You can often get a resistance reading from the test resistor, it is just he has had it wired incorrectly and the resistors are often not rated large enough for constant use - usually <40ms @ 240v!
I'm not sure on what 100A through the torroidal transformer will do to the gubbins of the RCD tho.
I'm not sure on what 100A through the torroidal transformer will do to the gubbins of the RCD tho.
