On 08/07/2019 22:27, wrote:

I'm new to earth rods so would like a little advice.
First, some background. We bought the house a couple of years ago and at
that time it was supplied via a 2-wire overhead line from a transformer
some (unknown) distance away. The 2 wires terminated on a bracket at the
back of the garage and then came through the wooden window frame to the
main fuse. As soon as we moved-in I got the local electricity board to
put the final leg underground and convert the supply to TN-C-S - it
looks as if they have added a ground connection at the final pole but
the existing connection to a local earth rod was left in place.
I'm replacing the old CUs as part of a major refurb and decided to keep
a local ground rod, but to use a different position. I've just put a 4ft
rod in the ground and made some measurements (using 30V DC and checking
with both polarities). The soil is clay and the rod went-in remarkably
easily using the SDS hammer.
New rod to MET: 60 ohms
Old rod to MET: 150 ohms
New rod to old rod (about 4m apart): 230 ohms

60 ohms seems rather high - what impedance should I be aiming for and is
there any point (with clay soil) in driving the rod down another 4'?

60 does sound a bit higher than I would expect (I have found getting
under 15 is usually easy with a single length rod in clay). It might be
worth trying a different location. Having said that, if you have TN-C-S
anyway, you have to question what you actually want to achieve.


--
Cheers,

John.

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