srnet:
Why would anyone install a 300mA RCD ?My shed, built by me, was wired to the then current UK 'regulations' (not actually legal requirements) which specified 30mA RCDs. That was maybe 20 years ago.
Maybe a "repossessed" one from an industrial site/employer in the mistaken belief that they were enhancing their home safety. That said, the original poster did state the RCDs in question were 100mA and 300mA.