Insulation Testing and High Resistance Measurement
The CM500 will test insulation resistance (1 kΩ to 99.9 MΩ)
between phase, neutral and earth (ground) as required, at the
selected voltage. With a default setting of 500 V d.c., the test
voltage can be altered to 250 V, 500 V or 1 kV as required.
Measurement is displayed on the large digital display and the
analogue scale.
2-wire lead set method
1. Disconnect Phase, Neutral and Earth at the distribution
board.
2. Connect the leads across the isolated circuit.
3. Select
(MΩ) L-N.
4. Press either the
I or the TYPE key to display the test
voltage. Press again until the required test voltage is
displayed.
5. Press and hold the
TEST key.
6. Circuit resistance value is displayed.
7. Release the
TEST key, but maintain connection to allow
the test voltage to discharge.
3-wire lead set method
Use of a 3-wire lead set enables all combinations of insulation to
be tested without changing lead connections.
1. Disconnect Phase, Neutral and Earth from the distribution
board.
2. Connect the red lead to Phase; the black lead to Neutral,
and the green lead to Earth (ground).
3. Select
(MΩ) L-PE, L-N or N-PE as required.
4. Press either the
I or the TYPE key to display the test
voltage. Press again until the required test voltage is
displayed.
5. Press and hold the
TEST key.
6. Circuit resistance value is displayed.
7. Release the
TEST button, but maintain connection to allow
the test voltage to discharge.
Power plug method
The insulation resistance of an installation may be tested by
using the plug terminated test lead at a convenient socket
outlet. However:-
a) The installation must be isolated from the supply.
b) The insulation test will incorporate the immediate
circuit and any other circuit connected on the load side
of the distribution board (D.B.).
c) If a low reading is obtained, each circuit must be
individually tested from the distribution board to locate
the fault.
Operation (Contd.)
14
After performing an insulation test, maintain
connection to the circuit under test to allow the circuit to
discharge. If voltage remains after a test, the
CM500
will normally display this as it is discharged. It must be
verified that the test voltage has been discharged
before moving onto the next test.
When using the 2-wire lead set to measure
insulation, always select (
MΩ) L-N. The insulation
will be measured between the two leads.
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