Residual Current Device (I∆n = 650 mA)

only on a programmable earth fault relay not a fixed RCD or anything like that. It's not a value I'd expect anyone to normally need. 30mA, 100mA 300mA and then multiples of half amps are the go-to values, and I'd not trust it to discriminate with half an amp or an amp.
In my experience,   admittedly limited to  earth fault discrimination between layers of distribution and final circuits, correctly isolating the minimum area with a fault is better done with time nested delays, rather than by increasing fault levels.
Mike

Yes fully adjustable shunt trips on an MCCB with earth fault protection up to 30A and an adjustable delay time.

JP

The only reason I ask is that the Megger MFT X-1 Multifunction Tester has RCD test I∆n settings of 10 mA / 30 mA / 100 mA / 300 mA / 500 mA / 650 mA / 1000 mA.

These are fixed settings, distinct from the Variable RCD (VAR) function that can be set to any I∆n between 10 mA and 990 mA.

I've never seen an RCD with an I∆n of 650 mA before and a quick search of typical manufactuer's catalogues online causes me to further doubt their existence.

Can anyone shed any light?  

- Ross

Well, 300 mA is approximately 1/3 A and 650 mA, 2/3 A.

Renard preferred number?