In a similar manner the dial shown in Fig. 253b may be read. In this case, however, three of the pointers rest nearly over the divisions and care must be used to follow the direction to avoid error. Commencing at the right, the first pointer indicates 7. The second pointer has passed 9 and is approaching 0. The third pointer appears to rest directly over 0, but since the second pointer reads but 9, the third cannot have completed its revolution and hence the figure last passed is set down which in this case is 9. Similarly, the fourth or left-hand pointer appears to rest directly over 1 but by referring to the pointer next to it on the right, we find that its indication is 9 as just explained. Therefore, the fourth pointer cannot have reached 1, and so the figure last passed which is 0 is set down, which in this case is 9. Similarly, the fourth or left-hand pointer appears to rest directly over 1, but by referring to the pointer next to it on the right we find that its indication is 9 as just explained. Therefore, the fourth pointer cannot have reached 1, and so we set down the figure last passed which is 0. The figures as they have been set down, therefore, are 0997, which indicates that 997 kilowatt-hours of electricity have been used.
If, for example, the reading of this meter for the preceding month was 976 kilowatt-hours, the number of kilowatt-hours used during that month would be 997-976 = 21 kilowatt-hours.
State Regulation of Meter Service.
—Electric wattmeters are subject to errors that may cause them to run either fast or slow. Complaints made of inaccurate records or readings are usually rectified by the electric company. In many States all public utilities are governed by laws that are formulated by public utilities commissions or other bodies from which may be obtained bulletins fully describing the conditions required of public service corporations or owners of public utilities. The following quotation from Bulletin No. V., 233 of the Railroad Commission of Wisconsin, will give an illustration of the requirement in that State.
Rule 14.—Creeping Meters.—No electric meter which registers upon “no load” shall be placed in service or allowed to remain in service.
This means that when no electricity is being used in the system the motor disc should remain stationary and if it shows any motion under such condition it is not recording accurately.
PERIODIC TESTS
Rule 17.—Each watt-hour meter shall be tested according to the following schedule and adjusted whenever it is found to be in error more than 1 per cent., the tests both before and after adjustment being made at approximately three-quarters and one-tenth of the rated capacity of the meter. Meters operated at low power-factor shall also be tested at approximately the minimum power-factor under which they will be required to operate. The tests shall be made by comparing the meter, while connected in its permanent position, on the consumer’s premises with approved, suitable standards, making at least two test runs at each load, of at least 30 seconds each, which agree within 1 per cent.
Single-phase, induction-type meters having current capacities not exceeding 50 amperes shall be tested at least once every 4 months and as much oftener as the results obtained shall warrant.