What is the basic difference between the working of old electromechanical meters and new electronic meters?  Why the utilities have switched over to new electronic meters when both are ISI marked?

There could be following reasons for inflated bills against the energy consumed:

1. New electronic meter installed at the residence is running fast.

2. New meter is working satisfactorily but the wiring to meter, which was done earlier as per old electromechanical meter, is not suitable for the new electronic meter.

3.  Reasons other than indicated at (a) & (b) above

4. There are no reasons as indicated above but for the fact that energy consumed by the consumer is actually high.

 There is a simple check we can perform to find out whether the problem is in the new electronic meter or in the connections or household wiring etc. Before moving further the connection diagram of electronic meter indicated under answer 4 needs to be referred to. As per this diagram, the current entering the meter through phase wire and coming out of the meter through neutral wire may be got checked from any qualified and experienced electrician. There could be any one of the following three observations of the electrician:

1. Incoming and outgoing current is almost the same. If such is the case, then it may be concluded that connection to the meters are ok and there may be some problem in the meter itself (see question 3 for details with regard working of electronic meter).

2. Outgoing current is appreciably more than the incoming current. If such is the case, then somebody else’s neutral wire has got connected to the meter’s neutral wire and it is because of this reason that the meter is running fast. To be doubly sure, the following additional spot checks may be carried out:

   1. Disconnect the neutral or switch off the MCB if it is installed in the neutral wire (load side). If the meter is still working, it means that there is an improper neutral connection

   2. Switch off all electrical points in the house (including LEDs and indicating lamps) and check if the meter is working.  If yes, then it means that there is an improper neutral connection. (See question 5 for details with regard to improper neutral connection.)
       

3. Outgoing current is less than the incoming current. If such is the case then it means that there is some leakage of current, earthing, etc in the building. This may be because of the old worn-out wiring in the house. To be doubly sure, following additional spot check may be carried out:

   1. Disconnect all your electrical gadgets in the house (including small indicating lamps) and see if the meter is working. If yes, then it means that some leakage of current is taking place in the building (see question 6 for details with regard to effect of leakage current on billing).

Switch of the supply through Switch ‘SW’ Note done the initial reading of energy meter of the switch ON note down the reading of Voltmeter and ammeter. Let the energy meter run for 10 minutes. Again note down the energy meter reading after 10 minutes. A set readings may be obtained after an interval of 5 or 10 minutes and noted in the following note

What is the basic difference between the working of old electromechanical meters and new electronic meters?  Why the utilities have switched over to new electronic meters when both are ISI marked?

Electromechanical Energy Meter (Old Meters)- Most of the residential buildings have got single phase, two wire power supply (one phase and one neutral wire). The typical connections, accordingly are shown below:

* Load i.e. lamps, tube lights, fans, coolers, geysers, refrigerator and other electrical appliances, which consume electrical energy.

Electromechanical Energy Meter - SCHEMATIC Diagram

As shown above, in the conventional energy meter, the measuring element (which senses energy consumed is provided only on phase circuit does not have any such measuring element.

For a non-technical person/common consumer, it can be explained that energy/current enters the meter through phase wire, passes through the measuring element of energy meter, reaches lamps/electrical gadgets, etc. in the house and goes back through neutral wire as can be seen above in the typical diagram.

The conventional energy meter records energy based on the current, which enters the energy meter and is measured by the measuring element installed in the phase circuit.

Keeping above working principle in mind, the electromechanical energy meters were earlier installed by the Electricity Boards/Utilities/Contractors at the residence and wiring of phase and neutral was also accordingly done.

Neutral wires in the house in some of the multi-storey building were joined together by the electrical contractors for economy reasons/easy connections in less time and the meters as such were working fine with that wiring arrangement.

Problems Encountered by Distribution companies in electromechanical meters As no measuring element was used in return circuit i.e. neutral wire in electromechanical meters as indicated in the above diagram tampering was easily possible in such meters e.g. reverse phase running, etc. In a tampered meter, it is possible to run the meter as and when required with simple operation of a toggle switch.

