Residential bill computation, register selection and an 'empty house' consumption complaint
A residential consumer in Thane has a single-phase direct-connected static meter showing 004876 kWh. The previous bill was raised on a reading of 004521 kWh. The meter also has a second register showing 004990 kVAh, and a display field showing MD 4.2 kW. The tariff printed on the bill is: fixed charge Rs 110 per month; energy charges on monthly slabs of 0-100 units at Rs 3.60, 101-300 units at Rs 6.85, 301-500 units at Rs 9.90 and above 500 units at Rs 12.10; meter rent Rs 20 per month; electricity duty 16 percent of energy charges only; late payment charge 1.25 percent per month, pro-rata, on the billed amount if paid after the due date. The bill is dated the 5th and due on the 20th. The consumer says the house was locked for 15 days during the month, yet the meter advanced by about 60 units in that period, and he intends to pay on the 30th.
1. Compute the consumer's bill for the month, showing the slab-wise working, and then compute the amount payable if he pays on the 30th.
Read the worked answer
Step 1: consumption 004876 - 004521 = 355 units.
Step 2: slab-wise energy charges
- First 100 units at Rs 3.60 = Rs 360.00
- Next 200 units (101-300) at Rs 6.85 = Rs 1370.00
- Remaining 55 units (301-355) at Rs 9.90 = Rs 544.50
- Energy charges = Rs 2274.50
Note the reasoning: slabs are applied progressively to the units lying inside each band, not to the whole 355 units at one rate. Applying Rs 9.90 to all 355 units would overcharge by a large margin and is a common trainee error.
Step 3: duty, fixed charges, meter rent
- Electricity duty at 16 percent of energy charges only = 0.16 x 2274.50 = Rs 363.92
- Fixed charge = Rs 110.00
- Meter rent = Rs 20.00
- Total = 2274.50 + 363.92 + 110.00 + 20.00 = Rs 2768.42, rounded to Rs 2768.
Step 4: late payment charge Due date 20th, payment on 30th = 10 days late. LPC = 2768.42 x 1.25/100 x 10/30 = 2768.42 x 0.0041667 = Rs 11.54.
Amount payable = 2768.42 + 11.54 = Rs 2779.96, i.e. about Rs 2780.
Sanity check: the effective rate is about Rs 7.8 per unit including fixed charges and duty, which is plausible for a residential slab bill of this size.
2. The consumer asks which register his bill uses and what the other two numbers mean. Explain, stating what would change if this were an LT industrial connection and what the multiplying factor is.
Read the worked answer
Which register is billed For a residential single-phase connection the bill is raised on the kWh (active energy) register, so 4876 kWh is the correct reading and 355 units is the correct consumption.
What the other fields mean
- kVAh = 4990: apparent-energy register. It records active plus reactive energy and is used where the tariff has a power-factor incentive or penalty, typically LT industrial and commercial categories, not residential.
- MD 4.2 kW: maximum demand, the highest average demand recorded in the demand interval during the month. For residential slabs it is informational only; for demand-billed categories it attracts a demand charge per kVA or kW, so it must be recorded every month.
Multiplying factor This is a direct-connected whole-current meter with no CT or PT, so the multiplying factor is 1: billed units = displayed units. A CT-operated meter would carry a factor equal to the CT ratio (for example 100/5 = 20) unless the ratio is programmed into the meter, in which case the display is already primary energy and the factor is again 1. Always confirm from the bill or the meter record which convention applies, because a factor of 20 applied twice, or not at all, produces a bill that is wrong by a factor of 20.
If this were an LT industrial connection
- Billing would typically be on kVAh (or kWh with a power-factor penalty/incentive), the MD would be billed, and the consumer would have an interest in maintaining a high power factor - which is exactly why the kVAh register exists. The same physical meter could serve either category, but the billing engine and the register selection would differ.
3. The consumer claims about 60 units were recorded in 15 days while the house was locked. Assess whether the figure is plausible and describe the checks you would carry out before accepting or rejecting the complaint.
Read the worked answer
Convert the complaint into a power figure 60 units in 15 days = 4 units per day = 4000 Wh per 24 h = about 167 W continuous. That is the equivalent of one small appliance running non-stop, or several appliances left in standby.
Is it plausible? Yes, it is entirely plausible if any of these were left on:
- a refrigerator (typically 0.8-1.5 units a day) plus router, TV standby, set-top box and inverter charger;
- a water pump on automatic control cycling on a float switch;
- a geyser with a failed thermostat, which can easily add 2-3 units a day;
- a shared connection or a neighbour's load tapped after the meter.
Checks before accepting or rejecting
- Is the meter recording with the main switch off? Switch off the consumer's main switch, note the reading and pulse count, and observe for 30-60 minutes. If pulses continue, load is connected ahead of the main switch, or the meter is creeping.
- Known-load field test: switch on a 1.5 kW heater for exactly one hour and confirm the meter advances about 1.5 units. This checks the meter constant and eliminates a misread register.
- Reading accuracy: verify the reading was actually taken (not estimated or averaged) and that the right register and decimal places were recorded; a one-digit misread explains many 'impossible' bills.
- Bill history: compare with the same month last year and the three preceding months; check for arrears, security-deposit adjustment, duty change or a category change bundled into the bill.
- Load audit: list appliances, ratings, hours of use and any appliances that remain energised when the house is locked.
- Leakage test: insulation resistance of the wiring and a check of the earth leakage path; current leaking to earth is real energy and is correctly recorded by the meter.
Likely conclusion: 167 W is small enough to be genuine standby and refrigeration load, so the complaint should be answered with the load audit rather than immediately declared a meter fault. If the main-switch-off test still shows pulses, escalate to a full meter test and an inspection for an unauthorised tap.