rcd and mcb tripping straight away

Discussion in 'Electricians' Talk' started by number 1, Nov 25, 2010.

  1. number 1

    number 1 New Member

    Hi i have been asked a question from a friend  why her sockets (1 mcb 32amp supplying all sockets in house excluding kitchen) are tripping out instantly also taking out the  80a rcd. her husband is a ex spark but is now too old to play around but he has checked the neutral/earth in the cu and they are on the right bars. he has also checked every socket fro loose /short circuits all seem fine. even when nothing is plugged in to any socket it still trips instantly... i have called round and  put a new mcb in and it still trips, i have split the ring in what i think would be the mid way point and it still trips. is there anyway in finding this quick before i have to disconnect all sockets one at a time till i find where it stays on. ? i have no test instruments by the way except for a basic multi meter and test lamps.

  2. sinewave

    sinewave Screwfix Select

    New MCB indeed!

    You'd better change your username from 'Number 1' then if U aint even got any test Gear!

    You need some for this job if U want to make any headway.

    Megger the cores first with an Insulation Tester would be a start!
  3. number 1

    number 1 New Member

    i aint a spark, the number 1 isnt related to as you can guess. ha ha
  4. Bazza-spark

    Bazza-spark Screwfix Select

    Hi number 1

    You could try testing with your multimeter betwen live and earth, neutral and earth and live and neutral to see what readings you get.  If the breakers are going out straight away the fault may be easy enough to find.  Make sure you have nothing plugged in when testing or you will get false readings especially between neutral and earth and be sure you isolate the circuit before you start.

    If you can find a low reading then you can start breaking the circuit down into sectons to see which section the problem is on.  Has anything been done such as putting up units, curtains, shelves or anything that could have caused a screw or nail through a cable?

    Kind regards

  5. number 1

    number 1 New Member

    no, no work has been done it just suddenly tripped and hasnt been able to reset ever since.i will carry out the test Sat and get back to you. cheers BS
  6. jamie1981

    jamie1981 New Member

    you need to check insulation readings to make sure there is no fault. Also if it is a spilt load consumer with 2 rcds you need to check that someone has not pinched a neutral from the socket circuit to feed another circuit on the oposite rcd .

  7. diymostthings

    diymostthings Well-Known Member

    What type of supply do you have? - TN-S, TN-C, TN -C-S ? If PME then neutral to earth readings will be meaningless in this instance. Are you sure nothing is plugged in? What about hidden fused spur outlets (e.g. to an immesrion heater)?

  8. spinlondon

    spinlondon Screwfix Select

    Has someone recently hung a picture?
    I once came across a situation where a carpet gripper was nailed through some T&E, only ever tripped if someone stepped in the wrong place in the room.
  9. pearcy

    pearcy New Member

    RODENTS..................YUM ....YUM..PVC
  10. unphased

    unphased Screwfix Select

    Without going in to technical jargon this fault is a direct short. Simple. Without putting the cart before the horse and testing all the circuit find out from the woman what was the last thing she did before the event started. A direct short in a cable does not just suddenly "happen", something causes it and a nail through the cable as mentioned is primary suspect IMHO.  Hanging Christmas decorations were we?
  11. Mr P

    Mr P Guest

  12. wally

    wally Screwfix Select

    Sounds like you will need to disconnect the circuit & carry out insulation tests as said previously otherwise you will get nowhere.   It could even be in the socket faceplate itself, had one last week, after disconnecting it the socket had a zero reading to earth.      Had to replace 3 sockets a few years ago in a kitchen, had to change them 3 times actually over a period of time where the sockets were at fault.    The problem was eventually solved, the lady caught one of her cats weeing on them.  Not sure what happened to the cat.
  13. unphased

    unphased Screwfix Select

    The cat problem would come under the WEEE regulations. ;)

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