The RCD functions normally, by sensing that the line and neutral currents
flowing through the unit are balanced, any leaking current flowing to earth
resulting from deterioration of the insulation values downstream of the
unit, will be detected and summated. (upstream faults can also cause an RCD
to trip; but these are peculiar to the type of supply on the premises, I
would ignore these at this time, since the arguments are complex).
Ideally an competent electrician with an RCD tester may determine if the RCD
is OK, particularly the so called ramp test; but if the problem appears to
have gone - albeit temporarily, this test won't be conclusive. An RCD
although rated at 30mA on the box, can trip at much lower values.
The tripping mA's are additive for each leaky item - these are usually
appliances with heating elements or have condensation/moisture around -
freezers, refrigerators, washing machines, tumble driers, dishwashers,
convection/microwave ovens, kettles and grills; but the notorious one is the
iron, where fluff collects in the internals of the iron, around the heating
Another test, which can be carried out, is specifically that for portable
appliances - P.A.T.; but this also requires a special tester used by a
I don't know what circuits your RCD is protecting; the regulations basically
require these for socket outlets which potentially be used outdoors, this
could include a cooker but this is only required if there is socket outlet
on the cooker unit - these have elements also!. Some electricians fit
showers to these, as the manufacturers usually recommend this; but this is
not required to the regulations.
If there is a recurrence, I would unplug all your appliances with an earth
connection to them, check for moisture around the connections where
possible; and plug them in one at a time. You may be fortunate and find an
appliance problem; but it could also be that the RCD itself is faulty.
Ideally of course, a competent electrician with the proper testers may be
able to isolate the problem; but these faults can be difficult and time
consuming to find.
Usually I find that the RCD is operating correctly due to a faulty item; (or