20 Apr
1999
20 Apr
'99
10:42 a.m.
First, to get common names:
Hot = one Phase
Neutral = Protective Ground
Ground = Ground (the starpoint on 3 phases connected to earth at the
'generator')
That explains the confusion. In the US:
Hot is one phase and in single phase systems you can and do have 2 hots.
Neutral is what you are refering to as ground. The starpoint for both
single and 3 phase.
Ground is the protective / frame ground.
The protective ground (ground in US codes) is not allowed to normally carry
any current. It should be able to be temporarly disconnected and not create
a hazardous condition.
Second, do I understand that US appliances got fuses on
both wires
and both are switched ?
On 240 volt equipment yes.
The 120 volt plugs are defined with distinct Hot, Neutral and ground pins.
I am familiar with your plugs also and have wondered how hot / neutral
definitions are handled. Think of US 120V plugs like UK plugs just smaller
and without fuses in them.
Over here in Germany only one wire is
switched and protected with a fuse, althrough it is not defined
which one is the 'hot' line, since our connector is symetrical
- there is no way to insert the plug in a way where the Hot and
the Ground side is defined - Our plug isn't inherited from the
DC times, but rather a new design when 220V AC became standard
in the 30s, to fit the needs of (and only of) AC Eq.
The US did not used to make a distinction between hot and neutral until
about 30 years ago when they added the "protective" ground pin. Now they
are keyed. If you look closely at a receptacle, one blade is wider -
neutral, The narrower blade is Hot and the round pin is protective ground.
Some "equipment" uses only 2 wires. The blades and often one is larger to
assure that it is polarized correctly. These polarized plugs have come into
common usage in the last 20 years.
Dan