Amprobe GP-1 Earth-Tester-Ground-Probe - Manual (Page 11)

Electrode Resistance:
Test C & D
(cont’d.)
Page 11
5) Clip the BLUE test cable (C2) to the 100% test rod and clip the RED (P2) test cable to the
test rod at the 62% mark.
6) Turn the GP-1 ON.
7) Press the START button until a stabilized result is displayed, then release.
52%
P2
P2
P2
P1
C1
C2
62%
72%
100%
BLACK
GREEN
RED
BLUE
at
at
at
at
Calculate distances between the test rods using formula below:
C2 = (Depth of the electrode or diagonal of the grid system) x 4
FORMULA 1 P2 at 52% = C2 * 0.52
P2 at 62% = C2 * 0.62
P2 at 72% = C2 * 0.72
For example: To test single 10’ deep electrode use following formula:
C2 = 10’ x 4 = 40’
P2 at 52% = 40 * 0.52 = 21’
P2 at 62% = 40 * 0.62 = 25’
P2 at 72% = 40 * 0.72 = 29’
Note: Inside the top cover of the GP-1 you will find a simplified formula which uses 100 ft. or
longer distance for electrode C2. This formula holds in most cases, however, in order to get
the most accurate measurements we recommend that you use the formula from this manual.