How to Measure Insulation Resistance with a Megohmmeter

1. Precautions for Using a Megohmmeter

① Handle the megohmmeter gently to avoid severe or prolonged vibration or flipping, which may damage the pointer shaft tip or bearings and reduce measurement sensitivity.

② When the pointer points to "0", do not forcefully crank the generator handle to prevent damage to internal coils.

③ After measurement, immediately discharge the tested object. Dingbo Power reminds: Do not touch the measured part or disconnect wires while the handle is still rotating or the object is not discharged to avoid electric shock.

④ Store the megohmmeter in a dry cabinet when not in use. Avoid extreme temperatures, humidity, dirt, or exposure to corrosive (acidic/alkaline) air/vapors, which may cause moisture absorption, mold growth, wire breakage, rust, or corrosion of internal coils, wiring, or parts.

2. Measurement Methods and Requirements

（1）Motor Status During Testing:

When measuring insulation resistance of motor windings, tests should be conducted under both actual cold and hot conditions. For inspection purposes, testing under actual cold conditions alone is acceptable.

（2）Measurement Procedures:

For motors with separate windings (e.g., stator windings, excitation windings of synchronous motors, or windings of reactors/current transformers in self-excited systems) where both terminals are exposed outside the motor housing: Measure insulation resistance of each winding to the housing and between windings. Non-tested windings must be reliably connected to the housing during testing.

For internally connected windings (e.g., three-phase windings connected in Y or Δ): Only measure insulation resistance from windings to the housing.

For hand-cranked megohmmeters: Maintain a rotation speed of approximately 120 r/min. Readings should be taken after the pointer stabilizes.

After measurement: Discharge the tested winding to the ground before disconnecting the test leads.

Since 1982, Dingbo Generator has been a generator set manufacturer qualified by the "National Internal Combustion Engine Quality Supervision and Inspection Center". The product quality has passed the IS09001 quality system standard certification. And obtained the qualification certificate for self-operated import and export. Over the years, Dingbo units have been widely used in all walks of life, and have won the network access qualification of the Ministry of Information Industry, the network access qualification of the Ministry of Radio and Television, the network access qualification of CNPC, the network access qualification of China Mobile, and the manufacturing qualification of marine units. In 2016, Dingbo was awarded the Certificate of Qualified Supplier of China Nuclear Power Group. Dingbo Generator has been cooperating with Shangchai Power for many years. In 2009, it became the OEM partner of Shangchai Power in China. Dingbo generator VOLVO unit ranks the top three in the Asia-Pacific sales volume, and is the core OEM partner of Sweden Volvo in the Asia-Pacific region. If any question please feel free to visit our website https://www.dieselgeneratortech.com/ or send email to [email protected].