Extech Instruments 382356, User Manual, Page: 7 / 13

382356 V2.0 5/03
7
Principle of Operation
Typical multi-grounded distribution system.
If the parallel ground resistances,
R
1
, R
2
, R
3
,etc, up to R
n
are combined
as R
eq
, then only R
g
and R
eq
are
left in the circuit
If a constant voltage is applied to the circuit, the following equation applies:
eq g
R R
I
V
+ =
where:
n i
R
R
i
eq
,... 2 , 1 ,
1
1
=
∑
=
If R
g
and R
1
, R
2
, R
3
…R
n
, are approximately the same, and n is large (200, for example),
then R
eq
will be much less then R
g
and may possibly approach zero.
Example:
If R
g
and R
1
, R
2
, R
3
…R
n
are all 10
Ω
respectively and n = 200, then R
eq
by calculation
equals:
Ω =
+ +
=
05 . 0
10
1
...
10
1
10
1
1
eq
R
Rn R
2
R
1
R
g
V
I
R
eq
Rg