To deal with tampering problems, a need was felt to have a meter, which has measuring element in neutral circuit also as shown below: 

* Load i.e. lamps, tube lights, fans coolers, geysers, refrigerator and other electrical appliances, which consume electrical energy.

Electronic Energy Meter – Schematic Diagram

Electronic Meter - In order to minimize the possibilities of pilferage of energy through tampering of meters, have more accurate recording of energy consumption and have meters, which do not get appreciably affected by mechanical and magnetic disturbances, use of electronic meter was started by electricity boards/utilities. The typical schematic diagram of electronic meter indicated above may be seen.

With above features in place, the electronic meters started recording readings even if some tampering had been done with the meter. Manufacturing have provided indicating lights i.e. LEDs also in some of the electronic meters, which help the utilities to detect tampering or wrong connections done, if any, if inadvertently, the connections have been done wrongly within the meter at the time of manufacturing or at the time of installation e.g. load side connected to supply side etc., then also the LED on the meter will glow indicating that something wrong has taken place. Therefore, we must keep a vigil on these LEDs mounted on the energy meters as wrong connections can also make the meter run fast. If such LEDs keep on glowing, then we must inform the utilities for doing the needful Generally, LED for ‘Power On’ glows when power is ON and LED for ‘CA:’ (i.e. calibration) blinks when meter is recording energy consumption. Other LEDs on the meter, if glow indicate that some wrong connections/ tampering with meter has been done.

      In addition to having measuring element in neutral circuit, electronic meters have one more built-in feature i.e. comparator which compares the current flowing between the phase measuring element and neutral measuring element. This comparator senses both these currents, and considers only the higher value of current for energy metering.

So, in order to enable the utilities to trap the fraudulent consumers and to raise more accurate bills for the energy consumed by its consumers, the following important additional design features have been incorporated in the present electronic meters:

a)      Measurement of current in neutral/return circuit in additional to phase circuit;
b)      Measurement of higher of the tow currents (one measured by measuring element in phase circuit and other in neutral circuit);
c)      Sensitive/more accurate recording of energy consumed and
d)      Not prone to easy tampering

As stated in Answer No. 2 improper neutral connection is also one of the reasons for fast running of meters and hence inflated bills.

When old electromechanical meters were replaced by new electronic meters and were pressed into service, a practical problem in. it is due to the neutral connection wiring which was done earlier keeping in mind the characteristics of electromechanical meters, which did not have measuring element in neutral circuit and did not get affected by neutral wiring/joining. The problem is however more prominent in the case of multi-storey buildings where more than one energy meters are installed on common bus bar (at one place/side-by-side).

Let us try to understand the problem with respect to improper neutral connections through details and illustrations given below: 

1. Please see Illustration 1.

i)                    In case of House No. I₁ current is entering the house and I_{1 -} X₁ current is going out of the house/meter. Since it 1₁ is more than I_{1 x X}I_1, therefore the meter will register energy corresponding to load current I₁ which is okay.

ii)                   In case of House No. 2, I₂ current is enfettering the House and I₂ + (X_{1 –} X₂) current is going back. Since I₂ + (X₁ – X₂) is more than 1₂, therefore, in this case, the neutral measuring element will start sensing an the meter will record energy as per I₂ + (I₂ -I₂) which is higher than the actual energy consumption of House No. 2.).

iii)                 In case of House No. 3 1₃ current is entering the House and I₃ + X₂ is returning back through neutral which is higher than I_3. Therefore, energy corresponding to I₃ + X₂ will be recorded by the electronic meter which is more than the actual energy consumption of House No. 3.

 So in above case only House No. 1 is getting exact bill and House No. 2 & 3 are getting inflated bills.

            Note : For correct connections, break the neutral wire at A, B & C and remove the wire between A – B and B- C points.

2. Please see Illustration 2.
3. Please see Illustration 3.

From above three illustrations, we may note that even if our meters are working satisfactory we may get inflated bills because of improper neutral connections.

Illustration 1:

Illustration 2

Improper Neutral Connection

 *Load i.e. refrigerator, lamps, tube lights, fans, coolers, geysers and other electrical appliances, which consume electrical energy.

