Dear William,

A sentence starting with "May I say..." is not a claim.

Too the OP, sorry for digressing.

So if someone were to say to you, "May I say that all birds are ducks," you would not comment on it because it is not a claim?

But, by all means, I obviously completely misread your statement. Could you please explain what you DID mean when you stated, "May I say, as a the most basic conclusion, that in any circuit the only thing that a schematic cannot lack is "common" (properly denoted by the triangle shown below)?" Apparently, you did NOT mean that in any circuit the only thing that a schematic cannot lack is "common", but I can't figure out anything else that you might be trying to say.

 

In ALL likeliness Neutral and Ground are connected at one point for a buildings distribution system.
This makes any metal, pipes etc, to be at the earth's potential.

In the US, we had a two wire distribution system, but the metal electrical outlets were grounded.
So, three wires to the box, but only two available for power.

Theta ground, we call protective ground because it should only carry current under a fault condition.

Since it doesn;t carry current, it is also a reference.

Stuff can get a bit messy when outlets are paralled because in an initerior lightning strike to a single circuit, the reference potentials of the series connected element will be off.

In the US we have something called an "isolated ground" in an industrial setting. This just means that the ground wire goes all the way back to the bonding point.

Hospitals and radio transmitters may actually have a reference ground and a fault carrying ground wire.

For a given system there should be only one reference point, but the earth is not at the same potential everywhere. Thunderstorms can change the local earth's potential.

Where this matters is when you install concrete around a swimming pool. This installed in such a way that it's close to equipotent, The rebar (steel reinforcement) is welded together before the concrete is poured and it;s earthed so there is no gradient. The water also sees the same earth, You don;t want a shock when getting out of the pool or when touching the concrete and the nearby Earth.

It's important to keep grounds separated and tie them together at only one point. AT least that's your general goal. e.g. High current commons should not be intermixed with reference commons. They can be connected together at one point relative to the system.

 

KISS,let me be so bold as to clarify some of your statements. The ONLY way that any metal, pipes etc are at earth potential is if they are connected in some way to EARTH ie a pipe copper or steel pipe runs underground or through concrete of a building. Simply connecting NEUTRAL and GROUND(or the EARTH wire) together will not connect same to earth potential. One needs to place a suitable EARTH rod in the SOIL (usually at the source of power) and connect the Neutral and earth wire to the earth "stake'".
Here we have what we call a "MEN" system (multiple earthed neutral) whereby EVERY switchboard has an earth stake of correct size driven into the ground and the neutral is connected in the switchboard via a "neutral earth link". Every power point(and now all light fittings) have an earth conductor which is either connected via a three pin plug to an appliance or hardwired(stoves, hot water etc).
All metal parts of an installation or appliance must have an earth conductor(part of the 3 core cable installed) unless it is classed as "double insulated", then it only needs 2 core lead(active , neutral).
When installations are tested there must be no more than 0.5 ohms resistance between any power point earth and the main earth stake so protection equipment will properly trip on an earth fault.

 

Hola William again

A question mark, denotes a question. I expected a direct answer.

Thanks for taking the time to reply.

 

KISS,let me be so bold as to clarify some of your statements. The ONLY way that any metal, pipes etc are at earth potential is if they are connected in some way to EARTH ie a pipe copper or steel pipe runs underground or through concrete of a building. Simply connecting NEUTRAL and GROUND(or the EARTH wire) together will not connect same to earth potential. One needs to place a suitable EARTH rod in the SOIL (usually at the source of power) and connect the Neutral and earth wire to the earth "stake'".

True. I was basically biased when I wrote this because my house does not contain a ground rod. It does, however use the copper pipe. I agree, I was not totally clear.

Just to clarify, the "single point earth ground" is "close enough". We have the uffer ground. https://en.wikipedia.org/wiki/Ufer_ground here https://en.wikipedia.org/wiki/Ground_and_neutral there is a mention of multiple ground rod connections.