Possible Effects On Accuracy - Martindale Electric EZ165 Instruction Manual

Factors which should be considered are where equipment, such
as computers may introduce earth leakage currents due to internal
noise filter circuits. This earth leakage current can approach the trip
threshold of an RCD or RCBO, and the EZ165 test current will add
to it with the possibility of the protective device tripping.
Before using the EZ165 on critical circuits which supply computers,
medical equipment, or other systems where loss of supply is
unacceptable, ensure these are not being operated, in line with
normal practice when using electrical test equipment.
3.3.4 Possible Effects on Accuracy when Measuring Earth Loop
Impedance
Where supply circuits under test have highly inductive or capacitive
loads distributed on that circuit or there is an excessive amount of
mains disturbance present (e.g. motors running, etc) it is possible
the earth loop impedance measurement could be affected.
In such circumstances, where possible, disconnect any loads that
may be a source of error.
Alternatively, perform the measurement when the wiring under test
is electrically quiet.
The effect of highly inductive or capacitive loads and mains
disturbances can be to reduce accuracy on the lower two ranges,
e.g. if the actual loop impedance of the circuit under test is <1.7Ω
then the EZ165 may indicate in the range 1.7Ω to 5Ω.
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