The number of electric vehicles (EVs) on the market — and on the road — continues to increase. Drivers need sufficient infrastructure to charge EVs and alleviate range anxiety, the nagging concern that a battery is not charged sufficiently to go the distance.
To support the growing needs of the EV driving public, charging infrastructure needs to expand rapidly while focusing on safety and performance, but also addressing efficiency, reliability and interoperability. Today’s network for conductive charging is certified for compliance with safety standards, including:
- UL 2202, the Standard for DC Charging Equipment for Electric Vehicles
- UL 2594, the Standard for Electric Vehicle Supply Equipment
- UL 2251, the Standard for Plugs, Receptacles, and Couplers for Electric Vehicles
- UL 2252, the Standard for Adapters for Use with Electric Vehicle Couplers
These Standards assess risk mitigation of fire, shock and injury and outline construction requirements addressing materials used, assembly of parts, wire sizing and more. The requirements help mitigate specific safety risks that can be addressed through design. Standards also include testing requirements regarding performance in both normal and abnormal or fault conditions to demonstrate that a design does not lead to an increased risk of fire, shock or injury.
Additionally, these Standards include requirements for marking and instruction for proper use, maintenance and service, as well as warnings for specific concerns. While vehicle charging options are expanding, connector compatibility issues can still be a roadblock. Adapters can facilitate charger compatibility if charging can progress unimpeded. UL 2252 evaluates compatibility and how the adapter can help mitigate safety risks.
However, these Standards don’t address other aspects that are important to drivers, including efficiency, reliability and functional interoperability. Let’s look at each of these in depth.
Efficiency – Power loss in charging cables and components isn’t addressed through safety Standards, as long as no fire or shock hazard develops during power transfer. Rather, overall energy efficiency is addressed through ENERGY STAR®, a program managed by the U.S. Environmental Protection Agency. However, the program has recently been the subject of discussions about potential budget and staffing reductions.
Reliability – Lack of reliability can be caused by equipment malfunction, interoperability issues between the vehicle and charger, or even physical causes such as damage or vandalism. Specific design aspects can be utilized to attempt to address known reliability issues, such as providing cable management systems that prevent the connector and cable from contacting the ground, causing damage. Design aspects related solely to reliability are optional. From the perspective of safety standards, if a charger will not turn on, it is not a noncompliant result. Failing to operate — but doing so in a safe manner — is generally acceptable according to the safety standards for EV charging equipment. From a user perspective, unreliability is frustrating, but not a safety risk.
Interoperability – UL Standards address the physical interoperability of EV couplers that connect the charger and the vehicle. Functional interoperability addresses the ability of the charger to work with any vehicle that is connected to the charger. There is a lot of information shared between the vehicle and the charger during a charge session. That exchange of data must be seamless, or the charger or the vehicle may assume there is an error and abort the charge session. Although to the user this may appear as if the charger is unreliable or unable to work with the vehicle, it is actually a safety mechanism that prevents the charger from operating if it is not 100% certain that a vehicle is connected and that all proper functional handshakes have occurred.
Interoperability is addressed in some standards and is increasingly gaining notice, but it was not included in safety standards for two reasons. First, if the charger will not turn on because of interoperability issues, the charger still complies with the documented requirements. This is more of a functionality or user experience issue than a safety issue. Second, interoperability requires two separate entities to agree on requirements and work together. The EV charger safety standards address the infrastructure piece only, and do not address the vehicle. While the UL Standards for infrastructure address worst-case physical operating modes, they do not contain requirements for the vehicle and cannot fully address functional interoperability for the combination.
The concepts of reliability and interoperability are important to EV drivers, although they may not be using those specific terms. When an EV charger is unavailable to a driver for any reason, this results in a disappointing experience.
UL Standards provide the foundation for safer EV charging infrastructure. When stakeholders, including EV manufacturers and makers of charging equipment, collaborate, the user experience will also be improved through greater efficiency, reliability and interoperability.
