dimensions, markings and other construction requirements

Schneider Electric Rev 0 2

Regulating Accuracy

The growth of non-linear loads and renewable power generation in modern electrical

distribution networks are the new normal operating conditions for electrical power

meters. The result of these loads – distorted waveforms and various power quality

phenomena – make it necessary to regularly reevaluate and revise the standards and

requirements that continue to guide new power meter designs. This is most notable

in the latest ANSI C12.20-2015 standard, particularly its new accuracy class 0.1 (and

upcoming accuracy class 0.1S, expected to be added in IEC 62053-22 edition 2).

The American National Standards Institute (ANSI) coordinates the development and

use of voluntary consensus standards in the United States and represents the needs

and views of U.S. stakeholders in standardization forums around the globe. The

Institute is the sole U.S. representative and member of the two major non-treaty

international standards organizations, the International Organization for

Standardization (ISO), and, via the U.S. National Committee (USNC), the

International Electrotechnical Commission (IEC)1.

Even though the compliance with ANSI standards is voluntary, most North American

utilities and utility commissions use the ANSI metering standards as reference and

the basis for their revenue (billing) meter testing requirements.

In recent years both ANSI C12.1 and ANSI C12.20 metering standards have been

revised with the intent to bring them up to date with the progress of technology and

the changing regulatory environment.

This white paper discusses the major changes introduced in the latest revisions of

the ANSI C12.1-2014 and ANSI C12.20-2015, and their impact on the new meter

testing, and new meter type approvals. Only requirements applicable to energy

meters are discussed.

The ANSI C12.1-2014 (American National Standard for Electric Meters — Code for

Electricity Metering) covers all types of electricity revenue meters and other

instruments such as demand meters, pulse devices, and auxiliary devices. This

standard specifies the requirements common to all ANSI meters, such as reference

conditions, design acceptance test procedures, insulation tests, electromagnetic

compatibility tests, environmental tests and mechanical tests. In particular, the

performance requirements for active a.c. energy meters of accuracy classes 1 and

0.5 are also specified.

The ANSI C12.20-2015 (American National Standard for Electric Meters for

Electricity Meters – 0.1, 0.2 and 0.5 Accuracy Classes) references a number of

common meter requirements, test and test conditions from ANSI C12.1, and

contains particular performance requirements for active a.c. energy meters of

accuracy classes 0.1, 0.2 and 0.5. It applies only to Blondel Theorem compliant

meters, i.e. meters implementing N-1 watt-meter elements for N wires of the

measured poly-phase electrical system. Where differences exist between ANSI

C12.1 and ANSI C12.20, the more demanding requirements of higher accuracy

classes in ANSI C12.20 prevail over the specifications of ANSI C12.1.

Both ANSI C12.1 and ANSI C12.20 reference common meter construction

requirements given in ANSI C12.10 2015 (American National Standard for Electric

Meters for Physical Aspects of Watthour Meters – Safety Standard). This standard

specifies the electrical connections of the meter service terminals, pertinent

1 «Introduction.» American National Standards Institute - ANSI. American National Standards Institute.

Web. 12 Apr 2018. https://www.ansi.org/about_ansi/introduction/introduction?menuid=1


Regulating Accuracy

dimensions, markings and other construction requirements for both socket and

bottom connected meters.

While the ANSI meter standards contain some safety tests and requirements, such

as insulation tests, the general product safety and electrical safety requirements for

socket (type S, or S-base) and bottom-connected (type A, or A-base) meters are

covered in UL 2735 (Standard for Safety for Electric Utility Meters) and its Canadian

equivalent, UL 2735C, which, at this paper’s publication date, is under development.

Both ANSI and IEC metering standards have been used for many decades: the first

American electricity metering standard was published in 1910, while the IEC

Technical Committee 13 (TC13) is one of the first technical committees established

by IEC in the 1920s. Today the TC13 has 33 participating countries and 16 observer

countries, representing expertise of utilities, equipment manufacturers, test

laboratories, and legal metrology organizations.

The evolution of IEC and ANSI series of metering standards has been supported by

participation from experts within equipment manufacturers, regulators, testing

laboratories and electrical utilities.

The most obvious difference between a typical ANSI meter and a typical IEC meter

is form factor: ANSI meters (Figure 1) are round and designed to fit into a

standardized installation sockets, whereas IEC meters (Figure 2) are rectangular

and designed according to the DIN specifications for wall-mounting or DIN-rail

mounting, with terminal blocks for stripped wires.

