334 



ARMATURE CONSTRUCTION 



as well as to the finished armature. During winding, tests should 

 continually be made for short circuits in the winding or faults to 

 the frame. 



The most convenient idea for this is the "lamp-test," which 

 consists simply of detecting continuity of any circuit by putting 

 it in series with a lamp, as outlined in Fig. 415. The lamp is 

 fixed where it is visible from the winding bench, and a pair of 

 loose wires a and b are accessible to the job. 



To test if there is continuity through a coil (which is im- 



FIG. 415. Lamp Test for 

 Short Circuits. 



FIG. 416. Transformer for Testing 

 Form -wound Coils. 



portant in the case of small wires which may get broken during 

 winding) the ends a and b are put on the terminals S and T of the 

 coil, and the lamp will light if the current is not broken. 



To test if the winding has gone to frame by damaged insulation, 

 one wire from the lamp circuit (a) is connected to one terminal of 

 the winding and the other (&) put on the iron of the armature. If 

 there is a fault the lamp will light, and if this is done on each coil 

 individually after it is wound, a fault is at once located and the 

 damaged coil can be at once rewound. 



Instead of a lamp a bell circuit could be, and often is, used. 



It is desirable with alternating windings to ohmmeter each 

 coil after winding. 



Form- wound coils should be tested individually, and a testing 



