NF EN 60521 : 1995

Explanatory foreword in relation to Class 0.5 meters
Clause
1. Scope
2. Units
3. Definitions
4. Classification
5. Mechanical requirements
6. Electrical requirements
7. Marking of Meters
8. Accuracy
9. Starting and running with no-load
10. Adjustment
APPENDIX A - Graphical symbols for watthour meters
Annex ZA (normative) Other international publications
                     quoted in this standard with the
                     relevant publications
Annex ZB (normative) Special national conditions
TABLES
    I. Clearances and creepage distances
   II. Standard basic currents
  III. Standard reference voltages
   IV. Power loss
    V. Apparent power loss
   VI. Heating
  VII. A.C. Voltage tests
 VIII. Voltage marking
   IX. Voltage and current balance
    X. Reference conditions
   XI. Percentage error limits (single-phase meters and
       polyphase meters balanced loads)
  XII. Percentage error limits (polyphase meters carrying
       a single-phase load, but with balanced polyphase
       voltages applied to voltage circuits)
 XIII. Interpretation of test results
  XIV. Temperature coefficient
   XV. Influence quantities
  XVI. Variations due to short-time overcurrents
 XVII. Variations due to self-heating
XVIII. Starting currents
  XIX. Minimum range of adjustment

Applies to newly manufactured induction-type watthour meters of accuracy Classes 0.5, 1 and 2, for the measurement of alternating current electrical active energy of a frequency in the range 45 Hz to 65 Hz. Applies to the assembly of meters and accessories, including current transformers, when enclosed in the metercase. Does not apply to any kind of measuring device.