On my opinion it has a small meaning talking about potentials between ground
and neutral, what counts is the amount of current that eventually flows and
this has to be kept minimal.
Differential safety switches (few mA) are just and obligatory installed at
houses and plants (E.C. rule) to dectect and stop disperded current flows,
i.e because of defective isolament of some appliance, from phase to ground
instead between phase and neutral like it should be.
In Italy, the neutral is grounded at houses basement or at transformer site
(15Kv-380V) if closer than a stated distance that insures low ohmic
resistance between the two grounds.
The differential switch is actually placed between a local ground point and
the neutral wire, naturally, to make the system working properly the best
is when the resistance between neutral ground and local ground is minimal
and the optimal case is when they came from the same point.
In any case, it's now impossible to "get free" more than a few mA, and risks
for people are minimized .
73,
Mauri I4JMY
----- Original Message -----
From: "Peter Chadwick" <Peter_Chadwick@mitel.com>
To: <amps@contesting.com>
Sent: Monday, November 20, 2000 11:22 AM
Subject: RE: [AMPS] Grounds
>
> Thanks for all the comments.
>
> Here we have a totally different system The power line down the street is
> usually buried, and has 3 phases and a neutral. The neutral is grounded in
> various places, but not necessarily at the house. However, the ground
leads and
> metalwork in the house can be connected to the neutral - it depends on
whether
> or not one has what is called 'Protective Multiple Earthing'. This can
give
> major problems if you've an external ground and one gets a ruptured
neutral. In
> country areas, one can have a 2 phase line (i.e. 2 of the 3 phases)
distributed
> around. So we always get neutral and phase, which gives a NOMINAL 240 or
> therabouts. NOMINAL means just that and it can vary wildly! The neutral is
> theoretically at ground, but when I lived in town, I could get 24 volts at
1/2
> amp free from neutral to ground.......
>
> Where I am now, the neutral is grounded on the pole outside the house; the
house
> has a separate ground rod to provide the ground, and the neutral is
usually
> within a volt of ground. Fortunately, we don't get the lightning problems
you
> guys abroad get....
>
> Thanks agn for the info.
>
> 73
>
> Peter G3RZP
>
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