In article ,
John Rumm writes:
Jb wrote:

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

Thought as much...

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.

I could not even find evidence of a wire inside - the only obvious one
running downward from the install was the one to the gas main. If there
was a rod is it also possible it got burried when the previous owners
laid the concrete drive which continues up the side of the house beside
where the meter cupboard is located.

The right hand earth wire coming out of the Voltage Operated ELCB
should go to an earth rod, and nothing else.

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.

My plan was to measure the fault loop impeadance of what is there first
to see what the starting point is, and then add at least one proper
earth rod and carry on unitl I get a decent low enough value. Finally
add the cross bonding to the water main.

There's no point with the ELCB in the circuit -- its coil will be
of the order 100-300 ohms most likely.

If you add more earth rods to such a setup, they should be spaced
well away from the existing one, and all connected to the main
earthing terminal, not the existing earth rod. Same goes for cross
bonding. The right hand earth terminal must only go to an earth rod,
which should be outside the resistance area of any other earth rods
or equivalent resistance area around bonded services. (The resistance
area is the area around an earth rod where the ground changes potential
due to current flow in the earth rod.) The ELCB works by monitoring
the voltage between your earth conductors and its earth rod, and
tripping before it reaches 50V.

You should add an RCD nowadays, but you can leave the ELCB there
harmlessly if you lower the overall earth impedance as above, and it
provides you with a means to isolate the CU.

--
Andrew Gabriel