S-S-06—Sampling plans for the inspection of isolated lots of meters in service

Category: Statistical methods
Issue date: 2023-02-17
Effective date: 2023-02-17
Revision number: 3
Supersedes: S-S-06 (rev. 2)

Table of Contents

1.0 Scope

This specification establishes the requirements that are applicable to isolated lots of homogeneous in-service electricity or gas meters, where a meter owner has chosen to use sampling inspection for the purposes of extending the reverification period of a lot of meters in service.

Note:

  1. Where applicable, this specification may be used as an alternative to performing 100% meter reverification, upon expiry of a meter lot's initial or subsequent reverification period.
  2. Sampling plans, by design, contain inherent risks and limitations with regard to their usage and the conclusions they may or may not provide. Meter owners are therefore advised that, although conformity with the requirements of this specification may allow for the extension of a meter's reverification period, relying solely on the use of the sampling plans contained in this specification will not provide users with an assurance of compliance with the metering accuracy obligations prescribed under the Electricity and Gas Inspection Act.

2.0 Authority

This specification is issued under the authority of section 19 of the Electricity and Gas Inspection Regulations.

3.0 References

4.0 Administrative requirements

Sampling inspection must be carried out well in advance of the expiry of the reverification period of the meters so that in the case of nonconformity with the requirements, all meters forming part of the lot can be removed from service prior to the expiry of the reverification period.

5.0 Sampling inspection requirements

5.1 Lot formation

The following requirements apply:

  1. The lot must be formed from meters that are homogeneous with respect to the requirements in Annex A.
  2. At the discretion of a meter owner, larger lots may be reformed into multiple lots of smaller size.

5.2 Sample selection

The following requirements apply:

  1. The sample must be drawn at random without replacement from the lot listing using authorized random sampling software that meets the requirements referenced in S-S-01.

    Note: Systematic sampling is not allowed.

  2. The size of the sample must be one obtained from the applicable table in Annex C as per the sampling instructions provided by this specification. The sample representing the lot must correspond to a value between the minimum sample size (nmin) and maximum sample size (nmax) as identified in the table of Annex B.
  3. Each meter included in the sample must satisfy the following conditions:
    1. be currently installed in service;
    2. not have had its metrological parameters adjusted post installation, unless otherwise specified in the relevant Measurement Canada (MC) specification for the verification and reverification of the subject meter type or class;
    3. meet the homogeneity criteria stated in section A.1 of Annex A; and
    4. meet the total time on test criteria stated in section A.2 of Annex A.
  4. Where a sample meter does not meet the conditions stated in 5.2(c), the following requirements apply:
    1. The meter must not be considered as part of the sample group for performance testing purposes and must be replaced by the sequentially subsequent meter on the preselected unsorted sample meter listing that meets the applicable criteria.
    2. The exclusion rationale for the subject meter(s) must be reported as per 5.3(d).
  5. Where a meter, which has been removed from service, is not capable of having its performance assessed in accordance with the requirements of this document, the following requirements apply:
    1. The meter must not be considered as part of the sample group for performance testing purposes and must be replaced by the sequentially subsequent meter on the preselected unsorted sample meter listing that meets the applicable criteria.
    2. The exclusion rationale for the subject meter(s) must be reported as per 5.3(d).
  6. When a meter is not accessible and therefore cannot be removed from service to assess its performance in accordance with the requirements of this document, the following requirements apply:
    1. The meter must not be considered as part of the sample group for performance testing purposes and must be replaced by the sequentially subsequent meter on the preselected unsorted sample meter listing that meets the applicable criteria.
    2. The exclusion rationale for the subject meter(s) must be reported as per 5.3(d).
  7. Meters which have been excluded as sample meters as a result of not satisfying the requirements of either 5.2(c) or 5.2(e) must not be returned to the parent lot.
  8. Lots failing to meet the nmin as a result of the total number of exclusions under 5.2(c), are not considered to be homogeneous and do not qualify for a seal extension.
  9. Where a lot is not deemed to be homogeneous, meter owners must implement one of the following actions:
    1. Reform the lot on the basis of both the lot and sample homogeneity criteria specified in Annex A.
    2. Assign a shorter initial reverification period to the lot as per subsection 5.7.
    3. Remove the lot from service.

