Insulation Test Lock; Measurement Methods And Sources Of Error - Megger MFT1800 Series User Manual

6.2

Insulation test lock

To lock an insulation test ON, hold down either of the TEST buttons followed by either of the RED LOCK buttons.
To release the "Locked on" insulation test, press the TEST button.
WARNING : The test voltage will be permanently present on the test probes or crocodile clips when in the
locked position.
WARNING : Auto discharge - Auto discharge facility automatically and safely discharges the circuit at the
completion of an insulation test.
Live circuit warning – operates when connected to Live circuits > 25 V. Testing is still permitted.
Test inhibited – Live circuits greater than 50 V will inhibit testing.
6.3

Measurement methods and sources of error

Method of measurement
The selected DC test voltage (current limited to less than 2 mA DC).is applied to the circuit under test and the
resistance is calculated from measurements of the resulting voltage and current.
Capacitive circuits can take some time to charge. This is displayed as an increasing voltage that takes longer to reach
its maximum than normal.
The reading is stable with a circuit capacitance less than 5 μF.
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Insulation resistance
MFT1800 series 25