Hi Ed:
With few exceptions, most power distribution
systems have one pole of the supply, the
neutral, grounded. (Indeed, the definition
of "neutral" for single-phase systems is the
grounded conductor.)
In the IEC scheme of the world, a power
distribution system where the neutral is
grounded is known as a TN or TT system.
The first letter identifies the grounding
scheme for the neutral wire. The second
letter identifies the grounding scheme for
the protective wire.
T = terra (a ground rod)
N = neutral
In North America, the scheme is TN. The
neutral is connected to a ground rod at
the service entrance. The protective wire
is connected to the neutral in the breaker
panel.
I believe Korea uses the TN system. So,
at any socket-outlet, one pin will be at
the phase voltage, 220, and the other pin
will be at the neutral voltage, 0.
Polarity is a separate issue. By polarity,
I mean that the neutral identification is
maintained through the plug/socket-outlet
scheme.
Polarity is not maintained where the plug
can be reversed in the socket-outlet. The
SCHUKO plug is a plug that can be reversed
in the socket outlet. Not only that, but
the socket-outlet is symmetrical, so the
wiring to the socket-outlet cannot be such
that the neutral is always wired to the same
pin.
Among the world's plugs/socket-outlet
combinations, relatively few maintain the
polarity through the system. These are:
the British 13-A plug/socket-outlet in
UK, Ireland, Hong Kong, Singapore, etc.
the old British 15-A plug/socket outlet
in South Africa and India, etc.
the Australian plug/socket-outlet
the North American grounding plug/socket-outlet
the North American two-wire plug/socket-outlet
with one wide blade
The French plug/socket-outlet with its
grounding pin scheme COULD be polarized, but
is not so wired. Likewise, the Danish,
Chilean, and Chinese plug/socket-outlet
could be polarized, but I cannot say if they
are.
Polarized plugs and socket-outlets always
bear markings indicating the pole of each
pin. For North American plugs and socket-
outlets, the white or silver-colored screws
or terminals are the neutral pins. Other
plugs and socket-outlets bear molded in
letters such as L, N, E or PE or G.
Virtually all safety standards include the
requirement that the neutral wire within the
equipment shall be treated as if it was at
mains voltage rather than at zero voltage.
This is because, in many installations,
errors may occur in the wiring of the socket-
outlet.
Best regards,
Rich
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