Insulation Resistance Measurements - Extech Instruments MG320 User Manual

6.7 INSULATION RESISTANCE MEASUREMENTS

Note: Disconnect the unit under test from all power sources and isolate it from any stray
resistance.
1. Connect the red test lead to the meter's INSULATION (+) jack (7) and the black test lead to the
EARTH (-) jack (6). Connect the probe end of the test leads to the circuit under test.
2. Set the rotary function switch to one of the Insulation Resistance test positions (50V, 100V,
250V, 500V, or 1000V); the selected test voltage is indicated on the top right of the display.
3. Press the TEST button on the meter (or on the optional remote test lead) to start testing (TEST
will display).
4. The primary display and the analog bargraph will show
the insulation resistance in Ω.
5. The test voltage (VDC) value will be indicated in the top
right display, the
red LED will light.
6. The meter defaults to test lock mode (lock icon
displayed) so the test will run without having to hold the
TEST button.
7. Press the TEST button to stop the test.
8. At the end of each test the high voltage switches off
(alert symbol and LED light switch off), the measured
resistance value is held in the primary display, and the
meter internally discharges the balance of the test
voltage.
9. Short press the H (Hold) button to freeze (H icon) or
unfreeze (no H icon) the displayed reading.
10. Press
Note: If the circuit under test is live and has a voltage potential (AC/DC) over 25V, the meter will not
test (the display will show "EXT" and the
its voltage is less than 25V, the meter will begin applying voltage to the circuit under test.
Note: Do not turn the function switch to another test position during a test. Please wait until a test is
completed and test leads are removed from the device under test before moving the function switch.
6.7.1 Disable Insulation Test Lock Mode
To disable test lock mode, press and hold the
then press and hold the TEST button for the duration of the test (TEST will be displayed).
Release the button to stop the test.
symbol will flash and the front panel
to store the reading
symbol will flash). If the circuit under test is not live or if
button until the lock icon switches off and
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