5.3 Meter sampling records

The following requirements apply:

  1. For each lot assessed, a meter owner must maintain records documenting the following:
    1. a unique, owner-assigned lot number or record reference which includes an ordinal number (e.g. 1st, 2nd, 3rd) indicating the order of occurrence of the lot's assessment under this specification (including the current assessment);
    2. the homogeneity criteria details specified in section A.1 of Annex A;
    3. the utility number and manufacturer's serial number for each meter.
  2. All meters identified by the owner as forming part of the lot must be listed in ascending order based on meter identification numbers or an inventory number generated by the associated informatics system.
  3. The identification of each unsorted sample meter (n to nmax) selected from the lot, the sample meters tested, the quality characteristics examined and the test results obtained must be documented.

  4. All sample meters selected but not included in the final calculations must be accounted for by the meter owner and the reasons for their exclusion must be documented and, on request, made available for MC review.

    Note: Evidence of deliberate exclusion or improper accounting may disqualify the results of the sample's analysis.

5.4 Meter inspection, quality characteristics and corrective actions

The following requirements apply:

  1. Each sample meter must be examined for conformance to all pertinent requirements as prescribed in the relevant MC specification for the verification and reverification of the meter under test.
  2. Sample meters must be inspected under identical conditions and within as short a time period as is practicable to achieve valid inspection results.
  3. In the case of a defective meter, the following requirements apply:
    1. Each defective meter excluded from the final calculations must be :
      • preserved for MC review; and
      • the subject of an investigation by the meter owner to determine the cause of the defect or defects.
    2. A report must be prepared that includes the following information associated with the investigation:
      • details of the meter's make, model, Notice of Approval number, seal year, and identification numbers;
      • a description of the defect and its effect on the meter's operation, including performance test results where feasible;
      • a description of the steps taken to investigate the cause of the defect, including identification of the personnel both performing the investigation and providing information for its purpose;
      • an explanation of how the defect occurred, including where it occurred in the process;
      • an evaluation of the extent of the defect in the immediate situation as well as in situations likely to be similarly affected; and
      • details of the corrective and preventive action proposed or performed to address the cause and symptoms of the defect.
    3. The report must be provided to the local MC representative for review prior to deciding upon the acceptability of the affected lot.
    4. Decisions regarding acceptability of the affected lot and the possible need for further investigation or corrective action must not be made until MC has evaluated the report and the statistical analysis of the data from the sample meters involved in the final calculations.

5.5 Acceptance criteria

5.5.1 Individual meters

The following requirements apply:

  1. Each meter in the sample can be considered acceptable if all of the following conditions are met:
    1. it complies with all specified reverification performance requirements prescribed in the relevant MC specification for the verification and reverification of the meter under test;
    2. it does not possess any defect which could affect its ability to meet specified requirements during its usage; and

    3. it has been obtained from a population whose seal year is still valid.

      Note: Where a meter in the sample is received with a broken seal, the meter is considered acceptable only if an exclusion as per 5.3(d) cannot be justified.

  2. To maintain overall homogeneity of the lot, sample meters, obtained from lots qualifying for an extension of the reverification period, which meet reverification requirements and have been granted the same extension as the parent lot, should, wherever possible, be returned to the parent lot and reinstalled following acceptance of the lot.

    Note:Alternatively, these meters can be reverified.

  3. Where sample meters require their seals to be broken in order to conduct meter performance testing, precautions should be taken to ensure the integrity of the results. If the lot is acceptable, the individual sample meters that are also acceptable must be resealed with an additional identifier indicating the original seal year in the sealing assembly. Alternatively, these meters must be reverified.
  4. Sample meters that meet reverification requirements, but have been obtained from lots not qualifying for a an extension of the reverification period, as well as sample meters not returned to the parent lot, must be governed by bulletin E-26 or G-18, with respect to the assigned reverification period.

