Megger LCB2000/2 Guide De L'utilisateur page 18

Operation - Loop Testing
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
large effect on the PFC displayed.
Errors can be reduced by:-
• Using the 3 wire lead set with prods and making a
firm connection to clean conductors.
• Making several tests and taking the average.
• Ensuring that potential sources of noise in the
installation are isolated (switched off), e.g.:
automatically switched loads or motor controllers
• Ensuring that the instrument is calibrated at the
appropriate intervals (12months recommended).
No trip loop-testing -
The LCB2000/2 ad LCB2500/2 have two loop
impedance ranges guaranteed not to trip any RCD rated
at 30mA or above - L-PE 0.1Ω and L-PE Xtra. These
ranges are denoted by the symbol on the range label.
L-PE 0.1Ω
(Use only where no neutral connection is available)
The Loop L-PE 0.1Ω range is a low test current,
(15mA), earth loop impedance measurement range.
This range has the advantage of only requiring two
connections to the circuit being tested and is useful
where a neutral is not available. Because the entire test
is conducted at low current, measurements can be
adversely effected by noise on the supply. For this
reason it is preferable to use the L-PE xtra range for all
instances where a connection to the neutral conductor is
possible. Tests may be made via installation sockets
with the plug terminated test lead, or at any other point
using either the 2 or 3-wire lead set. Connections are
required to Live and Earth only.
L-PE xtra (Use this range whenever a connection to
neutral is possible)
The Loop L-PE xtra range is a high resolution, (0,01Ω),
low test current earth loop resistance measurement
range. It requires a connection to neutral, but allows
quick and accurate measurement of the earth loop
resistance without tripping all RCDs with a rated
current 30mA or higher. During the L-PE xtra test the
instrument automatically gathers a considerable amount
of information regarding the circuit being tested along
with the loop impedance measurement. This
information, shown below is presented for viewing at the
end of the test.
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