Electrical Engineer

IEE 16th edition requires that the minimum conductor size be half the size of the main earthing conductor, for 100A installations a main earthing coductor of 16 mm² and a bonding conductor of 10 mm² will meet requirements where the supply neutral conductor is not more than 35 mm² It is recommended that the earth fault loop impedance does not exeed 220 Ohms. Taken from IEE on-site guide.

It depends on the countries local standards & regulations and the specific application (intrinsic safety earths for a hazardous area installation have a lower limit than say a houshold earth system).

More information is necessary.

It depends on the location and Country govt rules. For example (Industiral) in dry areas in India should be less than 2 ohms and near sea shore 0.5 ohms max.

3 ohms

Check German VDE they have very specific requirements for many of grounding systems.

It actually depends on type of grounding needed. Most installations, and codes, lean toward low resistance grounding to facilitate braker triping in the case of a phase to phase or phase to ground fault. But there are installations that require high impedance grounding. This impedes breaker trips in the event of a fault for situations where shutting down a process is more detrimental then shortening equipment life. Check out www.i-gard.com for resources on this topic.

This is dependent upon the country and municipal regulations. In the US, it is 25 ohms between the ground and the electrode.

What about The Computer? One Ohm?

What about common with lighting protection?

What about section of the grounding grid / web?