E-37—Processing multiple customer metering systems under S-S-06—Sampling Plans for the Inspection of Isolated Lots of Meters in Service
Revision number: N/A
Table of contents
- 1.0 Purpose
- 2.0 Scope
- 3.0 References
- 4.0 Definitions
- 5.0 Policy decisions
- 6.0 Policy interpretations
- 6.1 Lot formation
- 6.2 Lot homogeneity
- 6.3 Sample selection
- 6.4 Sample selection criteria
- 6.5 Sample selection qualification
- 6.6 Meter sampling records
- 6.7 Quality characteristics
- 6.8 Acceptance criteria
- 6.9 Meter performance testing and limits
- 6.10 Seal extension periods
- 6.11 Reverification date calculations
- Appendix: Example of multi-sample selection and testing process
This bulletin provides policy decisions and interpretations, and sets criteria for accredited service providers and registered contractors (meter owners) with respect to the processing of multiple customer metering systems (MCMSs) under sampling specification S-S-06.
This bulletin applies to all design types of multiple customer metering systems used for the purpose of establishing the basis of a charge for electricity and submitted for compliance sample testing.
- S-01—Implementation Guide for the Application of Statistical Sampling Requirements
- S-S-01—Specifications for Random Sampling and Randomization
- S-S-02—Measurement Uncertainty and Meter Conformity Evaluation Specifications
- S-S-03—Prerequisites to the Use of Sampling Inspection
- S-S-06—Sampling Plans for the Inspection of Isolated Lots of Meters in Service
- S-E-02—Specifications for the Verification and the Reverification of Electricity Meters
- S-E-04—Installation Requirements for Multiple Customer Metering Systems
- Compliance sampling (échantillonnage de conformité)
Specialized form of acceptance sampling of isolated lots of meters in service, having the object of ensuring that lots of unacceptable quality have a high probability of rejection.
- Integrated system (système intégré)
Multiple customer metering system approved for use with external sensors which are considered to be integral to the meter at the time of verification. These systems typically have a nameplate current rating of 100 A or greater.
- Non-integrated system ((système non intégré))
Multiple customer metering system approved for use with separately approved instrument transformers which are not considered to be integral to the meter at the time of verification. These systems typically have a nameplate current rating from 80 mA up to 5 A.
- Multiple customer metering system ((système de mesurage à clients multiples))
A system that requires on-site central processing of metrological information for more than one metering point.
- Sensor ((capteur))
Device that can measure voltage or current and that is typically used with integral systems, where each sensor is mated to a specific meter input.
5.0 Policy decisions
5.1 Qualification for sampling
In order for a system to qualify for compliance sampling under specification S-S-06, it must:
- have been initially verified and sealed under Measurement Canada's specification S-E-02.
- have been initially inspected and sealed under Measurement Canada's specification S-E-04.
- have valid seals which are applicable to both specifications.
5.1.1 Re-inspection requirements
Systems which have been modified, repaired or upgraded are to have been re-inspected and resealed as required under section 9.3 of S-E-04.
5.1.2 Record of inspection
A certificate is issued to the meter owner for the completed S-E-04 inspection of each system identified in the lot.
6.0 Policy interpretations
6.1 Lot formation
Refers to section 5.1 of S-S-06.
When processing multiple customer metering systems under S-S-06, lots are to be formed from systems that are considered homogeneous with respect to the requirements identified in Annex A of S-S-06. The following lot homogeneity requirements also apply.
6.2 Lot homogeneity
Refers to criteria of A.1 of Annex A, S-S-06.
Where applicable, the systems in the lot are to be homogeneous with respect to the following additional characteristics:
- The lot must be formed using systems of the same manufacturer and model. Additionally, the lot is to be formed from integrated systems or non-integrated systems, but not both.
- For integrated systems, the lot must also be formed using voltage or current sensors of the same manufacturer, make and model, unless otherwise authorized in accordance with clause A.1.1 of S-S-06.
- The lot must be formed using the same voltage or voltage range, unless otherwise authorized in accordance with clause A.1.1.
- The lot must be formed using the same configuration/form, unless otherwise authorized in accordance with clause A.1.1.
6.3 Sample selection
Refers to sections 5.2.1 and 5.2.2 of S-S-06.
Sample selection will be based on the unsorted lot listing of homogeneous systems.
- All qualified metering points associated with each system chosen for sampling will be assessed for conformity to S-S-06.
