Why does backup sometimes fall in the profit test when an RCD is triggered?
If a load with an inductance is connected to an RCD, it generates a reverse voltage when switched off,
which can become very large.
The profit test is protected by surge arresters, which allow current to flow in the event of an overvoltage. With larger inductance, the current can become so high that the fuse of the Profitest triggers.
It is best to turn off all loads before performing a trip test.