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WTH is the BFD? Your communication is NFG. Have you considered a GF?

Don't be so narrow minded. All of the acronyms he used are legitimate for countries other than the US. Just because they mean nothing to you doesn't mean you should mock him.

RCBO = Residual Current Circuit Breaker with Overcurrent Protection: this is essentially the same as a Ground Fault Circuit Breaker. Residual Current is a form of Ground Faul detection, as opposed to Zero Sequence. Here in the US we don't use ZSGFP unless you have a resistance grounded system, which is never the case in residential applications, so we don't bother with the distinction and call everything "Ground Fault".

TT system; In other countries, they have a nicely defined way of describing the way their power delivery is connected to earth (ground), spelled out in International standard IEC 60364 as three families of earthing arrangements, using the two-letter codes TN, TT, and IT.

The first letter indicates the connection between earth and the power-supply equipment (generator or transformer):

The second letter indicates the connection between earth and the electrical device being supplied:

RCD = Residual Current Device; This is a Ground Fault device that is external to a circuit breaker, in other words, like a GFCI receptacle, except wired to the circuit breaker to trip it (using a Shunt Trip).

MCB = Miniature Circuit Breaker. These are essentially the equivalent of our residential circuit breakers, as opposed to MCCBs, which are Molded Case Circuit Breakers, although here in the US, residential CBs are still Molded Case.

OK, class dismissed.

JReaf,

You said it right. These are commonly used so most of us understand it.

Isolate the house from the mains and start measuring for ohms between neutral and earth on each of the RCBO circuits; they should all present v.high resistance. One that isn't indicates a fault that needs to be rectified before the installation will work properly.

Check that all of the RCBO circuits' neutral conductors are wired downstream of each RCBO and not connected inadvertently directly to the common neutral bar upstream of them.

After that, report back here with the findings. _{<Subscribes to discussion>}

Thanks Pwslack, for the suggestions. Actually the type of Rcbos I used are the Merlin Gerin C60H. And I made sure that the Blue/neutral supply lead from the Rcbo is connected to the neutral terminal block and load neutral is connected to the out going terminal of the Rcbo.

OK.

And the circuit neutral-to-earth resistance values?