Quality is crafted into the Megger MJ159 (212159) Insulation Resistance Tester, which has excellent test voltage regulation, direct measurement readout and an external guard terminal to eliminate surface leakage current from the measurement. The MJ159 is a portable, self-contained instrument designed to give rapid and accurate measurements.

The MJ159 Insulation Resistance Tester features an analog display and has four selectable test voltages of 100, 250, 500 and 1000 VDC; measuring insulation resistance up to 2000 Megaohms; and a resistance range to 5000 ohms.

Power for the MJ159 is derived from a low-voltage, hand-cranked generator, which has been designed to be easy to turn even under full load conditions. The low-voltage generator is connected to an electronic inverter to provide a very stable test voltage. Accuracy of measurement is unaffected by variations in the generator cranking speed and the test voltage is maintained at its rated value.

As a safety feature, the AC voltage range becomes effective as soon as the MJ159 is connected to the circuit under test. Therefore, a warning is given that the circuit under test is not de-energized before the instrument is operated. Though calibrated for AC voltage, this range also monitors the automatic discharge feature so that after equipment having capacitance (i.e. a cable), has been tested, an indication can be given that the voltage has discharged to a level that is safe for removing the test leads.

The MJ159 Insulation Resistance Tester has a guard terminal which may be used to prevent the effects of surface leakage from influencing the readings. This is achieved by diverting the leakage current through the guard terminal and away from the instrument's measuring circuit. The tester is built into a strong ABS plastic case with a fold down carrying handle.