5.5.2 Meter lots

The following requirements apply:

  1. The sampling plan parameters of ISO 2859-2 as modified in Annex C of this document must be used for the inspection of isolated lots of meters in service.
  2. The acceptability of the lot for the purposes of extending its reverification period must be established on the basis of the performance results of the sample with respect to the demonstrated number of the following meters, as defined in 5.5.3:
    1. type 1 (C1) marginally conforming meters; and
    2. type 2 (C2) nonconforming meters.
  3. Contractors are responsible for ensuring the performance quality of a lot of in-service meters they own. Where a seal extension is available under this specification, contractors must give consideration to their statutory obligation for keeping meters in good repair, when selecting the extension to be applied from those which are available. Specifically, the conformance quality of a lot of meters in service must, in all cases, meet or exceed the declared limiting quality (LQ) that is associated with level 5 (see Annex C).

5.5.3 Meter performance test limits

The following requirements apply:

  1. A meter must be designated as a type 1 (C1) marginally conforming meter or a type 2 (C2) nonconforming meter based on its performance error at any required test point of all performance tests, as follows:

    Table 1—Meter designation and meter performance test limits
    Designation Description Meter performance error
    Type 1 (C1) Marginally conforming meter Exceeds ± 2.0%, unless otherwise prescribed in the relevant MC specification for the verification and reverification of the subject meter type or class
    Type 2 (C2) Nonconforming meter Exceeds ± 2.9%, unless otherwise prescribed in the relevant MC specification for the verification and reverification of the subject meter type or class
  2. A type 2 (C2) nonconforming meter is also counted as a type 1 (C1) marginally conforming meter.

5.5.4 Seal extension levels

The following requirements apply:

  1. The maximum seal extension level available for application to a lot must be established on the basis of satisfying the following criteria when applied to nmin as specified in the columns of the applicable table in Annex C:
    1. Number of type 1 (C1) meters ≤ Actype 1
    2. Number of type 2 (C2) meters ≤ Actype 2
  2. Subject to subsection 5.6, the maximum seal extension level that may be available for application to a lot, is the level associated with the LQ column of the applicable table in Annex C which satisfies the requirements of 5.5.4(a) for the established nmin sample size.
  3. Where the maximum seal extension level available for application to a lot is determined to be level 4, the applicable seal extension, as determined under Annex E, may be repeated without limitation on an ongoing basis where the following criteria are met:
    1. the applicable level 4 LQ criteria of the applicable table in Annex C; and
    2. the time on test criteria of Annex E.
  4. Subject to 5.5.4(e), lots failing to meet at least level 4 criteria are not acceptable for seal extension and all meters in these lots must be removed from service.
  5. Where a lot failing to meet level 4 criteria is capable of meeting the LQ criteria of level 5 (where available), the applicable level 4 seal extension available as per Annex E, may be granted to the lot. However, upon expiry of this extension, the lot cannot be resampled and all meters in the lot must be removed from service.

  6. When a lot fails to meet at least level 4 criteria because the requirement of 5.5.4(a)(ii) is not met, all sample meters identified as type 2 (C2) meters must be held in storage until MC authorizes their further processing.

    Note: The sample meters are required to be held in storage (without just cause) after December 31 of the calendar year in which the sampling was conducted.

5.6 Use of sampling plans (Annex C)

The following requirements apply:

  1. The value of nmin must be:
    1. established on the basis of the lot size and the maximum seal extension level being targeted;
    2. used for establishing the maximum seal extension level, where further movement within the table is limited to either the horizontal or a diagonal downward direction for the same nmin.
  2. Notwithstanding the seal extension level available under 5.5.4(a) and subject to 5.6(c), the maximum seal extension level that may be applied to the lot must be established on the basis of the order of the lot's sampling occurrence under this specification, as specified in annex D.

