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Rcbo white lead

Does anyone know the circuit arrangement for these loss of neutral protection leads?
  • In a TN-C-S system the C.P.C.s of the final circuits connect to the earth bar in the consumer unit. The white R.C.B.O. leads connect to the earth bar. Neutral and earth are connected together at the cut-out. If the neutral is lost so is the  earth connection (P.E.N. broken). 


    Z.
  • On PME it is not a lot of use, I agree, but oranges are not the only fruit, and many places are not TNC-s.


    The design I have seen somewhere showed  a six diode bridge,  (like this 3 phase example  here )  albeit with series resistance to two of the lines - so the 3 wires are not connected to each other, except by back to back diodes, but voltage between any two would create some  DC to keep the circuits alive. In normal use the diodes on the FE path are not needed, as they do the same as the ones on neutral, and the circuit collapses to a normal 4 diode bridge  here.

  • Zoomup:

    In a TN-C-S system the C.P.C.s of the final circuits connect to the earth bar in the consumer unit. The white R.C.B.O. leads connect to the earth bar. Neutral and earth are connected together at the cut-out. If the neutral is lost so is the  earth connection (P.E.N. broken). 


    Z.




    Well, if you are inside a TN-C-S system I suppose loss of neutral also means loss of earth and thus no hazard. If protective bonding is in place then the white lead will continue to do its job.

  • It depends on which side of the PME N-E link in the suppliers head the neutral break is.


    If it’s on the suppliers side everything that is earthed within the installation will be liven up to the best part of the mains voltage.


    Should the RCD earth connection detect the reduced voltage difference between line and earth? I don’t think it will.


     Andy Betteridge 


  • Certainly makes a klaxon and strobe wiried accross the MET and an earth rod metres away start to look attractive. Better still that loss of PEN detectctor featured here a few years back (although prohibited) has its merits as does the old voltage operated breaker RCD type thingy!