No need to wait - my experiment 2 is now done.Usually powerbreaker, I may be able too try one during the week
You're right about the Powerbreaker. I've just tried with a Powerbreaker H22. As you say, it won't reset without an earth connection. Furthermore, if one disconnects the earth whilst it is 'on', it immediately trips. It's therefore impossible to ascertain whether or not the test button is 'testing to earth' but, for what it's worth, when one does have an earth connection, the test button works as expected, and does not take out the upstream (also 30mA) RCD.
Kind Regards, John