When Tesla coined the term NACS, it stood for North American Charging Standard. But it was not then nor has it yet become a “standard” in the way that so many other vehicle design and safety protocols have been codified by the Society of Automotive Engineers. But it just began its official journey to becoming a standard, when the SAE released its J3400 EV Coupler Recommended Practices document on October 8. This document serves to guide companies and engineers building charging infrastructure and integrating NACS charging into vehicles.
As this process progresses over the coming months opportunities for improvement may arise, and these will be baked into a final standard expected to be issued at the end of this year. We were on hand at the press event and had a long chat with one of the authors, Dr. Rodney McGee, chairman of the SAE J3400 NACS Task Force. Wow, did we have a lot to learn about the plug Tesla designed.
NACS Was Vastly Superior From the Start
As a vehicle charging protocol developed by an EV startup that was simultaneously investing to build both the cars and the infrastructure to support them, NACS was in a unique position to become an optimized ecosystem capable of handling more voltages and charging types. By comparison, the J1772 standard was primarily developed with legacy automakers new to electrification, not at all invested in the charging infrastructure side, and accustomed to outsourcing peripheral tasks like this to suppliers. This explains how the J1772 connector modified to CCS specs for DC fast charging resulted in such a clunky connector and cable. Now that legacy OEMs are investing in the Ionna charging network, they can more fully appreciate how NACS is more inherently infrastructure friendly.
NACS Is More Aware
Today if you have a simple ground-fault interruption of your home charger with a Tesla, thanks to its digital communications protocol, both the car and the charger know and report what the problem is. With any other car using J1772’s analog comms, that info isn’t known or shared, so you go to the dealer. They start hunting for the problem and possibly swapping parts.
Superior Diagnostics
The Federal Highway Administration convened the National Charging Experience Consortium (ChargeX) in May 2023, which has developed a roster of error codes for public EV chargers to communicate, and those are built in to J3400. For example, if the cord-to-vehicle lock isn’t responding, that’s an indication the end of the cord may have been cut off (something many chargers previously had no way of detecting and reporting).
Bring Your Own Cable
In most of the world, the Level 2 charging infrastructure presents a socket, and you bring your own cord with which to charge your car. Locking your doors locks both ends of the cord to prevent theft.
This greatly simplifies the infrastructure, more easily allows for streetside lamppost charging, and McGee suggests this is the best way to provide charging for apartment dwellers. And it’s supported by J3400, using the European standard infrastructure-side plug.
1MW Charging Supported
J3400 covers up to 1,000-volt charging at current flow rates up to 900 amps when cooling is provided only on the charger side, or 1,000 amps when both the charger side and the vehicle socket are cooled (no production EV has cooled charge ports yet).
220/277—Whatever It Takes
One of Tesla’s more brilliant moves was making its connectors capable of AC charging on either residential 208–240-volt power or the 277-volt power that comes in with a commercial building’s three-phase 480-volt feed. So businesses interested in providing AC charging for employees didn’t have to invest in transformers; the voltage gets altered onboard. This was crucial to controlling the cost of building out the Supercharger network, and J3400 preserves this. SAE estimates that around half of commercial/urban sites would pay about double for an Level-2 charging installation for J1772 vs SAE J3400. (It’s also important, given today’s soaring cost and shortage of transformers.) That higher voltage speeds charging and lowers amperage, and because electrical losses increase with the square of current, charging at 277 volts versus 208 can reduce losses in the wiring by 50 percent.
Three-Phase 52-kW AC Charging
The global infrastructure-side plug for bring-your-cord applications, covered in J3400, incorporates a couple extra pins that will support 480-volt three-phase AC charging that could be important to medium-duty fleet customers, saving them the expense of installing DC fast chargers. This requires a different plug on the vehicle end (J3068 medium/heavy-duty), but with that connector trucks could also then power both 120V and 240v loads just like your generator does—great for powering a big job site or disaster recovery area. McGee advocates for bigger pickups and medium duty trucks switching to these J3068 plug for exporting power (as opposed to, say the NEMA 14-50 plug currently in the F-150 Lightning cargo box), because the SAE J3068/2 document describes a way to negotiate and provide for different loads as needed.
J3400 Encourages AC Charging
The NACS protocol makes it cheaper and easier to add AC charging to more workplaces, and to offer much wider availability of bring-your-cord public charging. McGee explains why society needs this: “We want cars to be able to be plugged in when they’re parked so that they can absorb the extra wind and solar during the day so [drivers] can get the cheapest charging.” Cheapest ends up being most green, and as bi-directional charging becomes more prevalent, the grid will be able to store surplus green power and draw from this vast stored-energy reserve during periods of peak demand. Otherwise, if apartment-dwelling commuters must rely on DC fast charging during peak travel times, we WILL need to install a bunch more power-generation.
