Earth resistance

In the US, the National Electrical Code requires that a system of made grounds (driven rods) have a ground resistance less than 25Ω. It does not say this is satisfactory, only that above this is unsatisfactory. A lot depends on your soil type and moisture.

Buried pipes and grids are sometimes used to get lower grounds and those are often only several Ohms. But, these solutions may be expensive and may be harmful to the piping system.

If the ground is used as a signal ground rather than a power ground, it will need to be much lower, perhaps 2 or 3 Ω, although ground reactance is often more important than ground resistance in signal grounds.