Well, good question. I have an RCD-tester, but this is of the simplest type: It simply leads 30mA to earth. If the RCD trips, it's supposed to be OK. A professional will have a real meter, where you can set the test current (10mA, 30mA, 100mA, 300mA or similar) and perhaps also duration.
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I have a dedicated RCD tester, and use it in every installation that has RCD's installed,regardless of wether or not I installed them.
This sounds like a very good idea. They do fail. (I pushed the test button on one at a friends house, with no result. As it was running hot without load, I adviced him to get rid of it) Here users are advised to test them at least every six months. Reasons for this vary: Mechanical freeze, losened sensitivity or lightning damage. I don't dare to get involved in this debate...

The over-all RCD you describe is the norm here. The electric safety authority assume you use Diazed (Edison base) fuses, not breakers. These fuseboxes can only be split between two RCD:s (or no RCD vs. RCD) by sawing them apart physically. I'd love to see the look on the face of the house owner when the electrician starts sawing in the box [Linked Image] (No, I don't think it is common to do this, although legal)

[This message has been edited by C-H (edited 11-11-2002).]