Re.
http://groups.google.com/group/uk.d-...e=source&hl=en

Sparks wrote:

You say...
"connect one end of the secondary
via a suitable length of wire to the main earth terminal in the house
and connect the other end to your earth electrode via an ammeter."

Do I assume this would be done with the rod disconnected from this main
earth terminal?

Yes, obviously - otherwise you'd have a short across the transformer
secondary.

If so, if this is a TT installation, and there is no other path to earth in
the house (plastic water pipes etc..) how will you get a reading?

Ah, yes, OK. There is an implicit assumption in that article that
you're wanting to test an earth rod for an outbuilding, etc., and the
house already has a functioning TN earth kindly provided by the DNO. If
you don't have the latter then there are probably two options:

(a) sink a third temporary electrode as far away as you can from the
other two and use that as the return connection for the test current.
You might have to increase the test voltage available to get enough test
current flowing (make sure to mask any residual voltage that might be
present between the rod under test and the reference electrode);

(b) resort to hairier methods such as using the mains neutral as the
test current return (it will be earthed somewhere), or obtain your test
current directly from the mains (phase) via a series resistance (such as
a couple of 1 kW fire elements in series) instead of using the
transformer. Clearly such methods have the potential to be dangerous,
so don't attempt them unless you have a clear understanding of what
you're doing and appreciate the dangers involved etc., etc.

If not, surely this is only testing the cable between the rod and the earth
terminal (and your test cable!), not the rod it self?

Well, quite.

--
Andy