On 20 Apr 99 at 18:32, Hans Franke wrote:
> > >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.
>
> Sorry, just my translation problem, I had to assign names where no
> dictionary could help me, And Neutral = Protective Ground vs Ground
> seemed to be logical - sorry.
>
> > The protective ground (ground in US codes) is not allowed to normally carry
> > any current.
>
> Same over here.
>
First of all it should be called NA standards as Canada is also part of the NA
grid and has TMK slightly more stringent standards. The Generating station
transmits through the Bulk Transmission System at 500kv to a regional
Transformer station which retransmits at 230kv via the Regional Supply System
to a local Transformer station which then supplies Municipal and local
distribution systems at 600v. Typical residential and small commercial supply
is then provided with 240v single phase. Larger commercial or industrial supply
is 3phase 208v or 600v measured phase to phase. As an aside, the large mobile
generators seen on movie sets generate 3 phase 208v because of lighting power
demands.
The correct terminology here is Line, Neutral, and Isolated Ground. equivalent
to the red or black, white, and green wires. Because of fluctuations in supply
the neutral to line configuration is referred to as 110/120 while the line to
line one is 220/240. Most higher-power or supply critical 110/120 devices use
the 3prong plug. Cooking ranges, dryers , and some air-conditioners use the
220/240 configuration and now must in most jurisdictions use 4prong plugs.
Usually red, black. white, and green wiring.
Where problems arise is that most older wiring does not comply to the
new(relatively) specs regarding grounding, much less the keyed plugs. There
are many houses still with 2 wire systems and an adapter called a "cheater" is
available in most hardware stores to circumvent the 3 prong grounded plug. It
has a ground wire to attach to the faceplate screw, which most people ignore.
Even that supposes that the switch receptical is properly grounded via the coax
cable used in many older installations. I have also seen 3-wire 220 without any
ground in many older houses.
> > >Second, do I understand that US appliances got fuses on both wires
> > >and both are switched ?
> > On 240 volt equipment yes.
>
Not always.
> Ahh ja - we also use fuses in each 'Hot' wire - so if you have a
> 3~ installation, 3 fuses are to be installed _and_ they have to
> be tied (mechanical), so if one blows all 3 will go off.
>
> > >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.
>
I think the keyed plugs have more to do with modern equipment needs such as
X-10 (? the control system) ,than safety or power quality concerns.
> Strange, but common - I don't know any reason why the system has
> to be keyed, I always assumed the US development of keyed plugs
> was triggered by old DC systems (since in DC Eq. it is necersarry
> to know the orientation), but not a new addition. Strange, we
NA switched from Edisons DC systems as in NYC to Tesla/Westinghouse AC
early on due to the better power transmission over the greater distances
occasioned in NA.
> dropped all orientationwhen switching to AC (with Protective
> Ground). Could anyone give give a reason why the system has
> to be keyed _IF_ a Protective Ground is included (other than
> define the Protective Ground pin) ? Because, without Protective
> Ground a definition of Neutral is essential, but with, no longer.
> I'm realy courious, since this is the kind of technology I'm
> originated - I studied Starkstromelektronik (Power Electronics)
> after (high)school.
>
> Thanks
> Hans
>
There also has to be a differentation made between safety ground
and signal ground. AC power ground is generally only at low impedance
at low frequencies. Also if signal and power ground is connected at
more than one point, a ground loop can be created as I'm sure you're
aware.
One of the differences between the Canadian Electrical Safety Code
and it's US counterpart the National Electrical Code is that Isolated
Ground circuits must bypass the panel board and be connected to
"Earth Ground" at supply entry. This avoids any interaction with the
supply panel.
ciao larry
lwalker_at_interlog.com
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Received on Tue Apr 20 1999 - 20:50:18 BST