A Good Earthing Should?

<sigh>

What is intended to be earthed? 1MΩ is a virtual "short circuit" to static electricity charges!

The basic idea of an electrical safety earth (or ground) are pretty much the same everywhere. The case (chassis) of the equipment (and except for special situations, the internal electronics) is connected to an earth pin on the mains outlet. This is then connected through the house wiring and switchboard to an electrically solid earth point, which is commonly a (copper) water pipe, or a stake buried deep into the ground.

Should a fault develop within the equipment that causes the active (live) conductor to come into contact with the chassis, the fault current will flow to earth, and the equipment or main switchboard fuse or circuit breaker will blow. This protects the user from electric shock, bypassing the dangerous current directly to earth, rather than through the body of the unsuspecting poor suleiman who just touched it.

so 1) calculate the earth fault current for fault duration prescribed by your local standard.

2) check out the limit of step and touch voltage-Step and touch potentials determine the safety of personnel. These voltages are directly proportional to the magnitude of the fault current component discharged into the soil by the grounding network. It is therefore important to study the fault current distribution in the system.

3) calculate the earth resistance

4) based on the above information calculate electrode size and No's or grid size.

in fact above calculations have different method and complicated one, so these are done by computer generated programme. SES is the dedicated software for this purpose.