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How do I test my system using a Megger (Mega-Ohmmeter)?

The megger is used as a quality control measure to test the insulation resistance.

Testing the insulation resistance detects any fault in the heater cable jacket. Such leaks cannot be spotted with a regular ohmmeter and help spot any damage to the cable and cable jacket.

The megger sends voltage through the cable to calculate the amount of current flowing through the cable jackets for an accurate indication of insulation integrity. Higher resistance means good insulation.

To Use:

  1. Make sure no power is running to the heating system you are testing.
  2. Insert the test probes into the L and E2 input terminals.
  3. Turn the dial to the 500V.
  4. Clip the black probe to the black wire coming from the heater cold tail lead.
  5. Clip the red probe to the ground wire.
  6. The display should show “- – – -” until the TEST button is pressed.
  7. Push and hold the TEST button to begin the test.
    • Please note: The number in the bottom right of the display screen shows the voltage being applied to the circuit. The resistance will show in the middle of the screen in MO or GO. The TEST icon will appear in the bottom right corner until the test is complete. If the resistance is higher than the maximum display range, the megger will display the > symbol on the left side of the screen. Higher resistance means good insulation. The minimum and maximum IR (insulation resistance) values can be found in the megger manual.
  8. Keep the probes connected and release the TEST button.
  9. Remove both probes and repeat the test by clipping the black probe to the red heating wire if testing a 240V system, or solid yellow if testing120Vsystem. Then repeat steps 5-8.
  10. Your reading should be higher than 1 mA. Anything lower, please call Warmup.

Please note, if the resistance (which should be greater than 1) is greater than 2000Mohms, the reading may not be displayed.

WARNING: HIGH VOLTAGE! Follow instructions and avoid direct contact with probes and wires during testing. High Voltage is being emitted and can cause injury or death. If unsure, contact a licensed electrician.


Further Questions?