Electric Vehicle Fueling and Submetering: U.S. National Work Group on Measuring Systems

Electrical Energy:  U.S. National Work Group

The U.S. National Work Group (USNWG) formed in August 2012, to develop proposed requirements for commercial electricity-measuring devices (including those used in sub-metering electricity at residential and business locations and those used to measure and sell electricity dispensed as a vehicle fuel) and to ensure that the prescribed methodologies and standards facilitate measurements that are traceable to the International System of Units (SI). This work is not intended to address utility metering in the home or business where the electricity metered is consumed by the end purchaser and that falls under the authority of entities such as the local utility commission.

The USNWG will review and propose changes as needed to:

1. Draft requirements for equipment used to measure and sell electricity in commercial applications for possible inclusion in NIST Handbook 44 (HB 44), ''Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices''; and
2. Draft procedures for type evaluation, laboratory, and field testing of equipment for possible inclusion in NIST Examination Procedure Outlines and other procedure documents.

Included among the topics to be discussed by the USNWG for current and emerging device technologies used in commercial electric measuring systems are: (1) Method-of-sale requirements; (2) metrology laboratory standards and test procedures; (3) uncertainties; (4) measurement traceability; (5) tolerances and other technical requirements for commercial measuring systems; (6) existing standards for testing equipment; (7) field implementation; (8) data analysis; (9) field test and type evaluation procedures; (10) field enforcement issues; (11) training at all levels; and (12) other relevant issues identified by the USNWG.

The USNWG's technical output may result in the revision of current standards or the development of new standards for testing equipment, including documents such as the NIST Handbook 105 Series: Specifications and Tolerances for Reference Standards and Field Standard Weights and Measures available on the NIST OWM Publications and Documentary Standards website; NIST HB 44: Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices, and NIST Examination Procedure Outlines (EPO), as well as proposed changes to requirements and testing procedures for commercial devices and systems used to assess charges to consumers for electric vehicle fuel.

Of Interest

USNWG Restructures

On August 26, 2016, the USNWG agreed to modify its June 2013 version of Operational Guidelines to restructure into two subgroups to better address the two commercial equipment applications within the work group’s scope: (1) Electric Vehicle Fueling Equipment (EVFE) (aka Electric Vehicle Fueling Systems (EVFS), Electric Vehicle Supply Equipment (EVSE) or Electric Vehicle Chargers) and (2) Watthour Type Electric Meters (WHE).

EVSE DRAFT Examination Procedure Outline (EPO)

In December 2015 Draft EPO 30 was distributed as a starting point for the Test Procedure Subcommittee and EVSE Subgroup discussions. An EPO includes the minimum recommended procedures to be used in official inspection and testing of commercial weighing and measuring equipment. The EPO is intended for routine test and inspection of an EVSE by officials/service industry to compliance with HB requirements. NIST developed EPO 30 based on device design, performance, test, operation requirements in NIST Handbook 44 Sections 1.10. General Code, 3.40. Electric Vehicle Fueling Systems – Tentative Code, and 5.55 Timing Devices. Please note that no meeting date has been established for the start of discussions about Draft EPO 30.

EVSE NTEP

The National Conference on Weights and Measures (NCWM) National Type Evaluation Program (NTEP) began accepting applications for Alternating Current (AC) systems November 1, 2021.  NCWM Publication 14 Checklist for EVSE devices is based on NIST Handbook 44 Sections 1.10, 3.40, and 5.55.

Development of International Standards: During the October 2016 15th International Conference of the 51st International Committee of Legal Metrology (CIML) a new project in Technical Committee (TC) 12 Instruments for measuring electrical quantities was approved, for the revision of Recommendation (R) 46 (2012) Active electrical energy meters to address new and different technology and applications.  Initial work on an international document on electric vehicle supply equipment (EVSE) requirements and test procedures was done as part of the revision process for R 46.  This effort was subsequently split off into a separate new project group established in October 2021 under TC 12 Project (p)3 Electric vehicle charging stations.  The TC 12 p3 was fast tracked to develop for publication a self-contained OIML Guide for EVSE that is separate from R 46. A separate OIML publication for EVSEs allowed the project group to fully address the unique aspects of the electric vehicle charging application, such as the direct sales nature of transactions, means of conveying the measurement result, and typical progressions of current levels over time.

The TC 12 p3 began work in November 2021 resulting in the publication of OIML Guide (G) 22 Electrical Vehicle Supply Equipment in September 2022.  Guide 22 is based on R 46 and is intended to address built for purpose systems which incorporate AC or DC energy metrology whether that metrology is accomplished by using a separate type approved meter or one that is integrated into the electronics of the EVSE.    The Guide does not apply to wireless charging systems. 

OIML TC 12 p3 began discussions on the scope of revisions to OIML G 22 necessary to develop a full Recommendation document that is more fine-tuned with further elaboration on the text in G 22 and to include all mandatory parts.  The TC 12 p3 met early in June 2023 in Delft, the Netherlands.  At the OIML G 22 meeting the project group indicated it is seeking to progress rather quickly on  the development of a First Committee Draft Recommendation. This will hinge, however, on the revision of the software components of the document, which currently derive from a 2008 version of D 31 General requirements for software-controlled measuring instruments, which was revised in 2019 and is on track for publication of a new revision in  2023. A subgroup will undertake these revisions and they will then be combined with the G 22 (2022) document.

R 46 and G 22 CONTACT
Katya Delak - katya.delak [at] nist.gov (katya[dot]delak[at]nist[dot]gov)

For the latest on the development of G 22 Electrical Vehicle Supply Equipment by TC 12 p3 is also available on the OIML website at: www.oiml.org.