  3. Where the maximum seal period extension level available for application to the lot under Annex D is greater than the previous seal extension granted to the lot, the extension level applied to the lot must not be more than one level higher than the previous extension.

    Note: The eligibility for the application of a longer period is limited to a single occurrence within a meter lot's in-service life.

  4. Where a lot population:
    1. has never been assessed against the requirements of this specification, the seal extension period of reference for the purposes of 5.6(c) must be the last seal period extension granted to the lot under the previously authorized compliance sampling program;
    2. is re-formed under 5.1(b) or 5.2(i)(i), the maximum seal extension levels available for application to the re-formed lot must be established in accordance with the requirements of 5.6(b), 5.6 (c) and 5.6 (d), as applicable to the parent lot before it is re‑formed.
  5. Where a lot's population size is 500 meters or less, a meter owner may, at their discretion, use the sampling plan as specified in Table C.2 of Annex C. In such a case, the seal period extensions available under Annex E must be reduced by 50% (rounded down to the nearest whole year).
  6. Where a lot's population size is 60 meters or less, a meter owner may, at their discretion, use the sampling plan as specified in Table C.3 of Annex C. In such a case, the only seal period extensions available under Annex E must be those associated with a level 4 extension.

5.7 Seal period extension (Annex E)

Note: For requirements (b) and (d), where months are established on the basis of day counts, one month is to be considered 31 days. Alternatively, months may be established on the basis of actual month days where this information is tracked on an ongoing basis relative to true months completed within a calendar period.

The following requirements apply:

  1. For the types of meter lots indicated below, the time on test requirements which need to be met or surpassed by each sample meter (as per the homogeneity requirements of section A.2 of Annex A) must be established on the basis of the meter's initial reverification period and the minimum seal extension (in months) specified in the "1st extension" column of Table E.1 of Annex E:
    1. new meters still within their initial reverification period;
    2. renewed meters still within their subsequent reverification period;
    3. reserviced meters still within their subsequent reverification period.
  2. For the types of meter lots listed in 5.7(a), a sample meter's time on test (in months) is established from the date the sample meter is placed into service, to the date that it is removed from service (rounded down to the nearest whole month).
  3. Subject to 5.7(e), where a meter lot is still within a previously granted seal period extension, the time on test requirements that need to be met or surpassed by each meter in the sample (as per the homogeneity requirements of section A.2 of Annex A) must be established on the basis of the previous seal extension granted to the lot and the applicable subsequent extension percentage prescribed for the subject row in Table E.1 of Annex E.

  4. For meter lots still within a previously granted seal period extension, a sample meter's time on test (in months) is established from the date that the certificate was issued relative to the meter lot's last seal extension, to the date that the sample meter is removed from service (rounded up to the nearest whole month).

    Note: Alternatively, a sample meter's required time on test is satisfied where it can be demonstrated that it has continuous uninterrupted service.

  5. Meter lots that are sampled on an annual basis under this plan are not subject to the time on test requirements specified in Table E.1 of Annex E.
  6. Where the time on test requirements for the first extension or subsequent extensions of a lot have not been met or where a sample is deemed to not be homogeneous relative to the applicable time on test requirement, a lower initial reverification period (where the time on test requirements are satisfied) may be assigned to the lot.
  7. Once an shorter initial reverification period from a lower row in Table E.1 has been assigned to a lot, further movement within the table is limited to either the horizontal, downward or diagonal downward directions (i.e. the initial reverification period reference cannot be increased on subsequent samplings of the lot).

