Detachable charging cables part of SAE J3400 Recommended Practice

The second version of SAE J3400, titled North American Charging System (NACS), is now being published as an SAE Recommended Practice. This version consolidates the requirements for electric vehicles (EVs) and Electric Vehicle Supply Equipment (EVSE) into a single document. This represents a critical advancement for the industry as it responds to a growing need for standardized practices during a pivotal moment in the adoption of electric vehicles.

In February 2023, the Federal Highway Administration (FHWA) issued a final rule for National Electric Vehicle Infrastructure Standards and Requirements under the Bipartisan Infrastructure Law. The rule stated that the Combined Charging System (CCS) Type 1 connector would be required for each Direct Current Fast Charger (DCFC) port, aligning with what was seen as the industry standard. However, just months later, Ford made a significant announcement in May 2023, declaring the company’s intention to adopt NACS, followed by other automakers. This shift prompted the SAE to lead the effort to develop NACS as a standardized practice, with support from Tesla and the Joint Office of Energy and Transportation.

The timing of these developments has been crucial. Many experts, including those at BloombergNEF, have identified this period as an inflection point for EV adoption. The need for adaptable and responsive industry-led standards is critical as new technologies scale, and NACS has provided an opportunity for substantial improvement and change within the EV charging infrastructure.

Several independent efforts have contributed to the ongoing standardization of NACS. For instance, three U.S. national laboratories founded the ChargeX Consortium, aimed at improving the EV charging experience and addressing charging reliability and usability issues. Public Key Infrastructure is also being improved to allow EVs to charge across networks without a single company controlling the trust model. Additionally, the SAE Truck and Bus Council’s Electrical Systems Committee is revising SAE J3068 to accommodate portable cable assemblies for more flexible charging.

New elements have been introduced in SAE J3400 to enhance EV charging standards. These include requirements for DC connectors to pass new conformance tests with thermal sensing capabilities, preventing charging interruptions by detecting when EVs and EVSE are near their thermal limits. The standard also recommends implementing arc detection systems to increase the life of connectors and improve reliability. Furthermore, support for both AC and DC bidirectional power flow, tied to existing standards, is emphasized in the new document.

Tesla’s NACS equipment already features arc detection, which identifies voltage and current anomalies that can cause arc formation, such as from excessive side loads on the cables. These measures help extend the lifespan of connector contacts and provide early warnings for when maintenance is needed.

Building on prior discussions of SAE J3400 and advances in AC charging, the revised SAE J3400 and SAE J3068 standards encourage the broad deployment of shared-use EVSE systems with detachable cable assemblies. This approach provides clearer technical guidelines and supports the integration of renewable energy, addressing the challenges of mass electrification while reducing system costs.

The NACS Task Force, led by industry experts from various sectors, will continue to revise the standard to ensure responsive and innovative solutions for EV power transfer, ensuring compatibility and reliability across manufacturers and products.