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-... 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-Sch...
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)
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