MCB switched off but RCD still tripped

Discussion in 'Engineers' Talk' started by marlboro, May 18, 2004.

  1. marlboro

    marlboro New Member

    A bit of advice needed... I'm putting in an immersion heater timer - not the worlds trickiest of jobs, or so I thought.

    Flicked off the MCB, which is on the RCD side of my CU, and checked there was no current with the old light-up screwdriver (can you tell I'm not a spark yet!).

    Started working and the RCD tripped. Double checked I'd turned the right MCB off; double checked that the live is live with the MCB on and not with it off. Started to work again and the RCD trips again?!

    It's an old house so next job is to take up floor boards and re-trace cable to ensure that it is a direct circuit only to the immersion.

    Before I do, is there anything else that could cause the RCD to trip even though the MCB was switched off??

    Any help appreciated.

    Marly.
     
  2. marlboro

    marlboro New Member

    Doh.. Not a good start, confusing my engineers and electricians! Can't see how to delete so re-posting in Electricians forum.
     
  3. Al-Yeti

    Al-Yeti New Member

    RCD will trip becuase you havnt disconnected the Nuetral and Earth thats the side which may be cuasing it,

    remember the MCB is connected to the RED(LIVE) but the Neutral and Earth you could say are monitored by the RCD.
     
  4. phased-out

    phased-out New Member

    Hi,
    The problem you are having with you RCD is o.k. When you isolate the circuit with the MCB you are only swithing the phase.What you are finding when you cut/strip the cable your RCD will still trip. If you wish to cut/strip any cables on a RCD controlled circuit you will need to disconnect the neutral as well as isolating the live/phase. Hope this helps.
     

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