Chauvin Arnoux C.A 6456 Notice De Fonctionnement page 71

4.4 WIRE LOOP MEASUREMENT (Z LOOP)
4.4.1 DESCRIPTION OF THE FUNCTION
In a TT network, measurement of loop impedance LPE is a rapid and practical way of checking a earth
resistance without planting auxiliary rods. In this case, the measurement includes the earthing resistance
of the power supply transformer of the installation and the resistance of the distribution cables. It is therefore
a high earth measurement, and any error is on the safe side.
In TT and TN networks, this function can also be used to check and size the protective systems in place by
a rapid and easy measurement of the loop impedances between L and PE, L and N, and N and PE. This
function can also be used to calculate the corresponding short-circuit currents (sizing of fuses and circuit
breakers).
Note that the instrument allows measurement of loop impedance LPE behind 30mA circuit-breakers without
causing them to trip (principle patented by Chauvin Arnoux).
In an IT network, use the instrument's "ZLINE" function.
The measurement principle is the same as for an earth measurement in a live condition.
When the TEST key is pressed, the instrument :
- checks that the amplitude and frequency of the voltages present are correct,
- measures the voltage between the TEST key and terminal PE,
- interchanges L and N internally if the 2 conductors are reversed in the socket,
- generates a current (high or low according to the user's selection) between terminals L and PE,
- measures loop impedances Z
Note: the measurement of Z does not trip the earth fault breakers even with high currents.
LN
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, Z , et Z .
LN LPE NPE
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