Hi if you are using an earth rod then it must read lower than 100 Ohms to fully comply with all requirements, & must also cover ALL circuits not just power!
standard best-practice is to change main sw. for time delayed 'S' type RCD, idealy of 100mA rating to give tripping discrimination. Cheaper/easier way may to ask supply company to provide earth from Neutral block instead of rod which would not require any RCD changes, most overhead systems work this way & would become PME/TN-C-S.
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