Does the Megger MFT RCD test mimic an electric shock

[JohnW2]

You do not need to unscrew the busbar from the RCD and all the MCBs; switching off the MCBs will disconnect the circuits.

Very true! However, that does not alter the fact that, unless one is certain that there are no N-E faults, one needs to disconnect the load side of the RCD from the neutral bar (which involves 'unscrewing a screw')

Kind Regards, John

 

[EFLImpudence]

Very true! However, that does not alter the fact that, unless one is certain that there are no N-E faults, one needs to disconnect the load side of the RCD from the neutral bar (which involves 'unscrewing a screw')

Yes, I have throughout said the load side conductors should be "disconnected" when testing an RCD - either by the hazardous task of unscrewing - and by opening switches.

 

[JohnW2]

Yes, I have throughout said the load side conductors should be "disconnected" when testing an RCD - either by the hazardous task of unscrewing - and by opening switches.

Indeed, and I have been saying essentially the same - but I did allow me to get confused by Jupiter's reference to 'disconnecting fromthe busbar - which as you say, is never needed, since switching off all the MCBs achieves the same.

I've also possibly introduced some confusion because I was at one stage in the discussion talking about eric's suggestion of testing an RCD 'with all loads connected'. As I said, that sounded (to me) to be a bad idea, because it could result in the 'passing' of an RCD which was actually faulty, in the 'dangerous' direction - i.e. because, tested in isolation, it would would have required more than 30mA to trip it.

Moving away from eric's suggestion, I have said that, if one has switched off all the RCDs, there is theoretically no need to disconnect the load-side neutral of the RCD if one is 'certain' (e.g. from IR testing) that there is no N-E fault. However, even if one doesn't have that certainty (e.g. have not done IR testing) but nevertheless leaves the neutral connected, that could not result in an incorrect result in the 'dangerous' direction (i.e. 'passing' an RCD which, if tested in isolation, would require >30mA to trip it) - the 'worst' possible erroneous result being that one might 'pass' an RCD which would, alone, trip with less than 15mA residual current (which isn't really a 'safety' concern).

Kind Regards, John