There are many factors to consider when choosing the right earthing voltage for your needs. The first is the type of earthing system you have. There are two main types of earthing systems: direct and indirect. Direct earthing systems have a direct connection between the earthing rod and the earth, while indirect earthing systems have an electrical conductor that connects the earthing rod to the earth.
The next factor to consider is the resistivity of the soil. The resistivity of the soil is a measure of how well the soil conducts electricity. The higher the resistivity, the better the soil conducts electricity and the lower the earthing voltage required.
The third factor to consider is the environment in which the earthing system will be installed. If the earthing system will be installed in an area with a lot of salt water, for example, then a higher earthing voltage will be required to prevent corrosion.