In article ,
"nightjar" writes:

The whole idea dates back well before ISO 9000 or even BS 5750. It comes
from practical experience in the electricity supply industry of what has
killed people in the past. You cannot assume that the cable clamp will be
fitted properly, if at all, and if the earth wire disconnects first, leaving
the other two connected, there will be no reason for the average user to
suspect a fault. However, a fault to earth within the appliance will make
the case live, rather than tripping the circuit protection.

One reason that moulded on plugs are required on new equipment today is

I don't believe _moulded on_ plugs are required, just that appliances
are supplied with a fitted plug, unless there's a more recent update
to the plugs and sockets regs which I haven't seen.

that, historically, amateur electricians have managed to find so many
different ways to kill people with rewireable plugs. I was once bought a
kettle that was not working, only to find that the person who had fitted the
plug had connected the earth wire to the live terminal. Fortunately the
owner had only held the metal kettle by the insulated handle.

--
Andrew Gabriel