—
18
—
resistor will overheat. When this happens, further tests are automatically
inhibited and the over-temperature symbol (
) appears in the display. The
instrument must then be left to cool down, when testing may be resumed.
6.4
The loop impedance test
Since the earth fault loop is made up of conducting path which includes the
supply system back to the supply transformer, it follows that loop testing can
only be carried out after the mains supply has been connected. In many cases,
any RCD in the circuit will be tripped by this test, which draws current from the
phase and returns it through the earth system. The RCD 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
LED is lit do not proceed.
1
．
Press the test button once. Then, the instrument switches on.
2
．
Set the instrument to loop test 20
Ω
range.
3
．
If testing sockets, connect the plug lead to the Model 6010A and push the
moulded plug into the socket to be tested (see Fig 9).
4
．
Check the wiring lamps are lit (see above).
5
．
Note the mains voltage displayed by the instrument.
6
．
Press the
“
Press to test
”
button. The value of the measured loop
impedance will be displayed with the appropriate units.
7
．
If testing lighting or other circuits, connect the three-wire lead OMA DIEC to
Model 6010A, 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).
8
．
If any RCD associated with the circuit trips out, reset the RCD and try
testing again, this time operating the phase selector switch once prior to
pressing the test button. This will change the period of the waveform over
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