[Illustration: Fig. 707.--Watson field coils. Automatic machinery is employed to wind these coils; after winding, they are bound with tape, then baked to expel all moisture, and while hot, are saturated with an insulating compound and again baked for twelve hours to make them practically oil and water proof. Heavy flexible leads are brought out to avoid danger of breaking or other damage.] Cutting Out Damaged Armature Coils.--To cut out a damaged coil from an armature, first, disconnect the coil from the commutator, and after cutting off the leads, insulate the exposed parts with tape. Then connect the commutator bars (which were connected with the leads) with a wire of the same size as the wire winding. To remove the coil entirely, cut the band wire or remove the wedges, and lift up a sufficient number of leads and coils to permit of the removal of the damaged coil. Grounds in Armatures.--These faults occur when the armature coils become connected to the frame or core of the armature. When this grounding is confined to a single coil, it is not in itself liable to do damage. A simple method of locating a grounded coil is illustrated in fig. 708. [Illustration: Fig. 708.--Method of locating grounded armature coil. B is a battery or dynamo circuit giving a current of a few amperes through the armature by its own brushes (1 and 2). At G is placed a roughly made galvanometer, to carry some 25 amperes or so, one terminal being in connection with the shaft of the armature, and the other attached to a movable brush 3. Since the function of the particular galvanometer is simply to show a deflection when a current is passing, and to mark zero when there is none, a coil of thick wire with a pocket compass in the center will do all that is required, but care must be taken to remove it sufficiently far away from the disturbing effects of the armature magnetism. The manner of testing is as follows: Assume a steady current to be flowing from battery B through the armature; touch the commutator with brush 3, and a current will flow through G. Slowly rotate the armature or the brush 3 until the galvanometer G shows no deflection. The coil in contact with 3 will be found to be _grounded_. A hand regulator or rheostat R may be inserted in series with the battery or dynamo circuit to regulate the strength of the current passing.] Ques. What is the advantage of this test? Ans. The damaged coil can be located without unsoldering the coils from the commutator, which is sometimes a difficult operation without proper tools; further, the fault can frequently be repaired without disconnecting any of the wires if its exact position be determined.