Electric Vehicle Fueling FAQs

 Also referred to as Electric Vehicle Supply Equipment (EVSE), these devices vary considerably in both performance and design. Equipment is categorized by its use of alternating current (AC) or direct current (DC) and its maximum power output, measured in kilowatts (kW).  These factors result in a classification of charging “levels” that correlate to the rate the equipment can deliver an electrical charge.  AC Level 1 EVSEs are mostly limited to residential use and require an extended period of time (18 or more hours) to fully charge an EV battery from a low level of charge. AC Level 2 EVSEs are capable of fully charging an EV battery over several hours, while Level 3 EVSE (DC Fast-Chargers) can provide a full charge in well under an hour. 

Commercial fueling systems are rated to deliver power levels in the range of approximately 22 kW to 500 kW.  Charging systems are equipped with types of connectors that meet defined standards specified for AC or DC charging.  Various types of connectors are used throughout the U.S., including the Combined Charging System connectors (CCS1 and CCS2), the North American Charging Standard (NACS), the SAE J1772 (“J plug”) and the CHAdeMO connector, which is a common DC fast connector type among Japanese automakers.

The U.S. Department of Energy's Alternative Fuels Data Center provides further information regarding EV Charging Infrastructure. 

If you have a complaint and/or inquiry, you may contact your State Weights and Measures program for assistance. Please see the list of State Directors for more information. 

You may also directly contact the business and/or operator responsible for the EV charging station. Most public EV chargers have a customer service number and/or 24/7 online support available. 

NIST Handbook 130 Uniform Laws and Regulations in the Areas of Legal Metrology and Fuel Quality, IV. Uniform Regulations, Part B. Uniform Regulation for the Method of Sale of Commodities, Section 2.33. Retail Sales of Electricity Sold as a Vehicle Fuel specifies the kilowatt-hour (kWh) as the official unit of measure for sales of electricity to fuel electric vehicles.  This section was amended in 2023, removing the megajoule (MJ), which was initially recognized along with the kWh as a traceable unit of measurement for the delivery of electricity when sold to fuel electric vehicles; however, the unit was not commonly used globally in the marketplace. Requiring electrical energy to be sold by $/kWh (unit price) based on the amount of energy actually delivered to an EV helps ensure that consumers can make equitable price and value comparisons across various stations and/or conditions for each charging session.

Yes. At present, a variety of methods for energy pricing via EV charging services can be found within every state, and some are based on quite different measurement units. For example, energy pricing structures can range from $/kWh to $/time connected (min, hour), flat fees for individual connection sessions, and may include additional fees for parking or membership.

Please see Section 3.2 of NIST SP2200-03 An Evolving Regulatory Landscape for Commercial Electric Vehicle Fueling for more information.

NIST Handbook 130 requirements in IV. Uniform Regulations Part B. Uniform Regulation for the Method of Sale of Commodities Section 2.33. Retail Sales of Electricity Sold as Vehicle Fuel established the kilowatt-hour (kWh) unit of measurement as the basis for sales of electricity when sold as a vehicle fuel and for related billing, labeling, and advertising requirements.  This requirement was first established in 2012 for EVSEs and then published in the 2013 edition of NIST Handbook 130.

NIST Handbook 44 requirements form the basis for type evaluation under the National Council on Weights and Measures National Type Evaluation Program and for routine inspection and test procedures to determine if equipment used in commercial electric vehicle fueling applications comply with these standards. Specifically, NIST Handbook 44 Section 1.10 General Code, Section 3.40 Electric Vehicle Fueling Systems Code, and 5.55 Timing Devices (applicable for systems that have the capability to assess time-based fees associated with an electric vehicle charging session, such as parking) provide specifications, tolerances, and other technical requirements for devices used for the measurement of electricity dispensed in commercial vehicle fuel applications.

Section 1.10 General Code applies to all device types and is broad rather than device-specific. Standards in this section may cover features or situations that may not exist in the device codes and are equally as important as the device codes.

Section 3.40. Electric Vehicle-Fueling Systems was added to NIST Handbook 44 as a “tentative code” in 2015. In July 2022, the status of the code was changed from “tentative” to “permanent” effective January 1, 2023.

Section 5.55 Timing Devices was modified in 2015 to recognize equipment used to assess fees for time-based services, in addition to the cost of supplying electrical energy, by providing separate standards for the time feature.

NIST Handbook 44 specifies the permissible accuracy level or applicable tolerance based on whether the device is designed to deliver alternating current (AC) or direct current (DC).  Additionally, for DC devices, tolerances apply based on the date the equipment is placed in commercial use.  Tolerances are defined as “A value fixing the limit of allowable error or departure from true performance or value.”

Based on the most recent edition of NIST Handbook 44, Section 3.40. Electric Vehicle Fueling Systems, tolerances applied to EVSEs:

For AC EVSEs, the acceptance tolerance is ± 1%, and the maintenance tolerance is ± 2% of the measured energy delivered by the device.

For DC systems placed in service prior to January 1, 2025, and marked with an accuracy Class 5, the tolerance is ± 5% of the measured energy delivered by the device. Note that all DC EVSEs are exempt from this requirement until January 1, 2028.    Paragraph G-A.3. Special and Unclassified Equipment exists for use by jurisdictions wishing to inspect and test existing DC systems in order to approve this equipment for commercial use. 

For DC systems not marked with an accuracy Class 5 or that are placed in service on or after January 1, 2025, the acceptance tolerance is ± 1% and the maintenance tolerance is ± 2% of the measured energy delivered by the device.

The tolerances applicable to the performance of the integral timing element in this equipment used to assess time-related services associated with the electrical energy charging session are prescribed in NIST Handbook 44 Section 5.55 Table T.1.3. Maintenance and Acceptance Tolerances for Parking Meters and Other Timing Devices Used to Assess Charges for Parking.  Table T.1.3. does not permit time to be indicated in excess of the actual time elapsed, and the allowable error in the indication of time resulting in less than the actual passage of time is applied based on 30-minute segments of time that elapsed during the entire time-based service.  The tolerances in this code are not applicable to the delivery of electrical energy to the electric vehicle and not all EVSEs are of a design that includes a timing element for this purpose.  

The legal metrology requirements in the NIST Handbooks 44 and 130 were developed by the U.S. National Work Group (USNWG) for Electric Vehicle Fueling and Submetering. The USNWG was formed in 2012 to develop requirements for commercial electricity-measuring devices (i.e., residential sub-metering, electric vehicle dispensers) to ensure that the prescribed methodologies and standards facilitate measurements that are traceable to the International System of Units (SI). This group is comprised of stakeholders from private industries, standards organizations, and state and federal government. The recommendations developed by the USNWG adhered to the weights and measures standards development process through the National Conference on Weights and Measures (NCWM) and for inclusion in the NIST Handbooks 44 and 130.

Yes, if the fee is properly disclosed. Electricity as vehicle fuel can only be sold by the kilowatt-hour (kWh). An EVSE cannot sell electricity as vehicle fuel by units of time (e.g., by the second, minute, or hour) elapsed during the charging session.  

An additional fee can be charged for the time spent in the space a vehicle must occupy to connect to the EVSE or some other period of time such as an overstay after the EV is fully charged or other fees in direct connection with fueling of the vehicle (NIST Handbook 44 Section 5.55 Timing Devices).