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If a high level of electrical noise is detected the symbol [
] will be displayed. This indicates that excessive
noise was detected during the test. If this remains displayed at the end of the test it is recommended the test is
repeated.
5.1.1.3 High current test - (All instruments)
Performs a very fast loop test at a nominal 4A test current.
Description:
A resistive load (59
Ω
) is used to measure voltage drop and calculate the loop resistance. If the loop contains
inductance, the inductive reactance will be largely ignored. The loading current duration varies from 10
milliseconds to 640 milliseconds depending on the test condition.
When testing in close proximity to the sourcing transformer, a system phase angle of 18
°
will cause an additional
error of 5%.
5.1.1.4 High resolution test - (LTW425 only)
Performs a sequence of many high current loop tests to calculate a loop test result to three decimal
places.
Description:
Alternate voltage measurements on loaded and unloaded half cycles using a load resistor of approximately 59
Ω
,
as with the High Current test. The number of test cycles will be adjusted to obtain the optimum performance.
When testing in close proximity to the sourcing transformer, a system phase angle of 18
°
will cause an additional
error of 5%.
ALL TESTS WILL OPERATE PHASE TO EARTH, PHASE TO NEUTRAL AND PHASE TO PHASE.
NOTE:
THE LTW315 IS NOT RATED FOR PHASE TO PHASE MEASUREMENTS ON 240 VOLTS TO EARTH SYSTEMS
5.2 Performing a loop test
Note: Factory settings for the instrument are:
AUTO START
enabled
Mode 2 (extended testing) enabled
5.2.1 Non-tripping loop test [No Trip]
The [ No Trip] range is a 0,01
Ω
resolution, low test current earth loop resistance measurement.
5.2.2 No-trip testing using the mains socket test lead:
The instrument is supplied with AUTO START enabled, and in Test Mode 2, which will automatically extend a test
if noise is detected.
5.2.2.1 Phase to earth loop test
1. Select the [No Trip] test range on the lower range knob, and [Z] on the upper range knob where present.
2. Connect the RED plug of the mains socket test lead to the instrument.
3. Connect the GREEN plug of the mains socket test lead to the instrument.
4. Insert the plug into the mains outlet socket.
5. Ensure the supply voltage is displayed.
The loop test will automatically start and the [
] symbol will appear, and remain on, for the duration of
the test.
6. After a test period of 10 seconds the measured loop value is displayed and the [
] symbol will disappear.
To repeat the loop test press the [TEST] key.
The symbols [
] and [
] may appear during the test. Refer to section 5.1.1.2 (Symbols) for an explanation of
their meaning.
5.2.2.2 Phase to neutral loop test
Phase to Neutral testing can be made using the No-Trip test, as described above for the Phase to earth test.
However a High Current test will not trip RCDs when making a P-N test and it is recommended that a High
Current test is used for this measurement.
