A method of forming a motor winding wire for use in an oilfield application can include providing a conductive core; layering an insulating polymer layer about the core for electrical isolation thereof; adding an outer polymer layer about the insulating polymer layer to provide contaminant resistance; providing a sealable casing that comprises an oil-fillable space; disposing the motor winding wire within the oil-fillable space of the casing; filling the oil-fillable space with oil; and sealing the sealable casing to seal the oil in the oil-fillable space.