Metering, Energy Accounting and Consumer Installation
This domain tests consumer metering and the commercial side of distribution: meter types, CT-operated meters, meter constants, reading and billing, consumer installation checks, and energy accounting including distribution losses. Expect simple multiplier and loss calculations.
Core rules
- Direct-connected meters are used for small loads. CT-operated meters are used for larger loads; the meter reads secondary current, so the reading must be multiplied by the CT ratio.
- Multiplier = primary current / secondary current. For a 200/5 CT, multiplier = 40. Meter constant (imp/kWh or revolutions/kWh) is used in meter testing, not as the billing multiplier.
- A consumer installation includes service cable, meter, main switch, distribution board, MCBs or RCCB, and earthing. Polarity, phase sequence, neutral and earth continuity must be checked before energising.
- Energy accounting compares input energy at the feeder or DT with billed consumer energy. AT&C loss includes technical and commercial losses; a simple energy loss percentage = (input − billed)/input × 100.
Worked example
A consumer meter is connected through a 100/5 CT. The meter reading advances by 150 kWh in a month. Find the billed energy, and calculate the loss if the feeder input is 10,000 kWh and total billed energy is 8,500 kWh.
CT multiplier = 100/5 = 20. Billed energy = 150 × 20 = 3,000 kWh. Energy loss = (10,000 − 8,500)/10,000 × 100 = 15%. The meter itself records secondary energy; the multiplier converts it to primary energy. If the multiplier is forgotten, the consumer is billed one-twentieth of the correct energy.
Traps that cost marks
- Forgetting the CT multiplier or inverting the CT ratio.
- Confusing meter constant with CT multiplier.
- Reading a dial meter in the wrong direction or missing a full revolution.
- Mixing kWh and kVAh in tariff calculations.
- Treating all AT&C loss as theft; technical losses and metering errors also contribute.