Assuming you have *working* 30mA RCD protection for the socket final
circuit, you do not need a plug-in RCD adapter.
I say working because they can fail - without you knowing.
- Remain "on" - but fail to operate even by test-button (MK, Wylex)
- Remain "on" - but fail to operate within spec, but do operate by
test-button (MK, MG, Crabtree)
- Stay "off" - complete failure and refusal to turn back on (some
This is extremely rare - however it does happen.
- Test the RCD/RCBO regularly via the test-button
- Never drop any plug-in or in-line RCD, they are fragile mechanical
RCD can drift out of specification due to stiction alone hence the
need for regular operation, rough handling can also cause problems.
In some circumstances it is worth using 110V power tools & transformer
Example would be up a ladder (30mA will throw you off).
I you ever use 240V anywhere damp (pumps, mowing) then you may want to
keep your extra plug-in RCD.