"mick"

The basic principle of Class II is *NOT* to rely on the mains earth for
user safety.

Two reasons:

1. If the mains earth connection is missing anywhere, the equipment
still operates ( with no warning to the user) and you have no safety.

2. If the AC outlet or equipment plug is miswired, active can appear on
the earth conductor and you have a lethal situation.


The principle of Class II is that there is NO REQUIREMENT to rely on
earthing for user protection at all,

** Not correct.

There must be NO earth connection made to the item.

The familiar notice reads:

" Double Insulated Do Not Earth. "
-------------------------------------


A very nasty example of scenario "2" occurs when the equipment plug has
earth and neutral wires reversed - which goes unnoticed until the day it
is plugged into an outlet that has active and neutral reversed.


Agreed. It's only relatively recently that domestic wiring in the UK has
been using earth-leakage protection. Older installations (including my
own!) don't have it - in fact, I'm still on rewirable fuses here!
Consequently we tend to be careful about wiring plugs & sockets up
correctly. Even when properties are being refurbished over here, there
is no legal requirement to change any existing distribution boards etc.
unless they are damaged. Consequently there are a lot of houses in the
same condition as mine.


** Much the same situation exists in Australia, though it varies from state
to state.

Interestingly, in the USA it has been compulsory to fit safety devices to AC
outlets in bathrooms for decades.

Originally they used mechanical "core balance relays" instead of the modern
electronic version.


.... Phil