teddysnips ) gurgled happily, sounding much like
they were saying:

It's the lower master "trip" that trips - the one controlling the second
row of individual trips. These trips are labelled "Hob", "Sockets -
kitchen", "Sockets - Upstairs", "Sockets - Garage", "Sockets -
Extension", "Immersion Heater", "Cooker", "Hall/Lounge sockets
downstairs".

Given that the rate of failure is so low and MTBF so long (for
elimination purposes), and that the sub-master trip is what goes (rather
than the individual trip for the misperforming part of the system),

Silly question - it couldn't just be being overloaded, could it? What
rating's that master got, and what's the sum of the ratings below it?