R8‑11 METHOD OF DETERMING AVERAGE ERROR OF METERS
(a) In determining the average error of a watt hour meter, the following procedure is recommended:
(1) All meters whenever possible, shall be tested at the following three loads: one‑tenth of the current rating of the meter, normal load and at rating.
(2) The average of these tests obtained by multiplying the results of the test at normal load by three (3), adding the results of the tests at one‑tenth rating and at the current rating, and dividing the total by five, shall be deemed the condition of the meter.
(3) In an installation where it is impossible to obtain a load of ten percent (10%) of the rating, or one hundred percent (100%) of the rating of the meter tests shall be made at the nearest obtainable loads to ten percent (10%) and one hundred percent (100%) of the rating of the meter and the values given in the ratios as stated above.
(b) To determine normal load, use the percentage of connected load indicated below for the class of service metered.
Class of Service Metered Connected Load
Residence and Apartment Lighting 40%
Elevator Service 40%
Factories (Individual Drive), Churches and Offices 45%
Factories (Shaft Drive), Theatres, Clubs, Entrances,
Hallways, and General Store Lighting 60%
Restaurants, Pumps, Air Compressors, Ice Machines
and Moving Picture Theatres 70%
Signs and Window Lighting and Blowers 100%
(c) When a meter is connected to an installation consisting of two or more of the above classes of load, the normal load would be the sum of the normal loads for each class.