36
Digital Ground Resistance Tester Model 4500
4.10 Multiple Electrode System
A single driven ground electrode is an economical and simple means of
making a good ground system. But sometimes a single rod will not provide
sufficient low resistance, and several ground electrodes will be driven and
connected in parallel by a cable. Very often when two, three or four ground
electrodes are used, they are driven in a straight line; when four or more
are used, a hollow square configuration is used and the ground electrodes
are still connected in parallel and equally spaced (Figure 21).
In multiple electrode systems, the 62% method electrode spacing may no
longer be applied directly. The distance of the auxiliary electrodes is now
based on the maximum grid distance (e.g. in a square, the diagonal; in a
line, the total length. For example, a square having a side of 20 ft will have
a diagonal of approximately 28 ft).
DIAGONAL
DIAGONAL
a
a
a
a
Figure 21
