Instructions

The LTW325, LTW335 and LTW425 are able to derive the (R1+R2) circuit impedance from tests made on a

live installation. It is not possible to isolate R1 or R2 separately.

Application note for Zref and R1+R2 measurement:

On initial verification of a new electrical installation, the value for R1+R2 should be obtained by

continuity testing methods (dead testing) as per BS 7671:2001 or other international standards.

For periodic inspection reports (PIR) where it is not possible to isolate the supply, the user should first verify

the Circuit Protective Conductor (standard practice) prior to using the Zref and R1+R2 function on the

instrument.

Prior to measuring Zref, all main equipotential bonding must be in place.

Note: Measurements made on live installations by this method may be lower than the Ze + (R1+R2) from

those obtained by continuity testing methods, due the existence of parallel earth return paths from

extraneous conductive parts.

To make use of the R1+R2 test feature, the reference/distribution board (Ze or Zdb) result must be stored in

the instrument’s memory (Zref), prior to measuring R

+ R

5.8.1 Measuring Zref

1. Switch the top range knob to [Zref]. The display will show the [ ] symbol to indicate a Zref test

mode is selected.

2. Select any loop test range as appropriate.

3. Connect the instrument to the circuit under test as described in section 5.2, 5.3 or 5.4 as required.

4. Press the [TEST] button to perform a loop test. The test result is displayed and stored internally as

Zref.

5.8.2 Measuring R1+R2

5. Switch the top range knob to the [R1+R2] range. The display will show the [ ] symbol to

indicate an R1+R2 test mode is selected.

6. All subsequent loop test measurements will have the Zref resistance subtracted.

7. To view the stored value of Zref press the PFC key, press the PFC again to return to the R1+R2 value.

8. If measured value of R1+R2 is less than zero, the display will show the measured value of R1+R2 for 2

seconds, then the error message [ ] will be displayed to indicate such error. In which case

repeat the R1+R2 measurement. If the error persists, repeat with a new Zref measurement followed by

R1+R2.

If a Zref measurement was not made prior to an R1+R2 test, an R1+R2 test will not be performed, and the

warning [ ] will be displayed for 2 seconds.

6. Voltage and frequency measurement

WARNING: The instrument must not be used on CATII, CATIII or CATIV systems with

voltages greater than 300V phase to earth and 440V Phase to Phase.

6.1 Phase to Earth and Phase to Neutral voltage and frequency measurement

To measure the voltage of the electrical supply using the mains socket test lead:

1. Set the instrument to the [V/Hz] range.

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. The instrument will display the voltage and the frequency.