BROWN
GREEN (PE)
v
Loop Impedance Testing
Principle of Measurement
ZI
Hi-I Line-Earth Loop Measurement Place in several steps:
a) The tester measures an unloaded half-cycle of the mains.
b) The tester switches in load RL. This causes the main circuit to be slightly attenvated
due to the eective source impedance.
c) The tester measures a second half-cycle with the main still loaded.
d) The load is removed.
The resistive part of ZI is calculated from the unloaded and loaded half-cycle measurements.
Each pair of measurements is taken adjacently to minimize noise and several such pairs may be
used for best accuracy.
The inductive part of the ZI is calcualted from unloaded and loaded half-cycle durations. Any
inductance causes a measurable lag in the loaded half-cycle.
NOTE: When testing on a supply with inductance exceeding 1mH or phase angle exceeding 30°
accuracy may be reduced.
VLE
T 2T 3T
T= 1/(2F)
16
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