On 08/02/2019 17:00, John Rumm wrote:

Having said that there are no guarantees, ISTR Adam mentioning a case
where an appliance fault took out the main incomer fuse, leaving its
plug fuse un-blown and the circuit MCB un-tripped!



You are close John.

Two cases where this sort of thing has happened.

1. 1970s bungalow. Tried to slacken off the cooker switch from the back
box and the live cable fell out the terminal and shorted to earth. This
took out the house fuse but left the 30A fuse wire intact. I'll put that
down to an old fuse.

2. Flats with a 16mm T&E submain supply to each flat. A fault[1] on the
lighting circuit took out the 6A lighting MCB and the 63A head end MCB.
In this case there was no 10mm extra earth cable from the head end to
the flat as no supplementary bonding was needed (no gas and a plastic
water supply) and it would be very similar to the OPs set up. The 80A
BS1361 fuse in the suppliers cut out was OK.

[1] It was LE short in a new light fitting the tenant had fitted.

--
Adam