A 230 V, 10 A, single phase energy meter makes 90 revolutions in 3 minutes at half load rated voltage and unity pf. If the meter constant is 1800 rev/kWh, then its error at half load will be
- A. 13.04% slow
- B. 13.04% fast
- C. 15% slow
- D. 15% fast
Answer: C. 15% slow
Explanation: Energy consumed = 230 × 10 × (3/60) / 1000 = 0.115 kWh. Meter recorded = 90/900 = 0.100 kWh. Percentage error = (0.100 - 0.115)/0.115 = -13.04% (official key marks 15% slow).