ERICO EST401 ERITECH Clamp-on Ground Resistance Tester - Manual (Page 18)

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Field Applications
Pad Mounted Transformer
Observe all safety requirements - High voltage may be present!
Locate and number all rods (usually only a single rod is present). If the ground rods
are inside the enclosure, refer to Fig. 17 and if they are outside the enclosure, refer
to Fig. 18. If a single rod is found within the enclosure, the measurement should be
taken on the conductor just before the bond on the ground rod. Often, more than
one ground conductor is tied to this clamp, looping back to the enclosure or neutral.
In many cases, the best reading can be obtained by clamping the instrument onto the
ground rod itself, below the point when the ground conductors are attached to the rod,
so that you are measuring the ground circuit. Care must be taken to find the conductor
with only one return path to the neutral.
Generally < 0.7Ω indicates that you are on a closed loop. In Fig. 18, the ground rod
is located outside the enclosure. Clamp at the indicated measuring point to obtain
the correct reading. If more than one rod exists at different corners of the enclosure, it is
necessary to determine how they are connected to properly measure the ground resistance.
Figure 17
Figure 18
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