540 ELECTRICAL EQUIPMENT 



assist in the choice of these and to explain the advantages gained 

 by using each particular instrument the information in the follow- 

 ing paragraphs will be found useful. 



For Direct-current Installations. Direct-current Ammeters. 

 (1) On machines of all kinds heating is the factor which deter- 

 mines the load which can be carried safely assuming the voltage 

 normal. Ammeters give an indication of the heating of circuits 



PlG. 344. Mississippi River Power Company. Chief Operator's Room 

 Showing Control Boards and Switchboards. 



in which they are connected and consequently are indispensable 

 for machine circuits. 



(2) They show the division of load between machines. 



(3) On feeder circuits they indicate which feeders are over- 

 loading the machines, and also furnish a means for indicating 

 the gradual growth or decline in the demands made upon the gen- 

 erating apparatus by any particular feeder, thus giving a warning 

 that the capacity of the apparatus must be changed, or the 

 feeder load rearranged. 



Direct-current Voltmeters. (1) They show that machines 

 are being operated at a voltage not too high to damage their 



