468 



ELECTRICAL MEASUREMENTS 



rated full-load current, and at 10 per cent of rated full-load cur- 

 rent should register correctly to within 3 per cent. The light- 

 load adjustment must be such that the meter does not " creep," 

 that is, rotate continuously when the consumer is not using 

 energy. This should be true even when the supply voltage is 10 

 per cent higher than that at which the meter was adjusted. 

 Electrical supply companies which give careful attention to their 

 meters, instruct testers to leave them so adjusted that they regis- 

 ter correctly to within 1 per cent at from 5 to 10 per cent of full- 

 load and to within 1 per cent at full-load. 



The periodic service tests on a large distribution system where 

 careful attention is given to the upkeep of the meters may be 

 expected to show results comparable with the following: 



The tests were made at intervals of from six months to a year. 



The aim of careful supply companies is to so maintain their 

 meters that a full-load accuracy of 98 per cent or better is 

 obtained. 



The energy losses in the meter must be small, for the potential 

 coil of the instrument is in circuit continuously, even though the 

 consumer is using no energy. The expense of energizing the 

 potential coils falls on the supply company; in the aggregate it 

 may be a considerable item. 



