Megger LCB2000/2 Guide De L'utilisateur page 21

Operation
Method of measurement
The phase-earth, phase-neutral or phase-phase loop
resistance can be measured. The instrument takes a
current from the supply and measures the difference
between the unloaded and loaded supply voltages.
From this difference it is possible to calculate the loop
resistance. The test current will vary from 15mA to 40A,
depending on supply voltage and the loop resistance
value. The test duration will depend on the loop
resistance value.
The Loop L-PE xtra range performs a test with acurrent
up to 25A flowing Line to Neutral and the resistance of
the source and line wires are measured. This is followed
by a current of 15mA flowing Line to Earth and the
resistance of the earth wires are measured.
Possible sources of error
The reading depends on a measurement of the supply
voltage and therefore noise or transients caused by
other equipment during the test could cause an error in
the reading. One way to check for these is to do two
tests and look for any difference in value. The
instrument will detect some sources of noise and warn
the user, where other instruments may give an incorrect
reading. Any leakage current as a consequence of other
appliances connected to the supply under test may
affect the reading. If the Phase-Earth loop is being
measured, this leakage may be due to filter capacitors,
etc.
20
RCD Testing
The instrument can test the operation of a variety of
types of Residual Current Devices (RCD), measure the
phase to earth loop resistance, and the contact voltage
of the installation. If Setting A (see page 5) is selected
when using the plug terminated lead set, the polarity of
the mains socket is immaterial. Line and Neutral will be
swapped if necessary, and an indication given on the
display. Setting b requires Line and Neutral to be fixed.
Pre-Test Configuration
Before performing an RCD test it is necessary to ensure
that the instrument is correctly configured for the rated
current and the specific type of RCD to be tested, and
for the type of test to be performed.
RCD Current Rating
From information given on the RCD to be tested, select
the RCD current rating on the rotary switch.
RCD VAR switch position
This position enables any RCD with a non standard
rated current between 10 mA and 1000 mA to be
tested. The test is performed at the selected current,
taking the 5I multiplier into consideration
1. Select (RCD) VAR.
2. Press the ENTER key twice to display the test
current.