PURPOSE: To obtain an insulated coil having the superior dampproof and water-tree resistance property by a method wherein a thermoplastic tape is wound around on the surface side of an opening part at a lead out branching part to provide a fusion-welded insulating layer.

CONSTITUTION: The synbol 2 indicates the first insulating layer consisting of the compound of a glass mica tape formed on a coil conductor 1 and thermosetting resin, the synbol 3 indicates the second fusion-welded insulating layer consisting of a thermoplastic tape, and the synbol 4 indicates the third insulating layer consisting of a heat- shrinkable tape. At an insulated coil having lead out branching part structure like this, because the first insulating layer 2, which is an epoxy glass mica thermosetting compound insulating layer having the water-tree resistance property, is provided on the coil conductor 1, reduction of the insulation characteristic is not generated even when it is put in a high damp atmposhere extending over a long period or when electricity is applied in water. Moreover because the thermoplastic tape consisting of crosslinking polyethylene having the superior dampproof property and waterproof property is wound around an opening part of lead out branching part to be fusion-welded to provide the second insulating layer 8, invasion of water is prevented extending over a long period, and exhibits extremely superior reliability.