83 Ill. Adm. Code 460.370
Meter Accuracy Requirements
Section 460
Section 460.370 Meter
Accuracy Requirements
a) The accuracy of service watt-hour meters shall be determined
using the following criteria:
1) Light Load test: 10% of test amps at 100% power factor;
2) Heavy Load test: 100% of test amps at 100% power factor; and
3) Power Factor test: 100% of test amps at 50% lagging power
factor. The power factor test is only required on meter shop tests.
b) Accuracy limits:
1) On any test of a service watt-hour meter, the meter shall be
left so adjusted that the error shall not be in excess of the following:
A) Average error: 1% fast or slow.
B) Error at heavy load: 1% fast or slow.
C) Error at light load: 1% fast or slow.
D) Error at power factor: 2% fast or slow.
2) Meters shall not be deliberately set in error by any amount.
c) Each MSP shall test a service watt-hour meter for creep at the
time it makes any accuracy test of that meter if the percent registration at
light load deviates by greater than 2% from the percent registration at heavy
load. No service watt-hour meter found to creep shall be placed in service or
allowed to remain in service in that condition.
d) The average percent registration of a watt-hour meter shall be
determined by adding the light load registration to four times the heavy load
registration and dividing that quantity by five.
e) Demand meters, when tested on the loads specified in this
Section, shall be adjusted, if necessary, to meet the following requirements:
1) Demand Meters other than Lagged Demand Meters:
A) Electrical element – Error shall not exceed that specified for
service watt-hour meters in this Section.
B) Timing element – When used to measure time interval only, error
shall not exceed 2%. When used also to keep a record of time of day at which
the demand occurs, error shall not exceed 0.25%.
2) An MSP shall not install, provide, or maintain lagged demand
meters in this State.