- All systems in the sample group will be tested until nmin has been reached.
6.4 Sample selection criteria
Refers to section 5.2.3 of S-S-06.
Meter owners are responsible for ensuring that the systems included in the sample are currently installed in service. For a multiple customer metering system, this includes each individual metering point and associated sensors as applicable.
- If a system selected for sampling is not in service, then it does not qualify as part of the sample group, and section 5.2.4 of S-S-06 applies.
- If an individual metering point associated with a system selected for sampling is not connected in service, then this metering point and its associated sensors do not qualify for sample testing.
6.4.1 Metering point exclusions
Refers to sections 5.2.3 and 5.2.5 of S-S-06.
If an individual metering point and its associated sensors, as applicable, do not qualify under section 6.4 (5.2.3 b., c. and d. of S-S-06) or their performance can't be assessed under section 6.5 b. (5.2.5 of S-S-06), then the metering point is to be excluded from sample testing.
a. Such exclusions do not have an impact on nmin under section 5.2.7 of S-S-06, unless the number of individual metering point exclusions exceeds a threshold of 30% of the total number of metering points associated with the system chosen for sampling at the time of its initial verification.
When calculating whether or not the above threshold has been exceeded, standard rounding practices (e.g. 98.50 rounds up to 99) must be applied.
For example, a system originally sealed with 24 metering points (MPs) can have up to a maximum of 8 MP exclusions (24 MPs ×.70 = 16.8 MPs rounded up to 17 MPs); therefore, this system is allowed 24 − 17 or 8 MP exclusions.
6.4.2 Additional owner responsibility
Meter owners will also be responsible for ensuring that the systems that are selected as a sample:
- have not had their metrological parameters adjusted post installation;
- are homogeneous with regard to the criteria of A.1 of Annex A of S-S-06 as well as the additional homogeneity criteria identified in section 6.2 of this bulletin;
- meet the total time on test criteria of A.2 (Annex A) of S-S-06, which includes each individual metering point associated with the selected metering systems.
6.5 Sample selection qualification
Refers to section 5.2.4 of S-S-06.
- a. Where a system does not qualify for inclusion in the sample as per the requirements of 6.4 (5.2.3 of S-S-06), meter owners will exclude this system as part of the sample group for performance testing purposes and replace it with the next sequential system on the preselected unsorted sample system listing that meets the applicable criteria. The exclusion rationale for the subject system will be reported as per the requirements of 5.3.4 of S-S-06.
Refers to section 5.2.5 of S-S-06.
- b. Where the performance of a system which has been removed from service can't be assessed in accordance with the requirements of this document, the meter owner must replace it with the next sequential system on the preselected unsorted sample listing of systems available for testing. All systems and their associated test results will be included, unless a good reason for exclusion is identified and reported as per the requirements of 5.3.4 of S-S-06.
Refers to section 5.2.6 of S-S-06.
- c. Systems which have been excluded as samples as a result of not satisfying either 6.4 (5.2.3 of S-S-06) or 6.5 b. (5.2.5 of S-S-06) will not be returned to the parent lot.
6.6 Meter sampling records
Refers to section 5.3 of S-S-06.
All sample systems selected but not included in the final calculations must be accounted for by the meter owner and the reasons for exclusion must be documented and made available on request for Measurement Canada's review. Evidence of deliberate exclusion or improper accounting may disqualify the results of the sample's analysis.
6.6.1 Individual metering point exclusions
In the case of a multiple customer metering system, this includes any exclusion involving individual metering points and associated sensors (as applicable), as per section 6.4 (5.2.3 of S-S-06).
6.7 Quality characteristics
Refers to section 5.4 of S-S-06.
Each defective system excluded from the final calculations will be preserved for Measurement Canada's review and will be the subject of an investigation by the meter owner to determine the cause of the defect(s). In the case of defective systems, a report will be prepared and must include the following information associated with the investigation.
6.7.1 Exclusion from calculations
In the case of a multiple customer metering system, exclusions from the final calculations may also include any individual metering points and associated sensors (as applicable) found to be defective.
6.8 Acceptance criteria
Refers to section 5.5 of S-S-06.
With respect to a multiple customer metering system, the term "meter" in this section refers to the system and includes all individual metering points and associated sensors, as applicable.
6.8.1 System acceptance criteria
Each system which has been selected as a sample can be considered accepted if each of the four conditions (a., b., c. and d.) identified in section 184.108.40.206 of S-S-06 have been met.
