Megger LRCD200 series, User Manual

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14
Method of measurement
The plug ended test lead or 3 wire lead should be used for these
measurements. A constant current source is connected across the supply
and the time taken for the supply to trip is measured by the instrument in
milliseconds (ms).
The LRCD200, LRCD210 and LRCD220 - can perform the
following RCD tests:
Type
The RCD type is selectable from, AC, AC Selective, DC and
DC Selective.
1/2I
Non-tripping test at half the rated RCD trip current for 2
seconds, during which the RCD should not trip. (NOT
LRCD200)
I
Tripping test at the rated RCD trip current started on zero
crossing of the positive half cycle. The trip time will be
displayed
5I
Tripping test at 5 x the rated RCD trip current. The trip time
will be displayed in milliseconds. (NOT LRCD200)
0 or 180° Some RCDs are sensitive to the polarity of the supply, i.e
whether the test current is applied on the instantaneous
rising or falling part of the supply cycle. Tests should
therefore be performed at 0° and 180° and the maximum
time recorded.
Auto test Automatically tests 1/2I, I and 5I at 0º at 180º.
RampTest Used to check the trip current of an RCD.
RESIDUAL CURRENT DEVICE [RCD] TESTING
LRCD220:
If a voltage greater than 480 V is detected between phases the
display will show >480 V.
Over temperature
hot
To protect the instrument from over heating during Loop testing, thermal
protection is fitted. If the message [
hot
] appears in the display together
with the
G
symbol when loop testing, the instrument must be allowed
to cool down before further attempts are made at loop testing.
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.
Test results may be adversely affected by supply voltage fluctuations or
electrical ‘noise’ during a measurement. It is recommended that tests are
repeated and the results verified, if measurement results are considered
abnormal.
Errors can be reduced by:-
■
Use the 2 wire lead set with prods and making a firm connection to
clean conductors.
■
Make several tests and taking the average.
■
Ensure that potential sources of noise in the installation are isolated
(switched off), eg: automatically switched loads or motor controllers
■
Ensuring that the instrument is calibrated.