EXTECH MG325 [12/18] Insulation resistance measurements

12 MG325-en-GB_v1.1 3/16

6.9 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 auxiliary

display.

3. Press the TEST button on the meter (or on

the test leads, if using the test lead with the

TEST button) 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 auxiliary display, the

symbol will flash and the front panel red LED will light. While the test is running, press

to change the test voltage display in the auxiliary display to the measured leakage current

display.

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

to store the reading

11. Use the SETUP mode to fine tune test voltage, set the default test time, and set a comparator

reference value. See the SETUP mode section for more details.

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 “>25V”, the

symbol will flash, and the buzzer will sound). If the circuit

under test is not live or if 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.