Measurement Principles - Extech Instruments 382357 User Manual

Measurement Principles
Typical multi‐grounded distribution system
If the parallel ground resistances,
R , R , R ,etc, up to R
1 2 3
as R , then only R
eq
left in the circuit
If a constant voltage is applied to the circuit, the following equation applies:
V
I
If R and R , R , R
g 1 2
will be much less then R
Example:
If R and R , R , R
g 1 2
are combined
n
and R are
g eq
 
R R
where:
g eq
...R , are approximately the same, and n is large (200, for example), then R
3 n
and may possibly approach zero.
g

...R are all 10 respectively and n = 200, then R
3 n

R
eq
1
10
V
 
R R
g eq
I

R
eq

1

. 0
1 1
 
...
10 10
  
10 . 0 05 10
7
R
eq
I
Rg
V
1

, i 1 2 , ,... n
1
R
i
by calculation equals:
eq

05

. 05 R
g
382357‐EU‐EN V2.4 2/13
eq