This is without doubt an old voltage trip and needs scrapping.

Many properties of this age were earthed to a rod using steel wire and over
the years lost the connection to rust so it may well have disappeared by
now.
Asking how many earth rods is a bit like asking how long is a piece of
string. You need a meter to check (not a multimeter) the final earth
resistance. Don't make the common mistake of banging in rods close to each
other thinking more is better; getting them too close actually increases the
resistance. In clay you probably only need one but you buy a 'proper' earth
rod they will screw together to achieve a greater depth should you need to.


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