HT instruments M71 - Manual (Page 12)

M71
EN – 11
¾ Only in case of a TT system a neutral conductor can be used as auxiliary earth rod
(see Fig. 4).
CAUTION
The instrument displays the sum value of R
A
+R
T
as result. Therefore the
measurement achieved is:
¾
The closer to R
A
(prospective value) the more negligible the value R
T
of the
auxiliary earth rod with respect to R
A
itself
¾ Increased “for the sake of safety” by R
T
that is to say if the value of R
A
+R
T
results to be coordinated with protective conductors, it will be far more
coordinated than that thanks to R
A
.
1. Press the instrument's start key.
2. Select function EARTH 2W pressing the left arrow key.
3. AUTO
If the circuit under test is assumed to be affected by electric noise press the
AUTO key to select the corresponding mode.
4.
Connect the red cable and the green cable into the corresponding instrument's input
terminals.
5. Connect the crocodiles to the test leads.
6. When necessary (symbol CAL missing or use of a new set of cables) carry out zero setting
of cable resistance (see § 4.3.1)
7. Connect the instrument's terminals to the circuit under test (see Fig. 4 and Fig. 3).
8. GO Press GO key to start measurement.
9. Display example of earth resistance
and disruptive voltage measured
values.
Should disruptive voltage have been
higher than 0.5V, it would be advisable
to start AUTO mode and repeat
measurement.
Value measured for
earth resistance
R
A
+R
T
Value measured for
disruptive voltage