Essential electrical tests to perform before powering up a newly rewound motor.

Never apply full mains voltage to a newly rewound motor without rigorous testing. A simple oversight can cause the new winding to immediately burn out.

Start with a Megger (insulation resistance) test. Apply 500V or 1000V DC between the copper phases and the iron chassis to ensure the slot insulation is perfectly intact. The reading should ideally be in the hundreds of mega-ohms.

Finally, use a low-resistance ohmmeter or milli-ohmmeter to check the phase balance. All three phases in an AC induction motor should have identical resistance down to the decimal. Any imbalance indicates a shorted turn or a miscounted coil.