92 COMMERCIAL ELECTRICAL TESTING 



From these characteristics new ones should be plotted, 

 as shown in Fig. 29, the C~R being corrected for 75 deg. C. 

 rise, and the gear loss assumed as 5 per cent at full 

 load. If the gear loss derived from test has to be changed 

 at full load, it should be changed in the same ratio 

 throughout the curve. (See Table XI.) 



Cooling off tests are made by running the motor 

 under full load, with covers off, for one hour, shutting 

 down and reading temperatures as the machine cools 

 down. For the first hour after the machine is shut 

 down, the temperatures of the following parts are read 

 every fifteen minutes: armature, commutator, field, 

 frame, air in the motor, and room. After the first hour 

 temperatures should be taken every half hour until the 

 temperature of the hottest part is not more than 25 

 deg. C. above the surrounding atmosphere. 



The results of the cooling off test should be plotted 

 to time as abscissae and degree C. rise as ordinates. 

 The curves for armature, field, commutator, frame, 

 and air in the motor, should all be plotted on one curve 

 sheet. 



