CT-Operated Meter Billing Half the Real Consumption
An LT three-phase four-wire CT-operated energy meter serves a 55 kW flour mill. The CTs on site are nameplated 200/5 A, class 1. The meter display shows a programmed multiplier of '×20'. A departmental check meter (direct-connected, 3×10-60 A) is installed in series with the load for a 6-hour representative period and records 168 kWh. During the same 6 hours the consumer's meter register advances by 4.2 kWh. The consumer's monthly bills for the last six months have been between 2,100 and 2,200 units, against a connected load of 55 kW running roughly 6 hours a day for 26 days. The consumer has now received a notice proposing recovery for the past period and refuses to pay, saying the meter is the department's property and the fault is not his.
1. Calculate the correct multiplier, quantify the under-registration, and state the likely defect.
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Multiplier. A 200/5 CT has a ratio of 40, so the meter must be programmed with a multiplier of 40. It shows ×20, i.e. the CT ratio has been entered as though the CTs were 100/5.
Cross-check. Over the 6-hour check the direct check meter measured 168 kWh, so the average load was 168 / 6 = 28 kW. The consumer's register advanced 4.2 kWh in the same period, and 4.2 × 40 = 168 kWh - an exact match. That proves the meter, the CTs and the secondary wiring are all measuring correctly; only the multiplier stored in the meter is wrong.
Under-registration. The consumer is being billed 4.2 × 20 = 84 kWh for a period in which 168 kWh was consumed - a shortfall of 50%. Bills of about 2,150 units a month therefore correspond to roughly 4,300 units actually consumed.
Likely defect: a commissioning/programming error in the meter, not a CT or meter failure. The check also rules out a CT ratio mismatch - if mismatched CTs had been fitted, the register advance itself would have been wrong, not just the billing multiplier.
2. What would you verify on site before accepting that this is a programming error rather than theft or a CT fault?
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- CT nameplates on site: read ratio, class and VA on all three CTs, not the paper record. Confirm all are 200/5, of the same type, and that each is on the correct phase.
- Secondary wiring: look for shorting links left across a CT secondary, a reversed or open secondary, or any shunt/bypass across the meter current terminals. A shorting link left in place gives low current and is a classic tamper.
- Seals: meter and terminal-cover seals intact and matching the record; no sign of a drilled cover or magnetic influence.
- Meter data: read the CT ratio and multiplier pages as programmed, plus the event/tamper log, in the presence of the consumer or an independent witness.
- Register consistency: compare kWh with kVAh and with the maximum-demand register. A simple multiplier error scales everything proportionally, whereas tampering usually distorts one register or leaves a trace in the event log.
- Load survey: clamp primary and secondary currents simultaneously and confirm the ratio is really 40:1 under load.
Only when all of these are clean is the case closed as a programming error.
3. The consumer refuses any recovery. How do you handle it on the spot and what goes on record?
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- Do not argue about money at site, and do not change the meter setting yourself unless specifically authorised. A programming change made on the spot destroys the evidence and invites an allegation of tampering.
- Preserve evidence: photograph the CT nameplates, the meter display showing ×20, the seals and both readings; take a signed joint reading with the consumer; note the check-meter readings and the names of witnesses.
- Explain the finding plainly: the meter was measuring correctly but was programmed with a multiplier of 20 instead of 40, so only half the measured energy was billed. Say clearly that this is a departmental error, not the consumer's fault - that framing defuses the dispute.
- Report the same day in writing to the sub-divisional officer with the calculation, and let the competent authority decide the period and manner of recovery under the applicable regulation, normally by provisional bill after due notice. Do not promise or threaten a specific figure.
- Record: the defect, the probable start date (commissioning/installation date), the check results and the corrective action, so that the same programming error can be checked on every other CT meter in the subdivision.