, such as ADoS to provide that.
    And you haven’t tested your RCD.
     

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