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Protection Riddle No.42 - Spasmodic tripping on the RCD
Have a property in Spain with spasmodic tripping on the RCD.  I have found a neutral to earth fault with a voltage reading of 378 volts!,  there is no cross bonding in the houses over here and all the earth wires are in connector blocks throughout the house.  I cannot find where the earth stake is and so don´t even know if an earth wire is connected to it. I have had this problem in other houses and after doing many re-connections of the earth wire managed to get the voltage down to 5 volts N - E.  The only test equipment I have out here is a Fluke Multimeter and an Avo.  It is not possible in this part of Spain to buy any other equipment.  Any ideas on this problem would be very much appreciated.
Author : Brian Thurlborn - From: Spain
Mon, August 3rd, 2009 - 20:11
I cannot understand your mean when you say about neutral to earth fault voltage equal to 348 volt, however my first guess about your problem is neutral wire cutting or disconnecting. Please note to below figure, when disconnection of neutral occurs in system, you face to phase voltage between neutral and earth via load impedance. Also the RCD relay can operate due to capacitate leakage which is created through stray capacitance in this case.

Author : Hamid - From: Iran
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