When using a megger, how does an electrician confirm that the phase conductors are free from insulation damage?

When using a megohmmeter, commonly known as a megger, to assess the insulation integrity of phase conductors, the best practice is to check both phase-to-phase and phase-to-ground. This method allows the electrician to verify that the insulation between the conductors—both within a circuit and against ground—is intact.

By measuring phase-to-phase resistance, the electrician can confirm that there is no short circuit or breakdown between the different phases. Similarly, checking phase-to-ground ensures that the insulation is not compromised, meaning that there is no leakage current flowing to earth. This is crucial for safety and for the efficient operation of electrical systems, as insulation failure can lead to short circuits, electrical shocks, or equipment damage.

In contrast, measuring voltage drop across the phase conductors primarily assesses circuit performance during load conditions rather than insulation integrity. Visual inspection alone lacks the precision needed to detect microscopic faults in insulation. Lastly, using a clamp meter to measure current does not provide information about insulation condition; it only reflects the current flowing in the conductors, which is unrelated to insulation integrity.