The National Electrical Code (NEC) section 250-56 establishes a requirement for a single ground rod or ground plate to have an earth resistance of 25 ohms or less.
What is a good earth electrode reading?
for normal dry locations, or 25 (volts) for construction sites and agricultural premises. If a 30 mA RCD is used, this allows a maximum electrode resistance of 1,666 Ohms, although it is recommended that earth electrode resistance should never be greater than 200 Ohms.
