A question was asked recently about electricity distribution in
New Zealand.

In much of the world outside the US, the electricity distribution
system is described as Multiple Earthed Neutral (MEN).  In this system,
each low voltage (LV) supply transformer is a 3-phase design with three
separate windings arranged in a Star connection.  The central star
point is the neutral connection and this connection is always earthed
at the supply transformer location.

Electricity supply to consumers is either single-, two- or three-phase,
and uses the neutral wire plus either 1, 2 or 3 phase connections.
Most consumers have a single phase supply.  The voltage from the
central star point, or neutral, is 220/230, and the phase to phase
voltage is 220/230 times square root of 3 = 220/230 x 1.732 = 380/415
volt.  At each consumer's switchboard the neutral is earthed.

Australia/NZ is a 415 volt area, but Europe is a 380 Volt region.
There is a gradual tendency to align Oceania to Europe.  This change
will take decades to achieve.  Even within Australia, The relatively
isolated State of Western Australia has a somewhat higher voltage of
around 240/250 Volt, and this is being, (or has been) adjusted to
220/230 volt.  The WA grid is not interconnected with the Australian
East coast grid.

In the US system, my understanding is that each 3 phase LV supply
transformer has 3 separate windings, but these windings are _delta_
connected.  Each winding is 220 volt and is also center tapped
(center tapped?).

From each centre tap to the phase connection, there is 110 volt.
Each consumer gets a 3 wire connection; the neutral, plus the two
phase wires.  The 3 centre tapped points on the transformer are
connected together to form a single neutral, and this neutral is
NOT connected to earth, but floats at some potential near to earth
potential.  I believe all the countries that use the US system are
like this (Philippines, Japan etc).

With industrial supply systems, I believe the supply is 480 volt MEN.
Each phase to neutral voltage is then is 277 volt with the windings
being star connected.

Australia and New Zealand are in lock step with standardisation
perspectives.  As well, both countries are locked in to the IEC
standardization regime.

Hope this is of some interest.

Paul Rumpf.
Melbourne, Australia.

 [ North American residence service is 120-0-120 3-wire split phase,
 [ neutral earthed at the house electric service entrance ("fuse
 [ panel").  Newer 3-phase industrial service is 120/208 4-wire wye.
 [ A local transformer bank reduces the HV supply via delta-connected
 [ primary to wye-connected secondary.  This delta-wye connection
 [ reduces odd harmonic distortion products.  -- Robbie