Meters (Certification) Regulations (Northern Ireland) 1998

Conditions for all testing

5.—(1) The tests shall be carried out in accordance with Table 1.

Meter position

(2) The meter position requirement given in Table 1 applies to induction meters only. Tolerance applies to the vertical wall on which the meter base is mounted and a horizontal reference line or edge on the meter such as the lower edge of the terminal block.

Voltage and current supplies for polyphase meters

(3) (a) The order of the phases shall correspond to the sequence shown on the connection diagram.

(b) 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.

(c) The currents shall be balanced so that the current in any conductor shall not differ by more than 2.5% from the mean of these currents.

(d) 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

(4) 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 —

(a) 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;

(b) for 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

(5) Where all the errors of repaired 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 by more than 0.6% from the error obtained at the same load value by the Method B or Method C test.

Duration of test

(6) The tests described in paragraph 4 shall continue until the error of meters can be calculated within a tolerance not greater than ±0.2%.

Conditions for mixing methods of tests

(7) Method A tests may be used for intermediate and high loads, at unity and at 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.