As the coil is being wound it should be occasionally tested for "grounds." A simple way of doing this is shown in Fig. 49. This consists of a cell of dry battery con

FIRST COIL COMPLETED

TESTING FOR GROUNDS

FIG. 49.-Testing for Grounds and Short Circuits.

nected in series with a galvanometer. An electric bell can be used instead of a galvanometer if desired.

The loose ends of the wires are bared of insulation. These being touched together, the circuit is closed and a current passes through the galvanometer and its needle is deflected.

If one of the wires is applied to the armature shaft and the other wire touched to the bared end of the coil wire, there should be no deflection of the galvanometer needle. Should the needle deflect, however, it will indicate that the wire of the coil is grounded on the iron of the armature. In that case the coil will need to be unwound until the spot is found and remedied.

When the coil is completed, with the sixteen turns of

wire, insert one of the half-round wedges in the slot with the outside end of the wire. Cut off the wire, leaving about 1 inches projecting from the slot. These ends of the coil must be marked for identification as it is of the utmost importance to be able to distinguish the outside and inside ends in order to connect them to the proper segments of the commutator.

A simple and effectual way to do this is to turn

a round loop in the outside end of the coil. This will represent "O" for the "Outside" end of the coil. The other end of the wire can have a small piece bent off at right angles to represent the letter "I" for "Inside" end.

In Fig. 50 is shown the first coil wound and the ends marked for identification.

The next cut, Fig. 51, shows the second coil which,

referring again to Fig. 47, passes through slot 2 and returns through slot 6.

In Fig. 52 the third coil is shown completed. This passes through slot 3 and returns through slot 7.

In addition to testing the coils for grounds it is also advisable to test for short circuits between the coils, as it sometimes happens that at the points where the wires of two coils cross each other on the ends of the armature,

they may be pressed so hard together that the insulation is injured and a short circuit results.

On the completion of the fourth coil, Fig. 53, all the slots contain sixteen turns of wire and are half filled. This shows, on one side, four outside ends, and on the opposite half, four inside ends. This coil passes through

slot 4 and returns through slot 8.

The next one, Fig. 54, is placed in the same slots as

coil 1, but is just the reverse, as its inside end is at slot 5 and the outside end at slot 1. Slots 1 and 5 will each have both an outside and an inside wire projecting as shown. On winding this coil, as well as those which follow, the under coils must be again carefully tested for grounds as it frequently happens that in winding these outer coils they will press down the underlying coils to such an extent as to break the insulation of the wire and cause

a ground on the armature or a short circuit between two of the coils where they cross at the armature ends.

It is sometimes necessary to unwind several coils to remedy such a defect.

When this fifth coil has been completed it will be at once apparent to the operator why it was so essential to mark the coil ends for identification, for if the work is examined at this stage of the winding only the outside

end of coil 5 could be properly identified were they not marked for that purpose.

Coil 6, Fig. 55, begins in slot 6 and returns through slot 2.

The seventh coil, Fig. 56, starts in slot 7 and returns. through slot 3.

It will be noticed that as the winding progresses the wire builds out into a hemispherical shape at the armature