6.9 Meter performance testing and limits
Refers to section 5.5.3 of S-S-06.
All performance tests must be conducted as per the reverification specifications applicable to the subject system type, class and configuration.
6.9.1 Performance testing criteria
In the case of a multiple customer metering system, the number of Type 1 (C1s) and Type 2 (C2s) meters to be counted will be based on the performance test results of each qualified individual metering point associated with the systems selected for sampling.
6.9.2 Performance testing limits
The results of all performance testing for each system selected for sampling must be assessed against the limits identified in section 220.127.116.11 of S-S-06 for marginally conforming metering points and section 18.104.22.168 for nonconforming metering points. In addition, for the purpose of section 6.6 (22.214.171.124 of S-S-06), a Type 2 (C2) nonconforming meter is also counted as a Type 1 (C1) marginally conforming meter.
6.10 Seal extension periods
Refers to Annex E of S-S-06.
In the case of a lot of multiple customer metering systems assessed under S-S-06, where the seal period extension is granted under Annex E, the extension will be applied to all systems identified in the parent lot listing, excluding any systems identified under section 6.5 (5.2.6 of S-S-06).
Individual metering points excluded from performance testing under section 6.4 will remain as part of the parent lot when applying the seal extension period, unless their exclusion is attributable to a defect as identified under section 6.7.1 (5.4.3 of S-S-06).
6.11 Reverification date calculations
Refers to section 5.8 of S-S-06.
Any reference to meters in section 5.8 of S-S-06 is considered to be a reference to systems with respect to the reverification date calculations.
Appendix: Example of multi-sample selection and testing process
- Homogeneity assessment has established that 600 systems qualify for sampling. All systems were originally verified and sealed with 12 metering points (MPs) each. According to Table 2 of Annex C of S-S-06, the lot size falls within the range of 501 to 1,200.
- Using a targeted limiting quality of 3.15, Table 2 identifies nmin to be 125 systems. According to Table 1 of Annex B, nmax is determined to be 156 systems. A random sample must be generated based on the lot listing for an nmax of 156 systems.
- Time on test according to Annex E of S-S-06 is 84 months, based on a 10-year initial reverification period.
- The number of MP exclusions allowed per system is (12 x 0.7 = 8.4 MPs) rounded down to 8 MPs; therefore, the maximum number of exclusions allowed is 12 – 8 or 4 MPs.
- Review of the 156 systems selected for sample testing has determined the following:
- Total number of potential MPs available for testing is 156 systems × 12 MPs / system = 1,872 MPs;
- 1 system found not to be installed in service; system excluded, nmax reduced by 1;
- 3 systems found not to meet time on test criteria; systems excluded, nmax reduced by 3;
- 1 system found with 6 out of 12 MPs not installed in service (exceeds 30% threshold); therefore, the system was excluded, nmax reduced by 1;
- 4 systems found with 2 MPs, each not installed in service (within 30% threshold); therefore the systems are not excluded from sample group, but 8 MPs are to be excluded from testing and nmax unaffected;
- 4 systems with 1 MP each not meeting time on test criteria (within 30% threshold); therefore, systems not excluded from sample group, but 4 MPs are to be excluded from testing and nmax is unaffected.
- As a result of the above exclusions, nmax has been reduced by 5 systems, the number of available systems which remain is 151. Total number of MPs available for testing has been reduced by (5 systems × 12 MPs) + (4 systems × 2 MPs) + (4 systems × 1 MP) = 72 MPs; therefore, the total MPs to be assessed is 1,800: (156 systems × 12 MPs per system) – 72 MP exclusions.
- The remaining 151 qualified systems and their associated 1,800 MPs will be inspected until nmin (125 systems) is reached.
- Conformity assessment under Annex C of S-S-06 must be carried out based on the performance test results of each qualified system and its associated MPs in conjunction with the number of C1s and C2s allowed for a given lot size and the targeted limiting quality selected.
- It was determined from the performance testing that 1 C2 and 3 C1s were discovered. According to Annex C of S-S-06, the lot failed to meet the level 1 criteria; however, moving diagonally downward on the table, following the nmin value of 125 we see that the lot does qualify for a level 2 extension.
- According to Annex E of S-S-06, since the lot had received a 10-year initial reverification period, it will be granted an extension of 6 years for meeting level 2.
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