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List:       opensuse
Subject:    Re: [opensuse] KTp alternative to Skype?
From:       Greg Freemyer <greg.freemyer () gmail ! com>
Date:       2014-05-06 19:42:57
Message-ID: CAGpXXZ+w4k3gvevXFj71fE0Uk6hknNsmO=r9rQn3CirrM2DLFw () mail ! gmail ! com
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On Tue, May 6, 2014 at 3:23 PM, Per Jessen <per@computer.org> wrote:
> Greg Freemyer wrote:
> 
> > On Tue, May 6, 2014 at 2:26 PM, Per Jessen <per@computer.org> wrote:
> > > > Using a 2-phase US circuit to simulate a 1-phase 220v circuit would
> > > > be dangerous if there are devices that depend on one of the legs
> > > > being ground.
> > > 
> > > I suspect you mean neutral instead of ground?
> > 
> > At least here neutral and ground are very similar.
> > 
> > A standard US household circuit breaker panel has:
> > 
> > phase 1 hot
> > phase 2 hot
> > neutral - return
> > ground
> 
> The standard household supply here has one more phase, otherwise the
> same.
> 
> > The neutral & ground are actually tied together inside the circuit
> > breaker panel.
> 
> Not here, not at all. Any current running to ground is a fault, and will
> cause the residual-current circuit breaker to pop. According to
> wikipedia, it is called a "Ground Fault Circuit Interrupter" where you
> live.

We have GFCI plugs and they are typically required near water
(sinks/kitchens/bathrooms).

But here the GFCI is only used after the circuit breaker.  James can
correct me, but I am fairly sure any current flowing in the neutral
lines inside a building is transferred to the ground at the circuit
breaker and from there it flows to the outside ground/earth/dirt.

The phases are 180 degrees out, so if you have exactly a 100 amps of
load on both phases, the net electron flow on the ground line leading
to the dirt is zero.

But in general the ground/earth/dirt is the return back to the power station.

> > Further, both are often connected to a copper cold water line. By code
> > that has to happen close to where the cold water  line enters the
> > building.  I know my house works that way, but there is also a second
> > ground spike driven directly into the ground that is also tied to the
> > circuit breaker panel ground and neutral.
> 
> Wow.  I'm familiar with the ground spike and the clamp on the cold water
> pipe, but not the rest.

I am 100% sure that the outside ground/earth/dirt is connected to both
that inside ground lines and the neutral lines at the circuit breaker
panel.

I am not 100% sure there is not also a copper neutral return line to
the power company, but I don't think there is.

> > Thus in theory the "ground"/neutral is actually a part of the 120volt
> > circuit. and both the ground lines and the neutral/return should have
> > close to zero volts differential to the outside dirt (ground).
> > 
> > The fundamental difference here is that the ground lines running to
> > every plug don't typically carry any current except in a failure mode.
> 
> Right, same here.
> 
> > The neutral/return is meant to carry current routinely.
> 
> Right. So why are they tied together in the circuit breaker panel?

Because the outside dirt is the fundamental return as I understand it.

With a standard single phase 3 wire setup, the ground line is tied to
the device chassis and the power runs in the hot and return.

Because of that if you look at a standard US household in wall
electric cable, the hot and return are individually insulated.  The
ground is not although it is inside the overall cable sheathing.

> > fyi: if a circuit breaker panel is perfectly balanced the electrons
> > flow only in the 2 hot lines and in the neutral. No electron movement
> > would take place in any of the ground lines including the real ground
> > outside.
> 
> Right - dunno if I would call that perfect, for the single phase circuit
> it's just normal.  In the 3-phase setup, with a perfectly balanced
> load, you have no return current on the neutral.
> 
> > Such perfect balancing is impossible to achieve so electrons
> > are moving in and out of the earth continuously in a US system.  I
> > assume the same is true for the EU.
> 
> A bit out of my field, but I don't think so. Current running to ground
> will cause the FI Schultzschalter to pop.
> 
> One of these:
> http://w3.usa.siemens.com/powerdistribution/us/en/product-portfolio/circuit-breakers/residential-circuit-breakers/gfci/pages/gfci.aspx
>  http://www.conrad.ch/ce/de/product/628056?insert=UP&WT.mc_id=googleshopping_b2c_chd&WT.srch=1&gclid=CLfb1t6AmL4CFZShtAodgyoAaw
>  http://www.distrelec.ch/de/FI-Schutzschalter-63-A-300-mA-4-polig-415-VAC-Schneider-Electric-FI-3L-N-23478/p/13609855?q=fi+schutzschalter
>  

Again, I'm petty sure in the US we routinely have electron flow in the
outside ground, but not in the inside / post circuit breaker ground
lines.

I am pretty confident we don't have a GFCI or equivalent monitoring
the outside ground line.

> --
> Per Jessen, Zürich (18.1 °C)

Greg
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