5.8 Reverification date calculations

The following requirements apply:

  1. Subject to 5.8(b), where a seal period extension is granted under Annex E, the meters in the lot, less any nonconforming meters, must be considered due for reverification on or before December 31 of the calendar year calculated as the sum of the year in which the first sample meter was removed from service and the seal extension (in years) granted under Annex E.
  2. Where the first sample meter is removed from service in the calendar year which immediately precedes the meter lot's seal expiration year, the meters in the lot, less any nonconforming meters, must be considered due for reverification on or before December 31 of the calendar year calculated as the sum of the lot's seal expiration year and the seal extension (in years) granted under Annex E.
  3. Subject to 5.8(d), where a lot of meters fail to meet the requirements for an extension of its reverification period, the meters in the lot must be considered due for reverification on the date established by the previous verification or reverification, as the case may be.
  4. In the case of a lot of meters which fails to meet the requirements for an extension of its reverification period and the first sample meter was removed from service in a calendar year which preceded the meter lot's seal expiration year by more than one (1) calendar year, the meters in the lot must be considered due for 100% reverification, on or before December 31st of the calendar year which postdates the year in which the first sample meter was removed from service.

6.0 Revisions

The purpose of revision 3 was to:

  • clarify the requirements for the time on test of meters within their subsequent reverification period and update Table E.1 of Annex E;
  • clarify the performance test limits for type 1 (C1) and type 2 (C2) meters, some of which are defined in the relevant MC specification for the verification and reverification of the subject meter type or class;
  • update the document according to new formatting requirements.

The purpose of revision 2 was include the clause from section A.1.1 to the homogeneity characteristic of meters with multiple voltages or auto-ranging voltages.

The purpose of revision 1 was to clarify the requirements for the homogeneity of meters with multiple voltages or auto-ranging voltages.

Annex A (normative)—Requirements for lot and sample homogeneity

A.1 Lot homogeneity requirements

Where applicable, the meters in the lot must be homogeneous with respect to the following characteristics as well as those that may be prescribed in the relevant MC specification for the verification and reverification of the subject meter type or class:

Electricity meters

Note: There is an exception for 1-element and 1.5-element meters, as these may be mixed to form a lot.

  • type (transformer or self-contained);
  • manufacturer and model, unless otherwise authorized in accordance with section A.1.1;
  • voltage or voltage range (meters of a given approved voltage that are marked with a subset of nominal voltages or voltage ranges are not to be considered homogeneous with respect to meters marked with a different nominal voltage or voltage range), unless otherwise authorized in accordance with section A.1.1;
  • maximum current range, unless otherwise authorized in accordance with section A.1.1;
  • measurement functions (e.g. measured quantities, energy, demand), unless otherwise authorized in accordance with section A.1.1;
  • firmware version, unless otherwise authorized in accordance with section A.1.1;
  • frequency rating;
  • same model or type of telemetering device (if so equipped), unless otherwise authorized in accordance with section A.1.1;
  • configuration/form (i.e. number of elements, wye, delta or auto configuration);
  • status at time of last inspection (i.e. new, renewed, or reserviced);
  • seal year (same seal year or two consecutive seal years, provided both are valid).

Natural gas meters

  • manufacturer and model, unless otherwise authorized in accordance with section A.1.1;
  • same or similar capacity rating, unless otherwise authorized in accordance with section A.1.1;
  • measurement functions (e.g. measured quantities, temperature/pressure conversion);
  • firmware version, unless otherwise authorized in accordance with section A.1.1;
  • same model or type of telemetering device or auxiliary attachment (if so equipped), unless otherwise authorized in accordance with section A.1.1;
  • status at time of last inspection (i.e. new, renewed or reserviced);
  • seal year (same seal year or two consecutive seal years, provided both are valid).

A.1.1 Forming lots with mixed meters

Where a lot includes meters which, for the purposes of lot homogeneity, are ones which possess a similar characteristic rather than a characteristic which can be readily identified as being the same, meter owners are responsible for maintaining documented records identifying the similarities which support the homogeneity conclusion (as concerns including these meters within the subject lot).

For the purposes of compliance sampling, if an accredited organization wishes to combine in one lot various models or vintages of meters and/or meters equipped with and without a telemetering device, the accredited organization must submit a request to MC with accompanying documentation in support of their claim that these differing meters can be considered homogeneous.

