KYORITSU 5406A - Manual (Page 13)

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There is also another kind of RCD called "Type B", for which tripping is
ensured for residual sinusoidal alternating currents (like type AC) and
residual pulsating DC currents (like type A) and pure or nearly pure DC
current, whether suddenly applied or slowly rising. It is also very rarely used
in practice because these are only a few models on the market and the price
at the moment is very high.
Tripping current I⊿ is the lowest residual current which can still cause
tripping out RCD.
The RCD tester Model 5406A starts to drive test current from 20% of I⊿n
and then increases it until RCD trips or up to 110% of I⊿n.
This test is normally named Auto ramp test and it can be used to confirm the
real sensibility of the RCD.
If RCD trips before the 50% of its I⊿n, there could be a certain leakage or
fault current that is already flowing to the ground, or the RCD could be out of
characteristics.
In order to check the leakage or fault currents there are specific leakage
clamp meters as Model 2432, Model 2433, Model 2413F, Model 2417.
The RCD tester Model 5406A can test the Trip out time t⊿ and the Tripping
current I⊿.