Dave Plowman (News) wrote:

Two 3 Kw kettles on the same extension should have blown the plug fuse and
quickly.

A 13A fuse is required to carry 1.6x the rated current without blowing,
and only required to blow within 30 minutes for 1.9x rated current, so
whether, or how quickly it should blow, depends on the duty cycle of the
two kettles ...