Loop impedance
tests
18
will see this as the type of fault it is designed to protect against, and will
trip. To prevent this unwanted RCD tripping during loop testing, any RCD
must be taken out of circuit and temporarily replaced with a suitably rated
MCB unit. The RCD will need to be replaced after the loop test is
completed.
WARNING
Do not proceed with testing unless the P-E and P-N lamps are lit
to confirm that the wiring is correctly connected. Should these two
lamps not be lit, investigate the wiring connections of the
installation and rectify any faults before proceeding with the test.
If the red LED is lit do not proceed.
1
Set the instrument to loop test 20
Ω
range.
2
If testing sockets, connect the plug lead to the KT62 and push the
moulded plug into the socket to be tested (see Fig 9).
3
Check that the wiring lamps are lit Green (PE), Green (PN) and the
third red LED is OFF
4
Note the mains voltage displayed by the instrument.
5
Press the ‘Press to test’ button. The value of the measured loop
impedance will be displayed with the appropriate units. The test will
start at the sound of a bleep. Whilst the test is being conducted the
display will show a series of moving square symbols (see below). When
these stop the measurement value will be displayed.
6
If testing lighting or other circuits, connect the three-wire lead to the
KT62, connect the red (phase) lead to the phase connection of the
circuit under test, connect the black (neutral) lead to the neutral
connection of the circuit under test, and connect the earth lead to the
earth associated with the circuit. (see Fig 10).
7
The measuring ranges 200
Ω
and 2000
Ω
use a low test current.
Therefore it will be possible to carry out a loop impedance test in the
presence of RCD's rated at 30mA or above (assuming that there is no
other earth leakage on the circuit being tested). Note that readings
below 15
Ω
will be subject to significant variances due to the fact that
