In a method for applying an electrical insulation to a ferromagnetic body, provided with axial slots for receiving an electrical winding, of a primary element of an electrical machine, particularly to a slotted armature body of an armature of a direct-current motor, the body is coated with electrostatically charged plastic powder. For improving the economy of the method with a view to low system costs and great ease of maintenance while assuring reliable slot insulation, the coating is done with a high layer thickness by direct powder spraying onto the grounded body.