A.2 Sample homogeneity requirements

The meters in a sample must be homogeneous with respect to similar time in usage. For a sample meter to be considered homogeneous with regard to similar time in use, a meter must have been in service for a time period that meets or exceeds the applicable time on test requirements of Annex E.

Note: Where nmin is not achieved with regard to this criteria, a meter owner may re-form the lot or reduce the seal period extensions available as per section 5.7.

Annex B (normative)—Minimum to maximum sample sizes

Table B.1: Minimum (nmin) to maximum (nmax) sample sizes
n min n max
30 37
42 52
44 55
65 81
80 100
125 156
200 250
315 394

Annex C (normative)—Single sampling plans

Table C.1: Single sampling plans indexed by limiting quality
Lot size2 Limiting quality (LQ)1
3.15
(Level 1)		 5.0
(Level 2)		 8.0
(Level 3)		 12.5
(Level 4)		 20.0
(Level 5)
nmin, Ac type 1, Ac type 2
Up to 500 80, 0, 0 65, 0, 0 not
available 3		 not
available 3		 not
available 3
501 to 1 200 125, 1, 1 80, 1, 0 65, 1, 0 42, 2, 0 42, 4, 0
1 201 to 3 200 125, 1, 1 125, 3, 1 80, 3, 0 65, 4, 0 65, 8, 0
3 201 to 10 000 200, 3, 3 200, 5, 3 125, 5, 1 80, 5, 1 80, 10, 1
10 001 to 35 000 315, 5, 5 315, 10, 5 200, 10, 3 125, 10, 3 125, 18, 3
over 35 000 not available not available 315, 18, 5 200, 18, 5 200, 32, 5
Table C.2: Small lot size plan with increased sampling frequency
Lot Size Limiting quality (LQ)1
5.0
(Level 1) 4		 8.0
(Level 2) 4		 12.5
(Level 3) 4		 20
(Level 4) 4
nmin, Ac type 1, Ac type 2
Up to 500 44, 0, 0 44, 1, 0 44, 2, 0 44, 4, 0
Table C.3: Very small lot size plan
Lot size Limiting quality (LQ)1
(nonconforming)
5.0
(Level 4)
nmin, Ac type 1, Ac type 2
Up to 60 30, 0, 0

Annex D (normative)—Maximum seal period extension levels

Table D.1: Maximum seal period extension levels
Ordinal sampling occurrence Maximum seal period extension level
1st Level 1
2nd Level 2
3rd Level 3
4th
(and higher)		 Level 4

Annex E (normative)—Time on test requirements and maximum seal period extensions

Table E.1: Time on test requirements and maximum seal period extensions
Initial reverification period (in years) 1st extension (in months) Subsequent extension 5 Maximum seal period extension (in years)
New or renewed meters Reserviced meters Level 1 Level 2 Level 3 Level 4
12 115 90 75% 10 8 5 2
11 105 81 75% 9 7 5 2
10 84 68 70% 8 6 4 2
9 75 59 70% 7 5 3 2
8 67 51 70% 6 4 3 2
7 58 42 70% 5 4 2 1
6 50 34 70% 4 3 2 1
5 42 26 70% 0 (no extension) 3 2 1

Footnotes

Footnote 1

As per 5.5.3, unless otherwise stated in the applicable reverification specification of the subject meter type or class:

  • type 1 (C1) > 2.0%;
  • type 2 (C2) > 2.9%.

Return to first footnote 1 referrer

Footnote 2

Maximum permissible lot size is 35 000.

Return to first footnote 2 referrer

Footnote 3

Move down targeted level column to the criteria for lot size of 501 to 1 200.

Return to first footnote 3 referrer

Footnote 4

Seal period extension as per 5.6 (e).

Return to first footnote 4 referrer

Footnote 5

For subsequent extensions, the time on test (rounded up to the next whole month) is based on indicated percentage multiplied by the previous extension.

Return to first footnote 5 referrer

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