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I absolutely agree. Safety first.

But during development and repair in a laboratory .. sometimes there is no other option.

For example: How useful is a current clamp ... while the DUT can not be switched ON because it immediately trips the RCD?

The resitor has two jobs:

* to limit the current in a way the RCD does not trip

* to give a voltage that can be measured with a scope.

What value of resistor to use .. will depend. Is it too low: the RCD still will trip. Is it too high, the mesurement may be useless.

If the current is too high for the 100R .. then one may use a higher value resisitor .. but one needs to consider power dissipation.

In the end: cutting the EARTH wire permanently is a no go.

The person in the laboratory needs to be aware of the risks.

Klaus