The sensitivity will be affected to some extend.

Meaning that if the leak voltage is low enough so that it will not drive the required current because of the >15Ω Ohms earth resistence, to trip your RCCB, then it might not trip!

Nonsense.

I second your opinion. The answer (3) is shear non-sense only.

Because it trips on the difference between the phase current and the neutral current, and doesn't need an earth connection relative to itself in order to operate.

PWSlack

It trips when there is a difference and the difference will only happen if some of the current went to earth (instead of returning via the Neutral), therefore, there must be an earthing for the leak to happen and trigger the ELCB or RCCB.

...and if there wasn't an earthing then the individual touching the live part would still be safe as the current would be too low for the thing to trip.

Take a 30mA RCCB on a 240V supply. The thing wouldn't trip until the earth path resistance fell below 8kΩ. In the context of the original poster's question, 15Ω in 8kΩ is negligible.

http://en.wikipedia.org/wiki/Earthing_system

"......and if there wasn't an earthing then the individual touching the live part would still be safe as the current would be too low for the thing to trip."

How can one say that the individual touching the live part would still be safe?.The elcb will not trip, but the individual will be at risk depending on the time,amount & path of the current flow through his body & also on the other factors like if touching part is wet or dry etc...

OK, let us put it this way:

If there is a Ground connection on the equpment and a fault ocured, even a small fault through a high resistance but enough to flow the 30mA or more, the equipment will be immediately isolated BEFORE ANY INDIVIDUAL comes in contact with it to EXPERIENCE the small shock or tingle ... The grounding (Earthing) connection is to prevent any current going through any person's body, but to the ground circuit.

The neutral point must be earthed at source while all the equipment downstream will be earthed via a separate earthing point. That is; any equipment that has a metallic outer cover that could come into contact with the live circuit internal to the equipment, whether by accidentally loose wires or due to a fault occurence.

The RCD or differential c.b. will trip before any contact with a living person etc.

The OP needs to know that the earth path must be well established according to the norma governing his area, and the resisteance as low as possible.

On heavy duty installations where the short circuit to earth might produce very high currents, some protective earth resistance or shokes can be used. But this is another issue which will need professionals to deal with it!

PWSLACK:Am I wrong?.Your statement says that 30mA ELCB will give trip command when an individual touches a faulty equipment & the leakage current goes above 30mA,even if there is no earthing to the equipment safeguarding the person.Is it right?