HT instruments M71 - Manual (Page 16)

M71
EN – 15
4.4.2. EARTH 3W- Measurement procedure
CAUTION
The instrument can be used for voltage and current measurements on
installations with overvoltage category equal to CAT III 240V to earth and
maximum voltage of 415V between inputs. Do not connect the instrument to
installations whose voltages exceed the limits indicated in this manual.
Exceeding such limits may cause electric shock to the user and damage the
instrument.
Fig. 6: Instrument's wiring for three-wire earth measurement
¾
For small sized installations, place the ampere metric probe (terminal H, blue wire) at a
distance equal to five fold the diagonal of the earth installation and the volt metric probe
(terminal S, red wire) at a distance equal to about 2.5 times the diagonal of the earth
installation
¾
For large sized installations, place the ampere metric probe (terminal H, blue wire) at a
distance equal to the diagonal of the earth installation and the volt metric probe
(terminal S, red wire) at a distance equal to about 0.5 times the diagonal of the earth
installation
¾ In the latter case several measurements shall be carried out moving the volt metric
probe back and forth (along the measurement direction) with respect to the middle
point and checking that the result is nearly constant.