 Form above illustration we see that if improper neutral … between House No. 1&2 then following would be the situation.

1. In House No. 2, I₂ current flows in both circuits, electronic meter will record accurately i.e. corresponding to I₂ current, which is the actual consumption.

2. n House No. 1, in the neutral circuit I₁ + I₂ current flows (In is the consumption of House No. 1 and I₂ is the consumption of House No. 2). Therefore, House No. 1 will pay bill for the consumption on House No. 1 & 2 both (corresponding to current I₁ + I₂ in the neutral circuit)

 Note : For correct connections, break the neutral at A and provide neutral connection to each of the house

Illustration 3

Improper Neutral Connection 

·        Load i.e. refrigerator, lamps, tube lights, fans, coolers, geysers and other electrical appliances, which consume electrical energy.

 In above illustration, we see that in House No. 1 no load is connected to supply e.g. the House is locked and no energy consumption is there.

i)                    In House No. 2, energy is being consumed as per current I₂ which is flowing both in phase as well as neutral circuit.

ii)                   In House No. 1, no current is flowing in phase circuit. But because of improper neutral connection, I₂ current is flowing in its neutral circuit (which is basically the current of House No. 2). The electronic meter will sense this I₂ current and register energy accordingly when the House No. 1 is locked and no energy is being consumed by them.

 Note : For correct connections, break the neutral at A and provide separate neutral connection to each of the house

One reason could be the more accurate and sensitive nature of the electronic meters as compared to electromechanical meters. The electromechanical meters, with the passage of time and also by virtue of their design, did not record energy if consumed in very small quantity. They were generally of class 2. But the electronic meters in addition to being sensitive have accuracy of class 1 i.e. they can record energy within an accuracy of + 1% so, now, whatever small energy consumption we have by virtue of indicating lights, LEDs on switch boards, leakage of current due to old house wiring etc., gets recorded by highly sensitive and more accurate electronic meters.

We may also not be aware of the fact that some equipments e.g. TVs, DVDs, etc. when switched off through remote controls continue to consume energy unless they are switched off from the switch mounted on the equipment itself.

Thus we find that there occurs a continuous waste of precious electrical energy (almost 24 hours energy drain). It is true that because of above reason there would be marginal increase in the electricity bill but then why unnecessarily pay for the energy, which in fact has not been utilized by us for fulfillment of our necessities or comfort Let us remember, “Energy Saved is Energy Produced”.

There could be a personal error on the part of meter reader while taking reading, which may also result in excess billing. The errors in the software used by utilities for computing and generating bills electronically may also be one of the reasons that the bills are inflated. For such reasons, distribution companies may be approached with a request to issue revised bills for the actual energy consumed.

It is also true that electromechanical meters, which were installed a few years ago, had started running slow due to moving components in the meter getting worn out. Now since electronic meters have replaced old meters and electronic meters are accurate and sensitive, new meters have started recording the actual energy consumption when electricity bills generated by new electronic meters are compared with old electromechanical meters, there is a feeling that the bills are inflated but it is only psychological. In fact, old meters with the passage of time had started running slow and new meters are registering actual energy consumption. So, this erroneous notion also needs to be dispelled.

As per Gazette Notification No. S.O. 189(E) dated 17 Feb. 2003 – Electrical Wires Cables, Appliances and Protection Devices & Accessories (Quality Control) Order, 2003 issued by the Ministry of Commerce & Industry, energy meters have come under mandatory certification we.f. 17^th August 2003. As per this order, nobody can manufacture, store and sell energy meters without bearing ISI mark. Following three standards have come under compulsory certification scheme of Bureau of Indian Standards (BIS).

 a)   IS 13010:2002             -           Electromechanical Meters

b)   IS 13779:1999             -           Electronic Meter

c)   IS 14697:1999             -           Transformer Operated Meters (for bulk consumers)

All the electricity boards/utilities have to ensure as per above Gazette Notification that all the meters purchased by them and installed at consumer’s end bear ISI mark, which means that these meters conform to the requirements laid down in relevant Indian Standards.

