Double Earthing

Lyn,

Your understanding of 'Guru' is just what you seem to know in your context. BTW, it is also a name of a person in some cultures and this is what it purports to be in this case, so I suggest you use your barbs only when you are absolutely certain of what you know!

Double earthing or double insulation?

Do you mean double insulated as denoted on equipment such as electric drills by a square within a square?

Two separate earth connections. If one fails, the other is intact, so the operator is safe. Paraphrasing lyn's "Belt and suspenders(braces in English English) ", if one fails, the other is still there to keep the pants up

Re: "If one fails, the other is intact, so the operator is safe."

This can cause problems if it is done improperly, especially in instrumentation / control systems. You don't want to cause currents to circulate in the neutral or shield of instrumentation wiring.

Human Safety takes precedance over equipment/instrument safety. If anything is done "improperly", it will cause trouble. If double earth connection - done improperly - causes problems to instrumenttaion/control systems, what if the 'only' earth conection is also done improperly?

I don't know about double earthing. But with an 11KV 1000KVA I would run 3 X 95mm. one each to the HV connection, the tank and the LV connection box.

Just a little bit more on this, (and I guess we have gone too far from the OP).

The OP should show more clearly of where this double earthing is applied. Since this would make other people confused and misunderstood.

I think that there are more than three systems called "double earthing" existed.

1. Equipment "double earthing", which is applied to a large machine. This will be done separatelly from the system earthing. It means to say that the first earthing is failed. We have another one.
2. Lightning Down Conductor: Sometimes we have to use 02 down conductors connected to the earth mesh. It does not mean that because of we using smaller conductors. We need to have two separated earthing system and run down with two conductors to these separated earthing mesh. According to the size of the facilities needed to be protected, the 02 or more down conductors would be required.
3. Double earthing: As we stated above, this kind of earthing willl require two down conductors to the earth mesh and is applied for sytem earthing. The purpose is to backup when one of them broken.

The way I read this is that you are proposing to install 2 grounding/earthing conductors in parallel between the equipment and the system ground grid?

That is simply a matter of conductor redundancy, not double grounding which I take to be the installation of two electrically isolated grounding systems. Nothing wrong with that, but again why not do the installation right in the first place?

Not really install in paralell. They would be connected to separated locations.

Hell, I have four types of ground at my installation. Each has its own purpose, but as pointed out, they all come together at common points.

Seems like the poster is referring to a redundant type of system for something that may be subject to physical damage, hence the "backup" ground connection.