Measuring The "R Loop" Resistance - Metrix MX 435D Notice De Fonctionnement

Chapter II
Checking the measurement:
7. Note the measurement value previously obtained.
8. Starting from the initial position of rod S, move it towards H, then towards E, over a
distance of 10% of "d". Measure the earth resistance each time and note the results.
9. If all 3 values are identical or very close, the measurement is correct. Otherwise,
increase distance "d" and repeat the operation.
Remember to reconnect the earth terminal strip once you have finished
measuring !
In the event of accidental connection of earth measurement terminals to an AC voltage, the
instrument is protected up to 480 Vrms.
The instrument returns to normal working conditions in less than 1 min.
If an "I" is displayed when making a measurement using the 2000 Ω calibration, it means
that the earth resistance is greater than 2000 Ω and is therefore considered to be bad if the
installation is not protected by a 30 mA ground fault circuit breaker.
As indicated by NFC 15-100, in a TT configuration, the value of the earth resistance must
correspond to the sensitivity of the ground fault circuit breaker placed at the entry to the
installation such that: I∆n ≤ 50 / R earth.
Therefore for the standard ground fault value of 500mA, the earth terminal must have
Ω Ω Ω Ω
a resistance < 100 to make the evacuation of ground faults possible (cf. table
below):
3.3.

Measuring the "R loop" resistance

This measurement indicates the value of R N, PE resistance. This is an effective means of
checking the quality of an earth connection if it is not possible to measure the earth
(measure by excess).
Method whatever the type of measurement selected :
1. Select the "2000 " then "R loop 20 " position to refine the measurement. Connect
the MX 435D to a power supply using the accessories provided for this purpose.
2. Connect the MX 435D to a power outlet using the supplied accessory.
3. Press the "TEST" pushbutton.
4. Keep it pressed down until the measurement becomes stable.
Do not release the "TEST" pushbutton. The result is valid as long as
this button is pressed down.
5. Modify the full-scale range - if applicable (R > 20 ) or (R < 20 ) - and press
"TEST" again.
An excessive difference in N, PE potential can cause an error in measurement for VN,
PE > 50 Veff.
Digital Earth Tester
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