(6) Press the "Press to Test" button. The value of loop impedance will
be displayed with the appropriate units. A bleep will sound on
completion of the test.
For best results always test on the lowest possible range.
For example, a loop impedance measured on the 200Ω range may
give an indication of 0.3Ω whereas on the 20Ω range it may read
0.28Ω. In the event of the reading being in excess of the range (e.g.
more than 20 Ω on the 20Ω range) the appropriate over-range
symbol "OL" will appear on the display.
No harm will be done to the instrument by selecting too low a range.
#
CAUTION
● Even though the test current in the 2000 ohm range (15mA test
current) is low some RCD's, may trip due to sensitivity or where
there may already be additional leakage in the circuit being
tested.
The Loop impedance in a TN system is small and therefore it is
not recommended to test in the 2000 ohm range. RCD's will
have to be bridged to avoid tripping when using other test ranges.
● Meas
ured result may be influenced depending on the phase angle of
the distribution system when making measurement near a transformer
and the result may lower than the actual impedance value. Errors in
measured result are as follows.
System Phase
Difference
Error
(approx.)
10° -1.5%
20° -6%
30° -13%
5.3 Measurement of Prospective Short Circuit Current
－ (Models 4118A)
(1) Set the instrument to the 20kA range.
(2) Connect the test lead to the instrument.
(3) Attach the plug to the socket to be tested.
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