Paragraph 5 Conditions for testing
The tests shall be carried out in accordance with Table 1 below.
Ambient temperature
Tests may be carried out at a temperature outside the temperature range given in Table 1, but within the range 15°C to 30°C, providing a correction is made in relation to the reference temperature by using the mean temperature co-efficient of the meters under test and of the working standard meter(s) used for determining meter errors.
Meter position
Meter position requirements given in Table 1 applies to induction meters only. Tolerance applies to vertical wall on which the meter base is mounted and a horizontal reference line or edge on the meter e.g. lower edge of the terminal block.
Voltage and current supplies for polyphase meters
The order of the phases shall correspond to the direct sequence shown on the connection diagram.
The voltages shall be balanced so that the voltage between any line and neutral or between any two lines shall not differ by more than 1.5% from the mean of the corresponding voltages.
The currents shall be balanced so that the currents in the conductors shall not differ by more than 2.5% from the mean of these currents.
The phase displacement between the current and corresponding phase to neutral voltage shall not differ from other current and voltage phase displacements by more than 3° at any power factor under any specified load conditions.
External magnetic induction
The test given in Table 1 in respect of external magnetic induction shall be carried out during commissioning or after major modification or refurbishing of a meter testing system. The test consists of determining the errors at 0.1Ib unity power factor with the meters normally connected and then determining the errors for:
single phase meters after reversing both current and voltage connections, for which half the difference between the two errors is the value of the variation.
polyphase meters by making two additional measurements after each of the connections to the current circuits and to the voltage circuits are changed over 120° but with the phase sequence unaltered, for which the greatest difference between each error determined and the mean of the three errors is the value of the variation.
Dial tests
Where all the errors of meters are determined by Method B or Method C test, an additional test in accordance with Method A shall be carried out. The Method A test shall be carried out at one of the loads used for the Method B or Method C test. The error obtained by the Method A test shall not differ from the error obtained by the Method B or Method C test, at the same load value as the Method A test, by more than 0.6%.
Duration of test
For any of the above methods of test, the duration of the test shall continue until the error of meters to be calculated within a tolerance of not greater than ±0.2%.
Conditions for mixing methods of test
Method A tests may be used for intermediate and high loads, at unity and 0.5 power factor, and Method B or Method C tests for the low load, provided that an additional Method B or Method C test is carried out at one of the test load values used for the Method A tests.