CHAPTER I 



TESTING FOR OPEN-CIRCUITS, SHORT- 

 CIRCUITS, POLARITY, AIR-GAP 



In the manufacture of armatures and fields for elec- 

 trical apparatus, possible defects in material and errors 

 of workmen can often be disclosed by what may be 

 termed "stationary testing." Defects and errors may 

 arise as follows: Through a wrong application of, or 

 mechanical faults in, insulation; the use of wrong material 

 for conductors, leads, etc. ; wrong assembly of connections 

 (workmen's mistakes). 



r?M I 



Fig. 1. Testing for Grounds 



Direct current armatures are tested for grounds, 

 short circuits, open circuits, and high resistance joints 

 before being sent to the Testing Department. In 

 testing for grounds a high potential is applied between 

 winding and core; the potential depending upon the 

 class of apparatus tested. When a ground develops 

 in test it can usually be located by smoking the insulation 

 at the breakdown point. 



If a low resistance ground has developed it may be 

 quickly and accurately located by the following method : 

 A low voltage current sufficient to give a readable 

 deflection on a galvanometer or millivoltmeter (Fig. 1) 



[5] 



