Megger CM500 - Resistance and Continuity Testing

Operation (Contd.)
12
Setting A - MΩ and Ω, and Setting b
Determining Phase Sequence
When connected to all conductors of a three phase system, the
CM500 automatically displays the sequence of phase rotation.
Connect the
CM500 as follows:-
Line 1 Red phase Red lead
Line 2 Yellow phase Green lead
Line 3 Blue phase Black lead
If connected as above, the symbol is displayed when the
sequence is 1:2:3, or Red-Yellow-Blue. The symbol is
displayed when the sequence is 1:3:2, or Red-Blue-Yellow. If one
of the lines is faulty, neither of the symbols is displayed and the
normal ‘neon’ polarity indication is shown.
To measure the phase to phase voltages, the following switch
positions are used:-
Switch position Voltage Shown
(MΩ) L-PE Red and Green Leads V
1-2
(MΩ) L-N Red and Black leads V
1-3
(MΩ) N-PE Black and Green leads V
2-3
Continuity Testing, Low Resistance and kΩ Measurement
The CM500 will measure low resistance from 0.01Ω to 99.9Ω
and will automatically change range to kΩ up to 99.9 kΩ using
the 2-wire lead set. Up to 10 Ω of test lead resistance may be
subtracted using the test lead resistance nulling range.
Measurement is displayed on the large digital display, and the
analogue scale from 0 Ω to 20 Ω, or 0 to 20 kΩ.
In
Setting A, automatic polarity reversal is carried out with the
CM500 measuring resistance with both positive and negative
current flow. Normally the average of the two results will be
displayed.
Test Lead Resistance Nulling
The CM500 measures total resistance between its terminals,
including the resistance of the test leads. The value of the test
leads can be automatically nulled.
1. Firmly short the ends of the test leads together.
2. Select (Ω) lead resistance null position.
3. Press the
TEST key. The test leads are checked.
4.
0.00 Ω is displayed to confirm that a new lead value has
been stored.
CM500 will automatically display any voltage over 25 V
between the two test leads, and inhibit testing if >5 V.
Normal Supply
L-PE N-PE
L-N
Normal Supply
Neutral Live
Neutral
Open Circuit
Earth
Open Circuit