RCD tripping in Consumer Unit

JohnW2 said:

Hence, for, say, 50m of cable that would be 5,000 pF (5 nF) - so, about 640 kΩ at 50 Hz, resulting in an L-E 'leakage' current of about 0.36mA at 230V. Since the N-E potential difference will usually be fairly negligible, the N-E leakage current (which will reduce the L-N imbalance) is also likely to be fairly negligible but, in any event, the maximum L-N imbalance would be about 0.36 mA for 50m of T+E.

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If I understand correctly that is not correct; the N-E leakage will add to the total leakage.

EFLImpudence said:

If I understand correctly that is not correct; the N-E leakage will add to the total leakage.

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Yes, you're right - my apologies. The L-E leakage (through cable capacitance) will add to the L current (as seen by the RCD), whereas the N-E leakage (through cable capacitance) will subtract from the N current (as seen by RCD), so the L-N imbalance seen by the RCD will be the sum of those two leakages.

However, that makes very little difference to the bottom line of what I said - since, as I said (and as Mr Ohm would confirm), the N-E leakage (current) will be 'fairly negligible', since the N-E potential difference will also usually be 'fairly negligible' - so the L-N imbalance seen by the RCD will primarily be that due to the (much larger) L-E leakage.

Kind Regards, John

JohnW2 said:

I obviously can't speak for others but, probably because all of my meters (including the 'fairly expensive' ones) are pretty (in some cases very!) old, I don't have any which can measure AC currents in the mA range.

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Even my older ones (I am pretty sure) will cover that range.

EFLImpudence said:

If I understand correctly that is not correct; the N-E leakage will add to the total leakage.

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L-E leakage will add to the total, N-E will subtract from that total...

[EDIT] As your were - it is a duplicate of John's post, sorry..

Harry Bloomfield said:

Even my older ones (I am pretty sure) will cover that range.

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Fair enough. A good few of mine don't do AC current at all, and those which do generally to not have mA resolution.

Kind Regards, John

My AVO Mk8 will measure mA, but would not measure the difference between two power cables, need a clamp on meter for that.

As to measuring actually mA to earth, this is why the ELCB-v was a failure, there are likely many paths to true earth.