[minor edit i typed zoning when i meant installation method]
um no sockets aren't the only 0.4 sec thing
and sockets don't always have to be 0.4 sec (though the alternative is going to be a hell of a lot more trouble to ensure)
(from a usefull summary document i found called cableselection_web.pdf note: this document while seeming generally fine uses a very pessimistic interpretation of the installation method rules)
‘high’ risk circuits These are circuits for which the shortest disconnection time must
always be maintained: 0.4 seconds. According to the IEE Wiring Regulations,
this category consists of fixed bathroom equipment (shower pumps, electric
heaters), outdoor and garden mains socket outlets, and other places where the
users are likely to be exposed to wet conditions. It is assumed that exposure even
to the full supply voltage is not likely to be dangerous if it is restricted to 0.4
seconds. Other high-risk areas are recognized by the Regulations, but these are
unlikely to be found in the home (the possible exception is a swimming pool, if
you’re fortunate enough to have one).
It is commonly thought that domestic kitchens are a ‘high risk’ area, and are
therefore regulated in the same way as bathrooms; this is, in fact, not true (at least
according to the IEE Wiring Regulations). If you wish to protect your kitchen
more strictly than other parts of the house, this is sensible, but not a regulatory
issue.
‘medium’ risk circuits These are all circuits supplying socket outlets and hand-held
appliances. These circuits also require disconnection times less than 0.4 seconds,
unless the maximum shock voltage is less than 50V. It is assumed that an
exposure to 50V is unlikely to be dangerous, even for an extended time. In fact,
a person with clean, dry skin standing on a dry floor can tolerate much higher
voltages that this. The 50V limit includes a safety margin to account for damp
skin. These circuits must disconnect within 5 seconds; this time is really rather
arbitrary, but there has to be some sort of limit. In practice, if the shock voltage
is less than 50 V, the disconnection time will be adequate anyway, as will be
discussed.
‘low’ risk circuits This group includes everything else: lighting circuits, cabling between distribution boards, and fixed appliance circuits (except bathroom).
These must disconnect in 5 seconds
