How to calculate domestic power consumption? Fact File 24

Electronic Energy Meter (EEM) is used to meter the domestic power consumption for a prescribe period, say one month. The Electronic Energy Meter (EEM) functionally outperforms the traditional Ferrari’s wheel meter. The EEM has many advantages.

1. It reduces the cost of theft and corruption on electricity distribution network with electronic designs and prepayment interfaces.

2. Electronic energy meter measures current in both Phase and Neutral lines and calculate power consumption based on the larger of the two currents.

3. EEM improves the cost and quality of electricity distribution.

Most of the electric appliances consume large amount of current. Heater, Electric iron, Mixi, Grinder, Fridge etc are current hungry appliances. Their uncontrolled use will definitely increase the bill and may change the tariff. If these instruments are kept ON for many hours, your electricity bill will be really shocking. Old humming fan, CRT based TV, Fridge with defroster (its heater switches on frequently to melt the Ice.) etc can also increase the current consumption. Use of these high current devices during the peak hours (when voltage drops) will double the current consumption.

The EEM has a Imp / kWh LED which blinks to indicate Impulses per Kilo Watt Hour. Normally if a 100 watts bulb burns for 1 minute, the pulse rate of LED in the EEM will be 5.3 blinks per minute. + or – 5 times can be considered as normal. If the blinking rate is very high, your EEM is showing a wrong reading and you will be forced to pay more. It is very easy to monitor the power consumption and we can reduce the bill considerably. Remember! unlike mechanical meter, Electronic energy meter will sense very small amount of current. Even a glowing indicator lamp in the switch board will cost something.

Domestic power supply is 230 volts 50 kHz or 110V 60 Hz in some country. The current consumption depends on the Wattage of the instrument used. Current consumption can be calculated using the formula

I = W /V

I is the current in amperes, W is the wattage of instrument and V the 230 volt power supply.

For example a Compact Fluorescent Lamp (CFL) rated 11 watts consumes 0.04 ampere current in one hour at 230 volts.
Wattage of an instrument can be calculated using the formula

W= V x I

Let us see its working and method of calculating the domestic power consumption and some tips to reduce electricity bill.

On the front panel of EEM there will be 4 LED indications
Ǿ N OK LED ON Phase and Neutral OK

E / L LED OFF Earthing correct

LED ON Earth leakage and current loss

Imp / kWh LED Blinks Impulses per Kilo Watt Hour.

This LED is larger one.
How to Monitor the Electronic Energy Meter?

1. The first step to monitor the energy meter is counting of the LED pulses per unit (kWh). Usually the pulse rate will be 800 to 3600 imp/ kWh. Imp.3200 is the pulse rate of most EEMs. The pulse rate can be calculated by counting the blinking of LED.

2. Suppose the pulse rate is “X imp. / KWh”. (In most meters it is 3200 imp. / KWh). This indicates the pulse rate of LED if 1000 Watts / second is consumed in 1 hour.

3. Suppose a 100 watt bulb is switched on for 1 minute, the pulse rate will be “P”.

4. Then “P” can be calculated using the formula

P= X x100x60 / 1000×360

That is if 1000 watts is consumed for 3600 seconds the output pulse will be “X” per hour. So the pulse rate for 100 watts for 60 seconds is “P”.

So “P” (100 watt per minute) can be calculated as follows:-

P= X x 100 x 60 / 1000 x 3600

That is 3200(X) x 100 x 60 / 1000 x 3600 = 5.3 pulses / minute

Normally if a 100 watts bulb burns for 1 minute, the pulse rate of LED will be 5.3 blinks per minute. + or – 5 times can be considered as normal. If the blinking rate is very high, your EEM is showing a wrong reading and you are forced to pay more.

Get ready to check your EEM

1. Connect a 100 watt bulb in an outlet holder.

2. Switch off all the lights, fans and unplug all the electric appliances.

3. Check the meter. If the LED blinks, it indicates wiring defects and leakage.

4. Check the wiring and rectify the defect.

5. If the LED remains OFF, wiring is OK and meter is not sensing the current flow.

6. Switch on the 100 W bulb with the help of another person and count the LED blinks for 1 minute. + or – 5 times can be ignored.

7. Take the total count per minute. It is the pulse rate for a 100 watt bulb/ minute( “P”)

8. If “P” is very high or low (for a 3200 kWh meter) than the “P” already calculated as above, the meter is defective.

9. Report the matter to the Power company for meter observation.

Know your home appliances; they are current hungry.


Power rating of Household appliances

The ratings are average. This may change depending on the make

Some tips to make your appliances friendly and to save energy.

1. Check the domestic wiring periodically for leakage and current loss.

2. Install ELCB (Earth Leakage Circuit Breaker) which will immediately disconnect the power when it senses more than 40 milli ampere current through earth line.

3. Fridge is one of the current hungry appliances. Do not keep the door opened for more than 2 minutes. Do not keep hot food materials inside the fridge. Defrost weekly; otherwise current consumption will be more.

4. Do not keep TV or Computer in the standby mode for long periods. Switch off immediately after the use. Even in the standby mode these devices takes 10 watts or more power

5. Unplug all the instruments which are not using daily.

6. Make all the preparations before switching on the instruments like Washing machine, Mixi, Iron etc.

7. Use heater or water heater only in extreme cold conditions.

8. Restrict the use of Iron and use one with temperature regulator.

9. Overheating and humming from fans indicate defects which lead to over meter readings.

10. Switch off fans and lights after the use.

11. Do not charge UPS, Inverter or Emergency lamp battery continuously (If there is no cut off facility). It will consume more current as well as reduce the life of battery. One hour charging at an interval of two days is sufficient to keep the battery in top condition. Over charging will heat up the battery and reduce its life along with unnecessary power loss.

12. Keep the plugs and sockets clean to avoid sparking and power loss.

13. Avoid the use of Mixi, Heater, Iron etc during the peak hours from 6 pm to 10 pm.

14. Replace all the bulbs with Fluorescent lamps and low watt CFL

15. Use low wattage CFL lamps or LED Lamps in rooms or places where bright light is not required.

16. Do not charge Mobile phone daily. Equal charging and discharging will keep the battery in top condition. Charge the mobile phone only when the charge indicator shows 50% charge. Over charging will reduce the life of battery.

Electricity billing

Electricity billing is based on the usage of current by the domestic appliances. If a 1000 watts bulb burns for one hour, 1 unit current is used. Current consumption is calculated using the formula

Total Watts x 1 hour / 1000

For example, the total wattage of all the electric appliances used is 500 watts, the power consumption in one hour will be

500 x 1 / 1000 = 0.5 units

If the consumption per hour is 0.5 units and the appliances are used 8 hours per day, then the power consumption will be 4 units per day and 120 units per month.