If any electricity board specifies any additional features in their tender, then manufacturer may provide these features in the meters supplied to electricity boards/utilities but in any case these meters should meet the requirements specified in relevant Indian Standards as indicated above. These additional features may be some constructional requirements or anti-tampering features etc

Yes, the Indian Standards on Energy Meters used for domestic purpose have been aligned with the International Electro technical Commission (IEC) standards. The corresponding IEC standards are given below:

Above IEC Standards have been recently restructured at IEC level as follows: 

a)      IEC 62053-11, for electromechanical meters

b)      IEC 62053-21, for electronic meters

c)      IEC 62052-11, for general requirements, tests & test conditions of metering equipments.

The above Indian Standards adequately cover the performance requirements including accuracy under the effect of influence quantities like temperature etc. and their methods of tests which are in accordance with the well established and internationally accepted test methods according to IEC standards.

There are nearly 30 tests given in Indian Standard for electronic meters (IS 13779:1999) which are of relevance to all the stakeholders i.e. manufactures, utilities and consumers. Out of these 30 tests, a few of the tests of common interest are given below:

a)      Test of running on no-load condition – As per this test, it is ensured that if the consumer is consuming no electrical energy, then energy meter should not run. This test is of more relevance to the consumers and is required to be carried out on each meter by the manufacturer.

b)      Test of starting condition: This test has more relevance to the electricity boards/utilities. As per this test, the meter shall be fully functional within 5 seconds after the power supply is switched ON. The meter shall start and continue to register energy consumption at 0.4% of basic current (for a Class 1 meter) of the meter e.g. a 0-10 A meter should start running at 0.04 A i.e. at 40 milliamp ere of current i.e. at about 7-8 W of load. Similarly, a 0-5 ampere meter should start (registering energy even if as small as about 3.5-4 W load is connected to it. Manufacturers are required to carry out this test also on each meter.

c)      Test of accuracy requirements – Manufacturer, at his end, calibrates meters with a duly calibrated standard meter of higher accuracy to ensure that error of each and every meter is within limits specified in Indian Standard (at different values of current and power factor). Most of the electronic meters are of class 1 accuracy as against class 2 accuracy of electromechanical meters. The permissible limits of error of class 1 meter are ± 1% at basic current and unity power factor. This means that recording that recording of energy consumption in electronic meters of class 1 accuracy is very accurate from the consumer as well as electricity boards/utilities point of view. The average consumption of a household varies depending upon their individual consumption pattern. Presuming that energy consumption is 400 units per month and meter is operating at an error of ± 1% the indicated consumption would vary by ± 4 units per month at the most.

It may be noted that records for all tests including the above tests (which are carried out on whole production as per Scheme of Testing & Inspection (STI) prepared by BIS and accepted by manufacturers) are maintained by the manufacturers who have been granted license by BIS under its product certification scheme. BIS verify these records periodically through surprise inspections during which testing in factory, sampling for independent testing, etc., is also done. 

Details indicated above are for reference only. Exact wattage of any appliance may be seen from the rating plate affixed on the appliance. Based on the same and actual number of hours it is run/operated, one can compute the actual energy consumption per day and when it is multiplied by 30/31, we can find out the energy consumption per month by that appliance. Further, based on electricity tariff, we can on our own, cross-examine the monthly electricity bill which indicate the units consumed in kilo-watt hours (kwh) and amount to be paid by us for the electrical energy consumed by us. This cross-verification of units consumed in our house would at least give us an idea that whether our electricity consumption recorded by electricity meters installed by power distribution companies and indicated in electricity bills are comparable and satisfactory or not.

However, we may not forget that apart from the energy consumption in appliances indicated above, there is some energy, which is also consumed by equipments like indicating lamps on switch-boards; transformer operated equipments; batteries under charging; gadgets which are not properly switched off (switched off through remote only) and continuous drain of electrical energy through old house-wiring etc. This energy consumption may also be taken into account while calculating number of units consumed every month.