TENTECH MD-5075x, User Manual

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5. Use of “Guard” (G) terminal
Depending on the measurement to be made, the Guard (G) may be used
or not. During the measurements, the equipment should be electrically
grounded to avoid unsteady readings. When insulation is measured
regarding grounding, the
R terminal is connected to earth and the
condition by means of which the equipment potential setting is fulfilled. If
the measurement is performed between two parts, which are not
grounded (for example, between two phase conductors in a three-phase
cable), the equipment
GUARD terminal must be grounded. This implies
that whenever a measurement is performed, one of the GUARD or R
terminals must be grounded, but not both of them simultaneously.
Technical Note 32, reproduced at the end of the manual, explains the
usage of GUARD terminal in order to eliminate the parasite resistance
effect over the result of measurements.