Hi-I Line-Earth loop measurement takes 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 mains circuit to be slightly
attenuated due to the effective source impedance.
c) The tester measures a second half-cycle with the mains 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 ZI is calculated from the 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.
17
EETTHHOOSS 88440000
INSTRUCTION MANUAL
16
EETTHHOOSS 88440000
INSTRUCTION MANUAL
Principle of Measurement – No-Trip
The No-Trip Line-Earth loop range measures the same circuit value ZI using a two-stage
technique.
In the first stage the Live-Neutral loop impedance ZLN is measured using the same principle as
for Live-Earth loop.
The second stage is similar to Hi-I but operates at a low current to avoid tripping RCDs
CAUTION
Although fully protected against over voltage to 550VAC this tester should only be used
on a 230V supply.
Important note for calibration check box users: The smart loop test system used by the
Ethos 8400 is immune to sudden high value changes such as voltage spikes. As a result
when changing calibration or check box loop values the tester or the supply must be
switched off between changes of calibration values.
The Ethos 8400 Loop test function has 2 modes for Loop testing that allow the user to
conduct the most accurate test possible whether or not the circuit under test is
protected by an RCD.
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The Ethos 8400 is designed for a large number of loop tests in rapid succession. In the unlikely
condition this limit is exceeded a thermometer will be shown on the display until the unit cools
down.Testing will be inhibited while the thermometer is shown.
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Principle of Measurement – Hi-I
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