The problem with AC RCDs is that they have no defined response to d.c. currents at all - the standard simply doesn't mention anything on the subject - so there's no generic safe level. Individual devices well well be safe - if a 30mA normally trips at say 24mA you might imagine that even with 6mA of d.c. bias it should still trip at 30mA - but of course individual devices can vary, and a ramp test only tells you how it responds in one set of circumstances - test on another day of the week, at a different ambient temperature, or with a slightly different variation in supply voltage, the result may well be different - as long as it trips by 30mA it would be compliant, and you'd have no margin at all. There was even a rumour a few years ago that RCDs supplied into the UK market labelled as AC types were really A types under the hood (to simplify manufacturing as other countries were demanding A types, while meeting UK expectations for AC types). I guess the least worst option is to ask the manufacturer of the particular device concerned - as they may be able to define d.c. performance that's above and beyond the BS EN.

  - Andy.

Or if you have a tester that can create a test with the lumpy DC (unsmoothed rectified) superimposed that an A type should respond to, there is no harm in seeing what that specific RCD does to either set your nerves jangling or give a warm feeling.

And you could consider how serious is it if that RCD is blinded - if the whole site loses RCD all cover, including all the sockets, then it is more serious matter  than if a only lighting circuit that until a few years ago would not have needed an RCD anyway is affected.

There are not that many credible failure modes of LED lights or induction hobs that actually would trip a type A and not a type AC it needs a fault to earth after the rectifiers that does not actually blow the diodes to smithereens or open a series fusible resistor or similar weak link. Possible, but rare.

Or if you have a tester that can create a test with the lumpy DC (unsmoothed rectified) superimposed that an A type should respond to, there is no harm in seeing what that specific RCD does to either set your nerves jangling or give a warm feeling.

And you could consider how serious is it if that RCD is blinded - if the whole site loses RCD all cover, including all the sockets, then it is more serious matter  than if a only lighting circuit that until a few years ago would not have needed an RCD anyway is affected.

There are not that many credible failure modes of LED lights or induction hobs that actually would trip a type A and not a type AC it needs a fault to earth after the rectifiers that does not actually blow the diodes to smithereens or open a series fusible resistor or similar weak link. Possible, but rare.