ANSI and IEC series of standards share many analogous tests and requirements -

they both specify performance tests such as starting current, creep, and accuracy

over a range of load currents, voltages, and power factors. Both series of standards

also specify immunity to external influences such as electromagnetic phenomena,

environmental conditions and mechanical stresses. However, many of the less

obvious differences may be identified in the performance specifications, test

conditions, construction requirements, and testing methodology.


Regulating Accuracy

ANSI standards define values of maximum meter current: 2A, 10A, 20A, 200A, 320A

– values which are the designations of the meter current classes. All the other load-

based performance requirements are based upon that classification. The accuracy

of ANSI meters is evaluated with respect to ‘reference conditions’. A ‘reference

condition’ is a load current test point that may be the current value known as ‘test

amps’ (TA), or a different reference current value specified for an individual test. The

values of the reference current test points may vary depending on the meter current

class. Meter accuracy at each reference test point must be “as close as practical to

zero error”2 3, with limits set out for each accuracy class.

The IEC standards do not use a current class designation, but instead define the

meter nominal (or rated) current value In for transformer operated meters, and the

base current Ib for directly connected meters. These load current operating points

are used as reference values for other load-based performance tests. For IEC

meters the maximum current Imax is specified as “preferably an integral multiple”4 of

In (or Ib), with a minimum permissible value of 1.2 In (or Ib). The preferred values for

In are: 1, 2, 5 A. The preferred values for Ib are: 5, 10, 15, 20, 30, 40, 50, 63, 80,

100, 125 A.

The accuracy of IEC meters is evaluated with respect to a reading of a reference

meter, with a permissible displacement of the zero-error line defined for each

accuracy class, as means of correcting errors of measurement resulting from

uncertainty of equipment calibration and other parameters capable of influencing the

measurement results;

An approximate, high-level correspondence between ANSI and IEC series of

metering standards are presented in Table 1:

2 ANSI C12.20-2015 American National Standard for Electricity Meters— 0.1, 0.2 and 0.5 Accuracy

Classes

3 ANSI C12.20-2010 American National Standard for Electricity Meters— 0.2 and 0.5 Accuracy Classes

4 ANSI C12.20-2015 American National Standard for Electricity Meters— 0.1, 0.2 and 0.5 Accuracy Classes


Regulating Accuracy

Notes:

A more detailed comparison of these standards in beyond the scope of this paper.

“Most of the specifications in ANSI C12.1-2014 have been retained from the

previous edition. Changes to the temperature rise test were made to make testing

consistent with the tests in the meter socket standard, ANSI C12.7. The ANSI

C12.1-2014 section 5, Standards for new and in-service performance, and Appendix

D were extensively updated to reflect current practices. For several of the tests,

specific details for successful tolerance criteria have been modified, and test

requirements for bidirectional metering have been added. Some definitions were

also added and references to external documents were updated.”5

The existing ANSI C12.20 standard – published in 2010 – was broadened by the

ANSI C12.20 -2015 edition “to allow three phase current and voltage sources as an

optional test method to the existing single phase, series, parallel method. Other

major changes include testing under harmonic conditions, addition of a 0.1%

accuracy class, clarification that non-Blondel applications are not covered by this

standard, and addition of specifications for the optical port pulse outputs. ”6

Both ANSI C12.1-2014 and ANSI C12.20-2015 specify accuracy classes 0.5. The

differences between these two specifications may not be obvious, but they are

important for the user since they may result in significant differences in meter

performance under some operating conditions.

In the most general sense, the ANSI C12.1-2014 class 0.5 may be applied to meters

which do not adhere to the Blondel theorem. On the other hand, the ANSI C12.20

class 0.5 specification applies only to meters which meet the Blondel’s theorem.

5 ANSI C12.1-2014 American National Standard for Electric Meters, Code for Electricity Metering.



Regulating Accuracy

ANSI C12.20-2015 explains that “non-Blondel metering installations assume

balanced line voltage magnitudes and phase angles. Unbalanced line voltages will

introduce measurement registration error independent of instrumentation accuracy. ”7

Typical Blondel and non-Blondel meter form designations are listed in ANSI C12.20-

2015 clause 4.4.

