On 26/12/2017 15:48, George Miles wrote:

Whats wrong with ' overlapping resistance areas ' ?

Within a single installation, it just means that the rods don't behave
as fully independent connections to earth - so its better to test them
as a single system rather than in isolation.

Its more problematic when different dwellings have supposedly
independent connections to earth but they are via electrodes with an
overlapping resistance area. Then a fault current flowing to earth from
one property can induce a voltage to be present on the other properties
earthing system.

John Rumm wrote:
"Multiple rods are ok (and are commonly used in the supply side of PME
installations for example), but ideally don't want to be too close
together such that they are in overlapping resistance areas. "

The existing earth rods are about a yard outside the backdoor,
the proposed indoors one would be just inside the back door under the consumer units.

The existing TT earth inductance was measured a new weeks ago and was OK,
but I dont have the figures here.

[geoorge]



--
Cheers,

John.

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