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This paper describes the shaft voltage reduction achieved by the brushless DC motor for air conditioning driven by the voltage source inverter. First, the simplified equivalent circuit of the concentrated winding brushless DC motor is derived based on the common mode equivalent circuit where stray capacitance is taken into account. Then, the electrostatic capacity distributions between winding and stator core, winding and magnet, stator core and magnet, and magnet capacitance are measured, and the shaft voltage is calculated with the simplified equivalent circuit. Finally, the bridge type equivalent circuit is derived, and it is confirmed with calculation and experiment that the shaft voltage can be suppressed when the inside and outside of the rotor core are insulated with resin (hereinafter, the insulated rotor).