In addition, a meter of ANSI C12.20-2015 accuracy class 0.5 will have to pass the

tests of harmonic influences, whereas such influence tests are not required in ANSI

C12.1-2014.

Meter accuracy classes are defined in IEC standards and in ANSI standards, and

marked by an accuracy class index, which is a number representing the maximum

meter percent error at reference test conditions. Other metering standards such as

CENELEC EN 50470-x or OIML R46 recommendations also define meter accuracy

classes, but use capital letters as accuracy class indices. For example, the

“accuracy class C” defined in EN 50470-3-1 standard or OIML R46 recommendation

roughly corresponds to “accuracy class 0.5” defined in the IEC 62053-22 standard,

or in the ANSI C12.20 standard. A detailed analysis of differences between these

accuracy classes is outside of the scope of this paper.

The ANSI C12.20-2010 specified accuracy classes 0.5 and 0.2. A notable

development in the ANSI C12.20-2015 standard is the introduction of a new

accuracy class 0.1. Using an example of three-element current class 20 meter,

Figures 3 and 4 summarize the performance differences between accuracy classes

specified in the ANSI C12.20-2015.


Classes.


Regulating Accuracy

Permissible errors at each test point given in ANSI C12.20 are specified with respect

to the reference condition - the error at this reference condition is measured when

the meter is stabilized at room ambient temperature, rated voltage, rated frequency,

“test amperes” (TA) current, unity power factor, and sinusoidal waveforms (ANSI

C12.20-2015 section 5.5.1 specified tolerances for all these reference test

conditions). “The meter performance under the test conditions [..] shall be as close

as practical to zero error and in no case shall exceed 0.2% error for accuracy class

0.5, 0.1% error for accuracy class 0.2, or 0.05% error for accuracy class 0.1.”8 9

For a discussion of the benefits of high accuracy metering, please refer to the

Schneider Electric white paper “A high accuracy standard for electricity meters” by

Lance A. Irwin (2011).

Previous editions of ANSI C12.1 and NASI C12.20 did not clearly state a

requirement for testing of bidirectional meters with energy flowing in the “delivered”

and “received” directions.

The latest edition of ANSI C12.1-2014 clarifies that if the meter is designed for

measurement of energy in both directions, then the test conditions shall be applied

twice, once with energy flowing only in the forward or “delivered” direction, and once

with energy flowing only in the reverse or “received” direction.10

The requirement for testing in both directions applies to the starting load tests, the

load performance tests and the test of variation of power factor.

The same clarification is not included in the ANSI C12.20, but presumably it also

applies.

8 ANSI C12.1-2014 American National Standard for Electric Meters, Code for Electricity Metering


10 ANSI C12.1-2014 American National Standard for Electric Meters, Code for Electricity Metering.

http://www2.schneider-electric.com/documents/support/white-papers/998-4531_electric-utilities_High-accuracy_EN.pdf


Regulating Accuracy

Due to the proliferation of non-linear loads and renewable power generation in

modern electrical distribution networks, distorted waveforms and various power

quality phenomena are a common occurrence and should be considered as normal

operating conditions for electricity meters. The industry experience and numerous

academic studies demonstrate that some static electricity meters cannot correctly

measure electrical energy in distorted waveforms. Modern static electricity meters

seem to be more sensitive to distorted waveforms than the induction (Ferraris)

electromechanical meters. The sensitivity of static meter to the waveform distortions

depends on many factors, including the implemented measurement algorithms,

signal conditioning and filtering, or even the type of current or voltage sensors11 12 13

[6, 7, 9]. Many publications reported accuracy-related problems with meters exposed

to highly distorted waveforms14 15 16 17, albeit without precisely identifying the root

causes.

Metering errors induced by highly distorted waveforms may have significant impact

in revenue billing applications, but their causes and nature are not well understood;

consequently, comprehensive tests for influence of distorted waveforms are often

not included in meter type approval programs.

Some basic tests with distorted waveforms are prescribed in the IEC metering

standards and in the OIML R46 recommendations, however the ANSI C12.20-2015

specifies probably the most comprehensive harmonic influence testing to date.

The ANSI C12.20 introduces six tests of meter accuracy under the influence of

distorted waveforms (tests #39 – #44).” The purpose of these tests is to verify that

the meter maintains accuracy under a variety of non-sinusoidal voltage and current

conditions.”18

11 F. Leferink, C. Keyer, and A. Melentjev, .Static energy meter errors caused by conducted

electromagnetic interference,. IEEE Electromagnetic Compatibility Magazine, vol. 5, no. 4. pp. 49.55, 2016.

