So, that is THE threshold.
No - it's the maximum threshold required by the standard.
It does not have a trip threshold less than that; the threshold is still 30mA.
No, a device can have a threshold different to the one required by the standard, as long as it is different in the right direction and the standard only requires a minimum, or maximum, threshold.
That it trips at less than the threshold does not alter that required threshold.
Indeed it does not, but it does "alter" the threshold for operation of that particular device.
In terms of the normal use of language, I don't think one normally can.
I suppose that one could have a situation in which one was free to choose a 'threshold of choice', but within certain specified limits.
Similarly, I suppose that one could talk of a 'threshold' between the residual currents at which an RCD would be tripped or non-tripped - which would not be a fixed current (but, rather, anything in the range 15-30mA) - but we don't say things like that.
Kind Regards, John
IMO all of us, you, me, EFLI, Schneider, are being a bit sloppy, or at least elastic, with our use of "threshold".
Let's remember that a threshold is actually a physical barrier across the bottom of a doorway into a building or room which is there to stop the thresh used as a floor covering from escaping, i.e. to hold it in place in the room.
Regulations or standards can require a device to have a maximum (or minimum) threshold, the crossing of which causes it to do something. IHNI if the requirements for RCDs specify minima, but if they don't then one which tripped after an imbalance of a microamp was sustained for a microsecond would comply with the requirements for the 30mA device we all know and love. Its threshold would be way below the maximum required, but the fact that it was would not change the fact that the standard specified a threshold, nor that the device had a different one. (Although I suspect that such a device would not be well loved.)
I think we do all know what Schneider are trying to say, and it does make sense - the device will flag a problem if a PD between true earth and installation earth exceeds X volts, where X is to some extent indeterminate, but which they say will never exceed 35V.
It's threshold, i.e. the line which it recognises has been crossed is variable, and will vary from minute to minute, I expect, and will be influenced by any number of external factors, but what they are saying is that at any given point in space-time it will have a threshold which is < 35V.