Instructions

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[High Current] test instead of [No Trip] test, with the leads connected to the supply. In which case pressing
the [TEST] button will start a test.
Subsequent connection of test leads will run the AUTO START test.
AUTO START can be disabled in the SETUP procedure as described in section 8.
5.3.2 High current Phase to Neutral loop test
Repeat test 5.3.1 with the Green lead connected to the Neutral conductor.
This test can also be performed using the mains socket test lead, using the RED and BLUE connectors.
5.3.3 High current Phase to Phase loop test
Repeat test 5.3.1 with the Green lead connected to another phase conductor.
NOTE: Both the High current and No Trip loop tests will operate Phase to Phase.
5.4 High resolution loop test [High Resolut] (LTW425 only)
The [High Resolut] Loop test performs a 2-wire high current loop test, providing a loop test result to one
milliohm (0.001 Ω) resolution. This test is designed for non-RCD protected circuits.
A limited number of these tests can be done before the instrument will indicate
over-temperature, display the [hot] warning and inhibit further tests. In which
case leave the instrument to cool down for a few minutes.
5.4.1 All the high current tests in section 5.3 can be performed with the
instrument set to [High Resolut].
Note: In order to protect instrument from overheating, it is necessary to introduce pause time during testing
thus extending the [High Resolut] test to 15 seconds for measurements on supplies of less than 260 V
a.c. and 30 seconds for measurements on supplies above 260 V a.c.
5.5 Prospective Fault Current display [PFC]
NOTES:
The PSCC of a circuit is the largest Prospective Fault Current (PFC). In a single-phase system, this would
be the larger of the earth loop PFC and the neutral loop PSCC. In a multi-phase system phase-phase loops
also need to be considered and are measured in the same way as single-phase supplies.
PFC measurement accuracy
An accurate PFC measurement requires an accurate measurement of the loop resistance. The difference of
a few digits in the loop resistance measured will have a large effect on the PFC displayed.
Calculation of PFC (and PSCC) is based on the measured voltage divided by the measured loop resistance
(in ohms).
Measured Voltage
=
PFC
Loop resistance
The displayed value of PFC is calculated from the test results of voltage and resistance BEFORE they have
been rounded for display. Consequently the displayed PFC may not exactly correspond to the result of
manual calculation using displayed results of voltage and resistance.
5.5.1 PFC measurement
1. On completion of any loop test press the [PFC] key.
2. The prospective fault current is displayed in Amps.
3. Press [PFC] key again to return to loop impedance result.