12 A. Ferrero, M. Faifer, and S. Salicone, .On Testing the Electronic Revenue Energy Meters,. IEEE Transactions on Instrumentation and Measurement, vol. 58, no. 9. pp. 3042.3049, 2009.

13 Quijano Cetina, R. and Roscoe, Andrew J. and Wright, P.S. (2017) A review of electrical metering accuracy standards in the context of dynamic power quality conditions of the grid. In: 52nd International Universities Power Engineering Conference (UPEC), 2017. IEEE, Piscataway, N.J.. ISBN 978-1-5386-2345-9 , http://dx.doi.org/10.1109/UPEC.2017.8231871

14 F. Leferink, C. Keyer, and A. Melentjev, .Static energy meter errors caused by conducted electromagnetic interference,. IEEE Electromagnetic Compatibility Magazine, vol. 5, no. 4. pp. 49.55, 2016.

15 A. Ferrero, M. Faifer, and S. Salicone, .On Testing the Electronic Revenue Energy Meters,. IEEE Transactions on Instrumentation and Measurement, vol. 58, no. 9. pp. 3042.3049, 2009.

16 A. Domijan Jr., E.Embriz-Santander, A. Gilani, Watthour meter accuracy under controlled unbalanced harmonic voltage and current conditions, IEEE Transactions on Power Delivery, Vol. 11, No. 1, Jan 1996.

17 Quijano Cetina, R. and Roscoe, Andrew J. and Wright, P.S. (2017) A review of electrical metering accuracy standards in the context of dynamic power quality conditions of the grid. In: 52nd International Universities Power Engineering Conference (UPEC), 2017. IEEE, Piscataway, N.J.. ISBN 978-1-5386-2345-9 , http://dx.doi.org/10.1109/UPEC.2017.8231871



Regulating Accuracy

Table 2 below shows the adoption of the harmonic influence test in various metering

standards. The only tests listed are those representing long-term or continuous

waveform distortions capable of influencing the accuracy of energy measurements.

For each of these influence conditions the metering standards specify some level of

allowable degradation of measurement accuracy.

● ● ● ●

●

● ●

●

● ●

●

●

●

https://www.nema.org/Standards/Pages/American-National-Standard-for-Electricity-Meters-0-2-and-0-5-Accuracy-Classes.aspx?_sm_au_=iNVSnzF7ZVQ7LPLH


http://www.iec.ch/?_sm_au_=iNVSnzF7ZVQ7LPLH



Regulating Accuracy

●

● ● ●

● ● ●

U5 = 10 % of Un (IEC, EN)

U5 = 5 % of Un (OIML)

I5 = 40 % of I fundamental

● ● ●

Superimposed current

harmonics sweep:

2 -150 kHz

○ ●3)

Superimposed harmonics

sweep: 15 fn - 40 fn

Superimposed harmonics

sweep: 15 fn - 40 fn

●

Notes:

Table 2 does not list short-term, transient phenomena (disturbances) since the

metering standards do not specify any allowable accuracy degradation for such

conditions.

Both the influences and disturbances are also considered as a part of meter

electromagnetic compatibility testing.






Regulating Accuracy

The test output facilitates the most commonly used meter accuracy test methods

which are based on counting the energy test impulses. All metering standards, ANSI

and IEC alike, specify that a meter shall be equipped with a test output proportional

to the measured energy and compatible with external devices typically used to

check the registration of the meter both during type approval testing and during

verification testing in field installations. The optical test output is the preferred

implementation of a test output and the latest edition of ANSI C12.20-2015 provides

clarified requirements for its acceptable implementations.

As per ANSI C12.20-2015, the optical test output may be implemented as ANSI

Type 2 optical port according to the ANSI C12.18, with its function switched between

normal communications and the energy pulsing (called “optical port Type A”), or as

a separate port constructed according to the characteristics given in the Annex C of

the ANSI C12.20-2015 (called “optical port Type B”). In either case, the test output

must be accessible in normal use, without removing the meter cover.

