First of all: I am NOT a professional electrician, and the following is
my understanding of the power system in my country, and I shall NOT be
repsonsible for damages that happens if somebody uses this description as
a "Guide for installation".
One has to understand that powersystems can be differently constructed
and wired in different countries. I can only speak for my own country,
but I believe that it will be the case for most eurepean countries amd
most other systems using 220VAC as mains supply.
First there is a VERY important thing to know: Equipment where you may
touch metalparts like electric tools, radios with metal cabinet etc MUST
have a ground connection. Equipment that does not pose that risk may have
only two wires: Neutral and Line. This can be lamps, computers supplied
by a SMPS, soldering iron with a transforator etc.
To understand the wiring you must know how power is distributed: Normally
the mains is distributed as 3-phase high voltage to your local
neighborhood transformer. Here it is transformed to 3-phase 380VAC with a
centerpoint Zero that is grounded directly at the transformes site. Power
is then didtributed to the user as 3 phases and the grounded line named
Neutral. Or you could have 1 or 2 phases and 1 Neutral. The voltage
between Neutral and any phase is 220V, and between any 2 phases 380V
At the entrance of your house you have yet a groundconnection: 2-3 meters
of iron rod in the ground.
So at your service now you have 5 wires: 3 phases, 1 neutral and 1
ground.
These are routed trough a device("fault current relay") that measures the
current between ground and any of the four lines. If that current becomes
too big (>10-20mA) it cuts out everything. That protects your life(been
there, done that, got scared)
For 220V-Single phase devices You can have wall outlets with two or three
connections: 1 - Line and Neutral, and 2 - Line, Neutral and ground,
depending on what type of equipment is going to be used. With a 2-wire
outlet you have no way of knowing which line is live or neutral, whereas
it is well defined with a 3-wire outlet.
For 2 or 3-phase devices(Powertools - PA's etc) You can have a 3-phase
outlet with neutral and ground. Some devices may use all four - some
other only the 3 phases and ground).
Personally I use 3 and 5-wire outlet for all my equipment - radios and
measuring devices for several reasons: 1-Protect myself against failing
equipment, and 2-Protecting the equipment against static charges that
could damage sensitive inputs.
Hope it clarifies - sorry for the bandwith.
Best 73 de OZ5TG, Verner
----- Original meddelelse -----
> Fra: Jim Garland <4cx250b@miamioh.edu>
> Til: amps@contesting.com
> Dato: Tir, 15. okt 2013 15:12
> Emne: Re: [Amps] More on two pin 220vac
>
> Paul has raised a pertinent issue. I find it hard to believe that the
> power
> distribution in Thailand or any other country is completely floating
> with
> respect to ground. Were that the case, then the entire concept of a
> "neutral" would have no meaning. In HV power supplies which have a B+
> and a
> neutral current return, one always anchors the neutral line with a
> resistor
> (100 ohms typical) to chassis ground. This is done to keep the B+
> from
> soaring uncontrollably. The same reasoning applies to an AC power
> distribution system.
> 73,
> Jim W8ZR
>
> > -----Excerpt from Original Message-----
> > > > about 80% of Thailand buildings have TWO holes in the 220VAC
> wall
> sockets
> > > and ONLY TWO HOLES. One side is definitely hot and the other side
> is
> > > definitely neutral. The pin sockets, the holes, are not marked
> and not
> > > keyed in any way. There is NO GROUND present by any means...no
> wire
> > > ground, no BX cable nor conduit.
> >
>
> > 1) Is the receptacle keyed in any way to ensure proper hot and
> neutral
> with
> > mating plug connections?;
> > 2) Is the neutral absolutely floating above all grounded and
> grounding
> > conductors (e.g, a water pipe or water-fed room radiator)? That of
> course
> > assumes piping is even grounded in Thailand. Or, is neutral simply
> a
> > floating return for the hot (which in reality would make it another
> hot
> > conductor). Even though the receptacle has no ground reference, is
> neutral
> > grounded/earthed at the service entrance or at some point upstream
> from
> the
> > utility provider?
>
>
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