Meters that measure delivered and received energy, or can measure other time

integrated quantities, such as VARh, VAh, V2h etc., are expected be able to use the

test pulse output for these measured quantities. In such meters, a single physical

test output may be used for these measured quantities only when a method is

available to select which quantity is being output on the test port, and when a visible

indication is present as to which quantity is currently active.19


Classes


Regulating Accuracy

While the largest markets for ANSI standard electricity meters are in the United

States, Canada and Mexico, ANSI C12 electricity metering standards are also used

in many countries around the world, especially by utilities in parts of Asia, Central

America and South America. In many cases, notwithstanding the non-ANSI form

factors, the accuracy specifications of ANSI standards are applied to evaluate or

describe performance of industrial panel meters, power monitors (PMDs), branch

circuit power meters (BCPMs) or even power quality instruments (PQIs).

The latest revisions of C12.1 and C12.20 introduce many new requirements, and

provide several important clarifications which influence new meter designs and type

testing. At the cost of modest increase in the number of tests and consequently a

higher cost of meter type approvals, these new revisions provide the benefits of

higher accuracy class 0.1 metering, increased meter robustness, and increased

metrological performance with highly distorted signals. These new requirements

make ANSI revenue meters more suitable for use on modern electricity distribution

networks and result in meter designs updated to match the technical progress in

metrology, and the increased customer expectations of more robust and more

accurate measurements in billing applications.

Piotr Przydatek

Sandra Pedro


Regulating Accuracy

«Introduction.» American National Standards Institute - ANSI. American National Standards

Institute. Web. 12 Apr 2018.

https://www.ansi.org/about_ansi/introduction/introduction?menuid=1

ANSI C12.1-2014 American National Standard for Electric Meters, Code for Electricity

Metering

ANSI C12.1-2008 American National Standard for Electric Meters, Code for Electricity

Metering

ANSI C12.20-2015 American National Standard for Electricity Meters— 0.1, 0.2 and 0.5

Accuracy Classes

ANSI C12.20-2010 American National Standard for Electricity Meters— 0.2 and 0.5 Accuracy

Classes

IEC62052-11 Electricity metering equipment (AC) – General requirements, tests and test

conditions – Part 11: Metering equipment, First edition, 2003.

F. Leferink, C. Keyer, and A. Melentjev, .Static energy meter errors caused by conducted

electromagnetic interference,. IEEE Electromagnetic Compatibility Magazine, vol. 5, no. 4.

pp. 49.55, 2016.

A. Ferrero, M. Faifer, and S. Salicone, .On Testing the Electronic Revenue Energy Meters,.

IEEE Transactions on Instrumentation and Measurement, vol. 58, no. 9. pp. 3042.3049,

2009.

A. Domijan Jr., E.Embriz-Santander, A. Gilani, Watthour meter accuracy under controlled

unbalanced harmonic voltage and current conditions, IEEE Transactions on Power Delivery,

Vol. 11, No. 1, Jan 1996.

Quijano Cetina, R. and Roscoe, Andrew J. and Wright, P.S. (2017) A review of electrical

metering accuracy standards in the context of dynamic power quality conditions of the grid.

In: 52nd International Universities Power Engineering Conference (UPEC), 2017. IEEE,

Piscataway, N.J.. ISBN 978-1-5386-2345-9 , http://dx.doi.org/10.1109/UPEC.2017.8231871

Daniele Gallo, Carmine Landi, Nicola Pasquino, Nello Polese, A New Methodological

Approach to Quality Assurance of Energy Meters Under Nonsinusoidal Conditions, IEEE

TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 56, NO. 5,

OCTOBER 2007

Lance A. Irwin, “A high accuracy standard for electricity meters” , April 2011,

http://www2.schneider-electric.com/documents/support/white-papers/998-4531_electric-

utilities_High-accuracy_EN.pdf

EPRI, .Accuracy of Digital Electricity Meters.. Electric Power Research Institute, Palo Alto,

California, USA, 2010.

P. S. Filipski and P.W. Labaj, Evaluation of reactive power meters in the presence of high

harmonic distortion, IEEE Trabsactions on Power Delivery, Vol. 7, No. 4, Oct 1992.

P. S. Filipski and R. Arseneau, .The Effects of Nonsinusoidal Waveforms on the Performance

of Revenue Meters,. National Research Council Canada,1990

https://www.ansi.org/about_ansi/introduction/introduction?menuid=1

http://dx.doi.org/10.1109/UPEC.2017.8231871



dimensions, markings and other construction requirements

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