The Evolution of EV Charging Standards: From SAE J1772 to ISO 15118

History of EV Charging Standards: An Overview

The evolution of EV charging standards is, at its core, a story of solving persistent design and compatibility problems.

Early connectors couldn’t communicate reliably with every vehicle or deliver enough power, so each new standard emerged to fix a specific pain point.

As adoption accelerated, safety and communication standards became essential for preventing hazards like electrical fires and data breaches, while recent funding rules began requiring certified solutions for “Plug & Charge” security and reliability.

Understanding how these standards evolved helps hardware teams design equipment that remains compliant, attracts funding, and stays relevant as new technologies and regulations arrive.

‍

Key Points

• EV charging has progressed from the widely adopted SAE J1772 plug to the new NACS/SAE J3400 standard, with developments over the years bringing higher power and enhanced safety, and this latest standard now aims to solve interoperability.
• The DC fast-charge battle is shifting: CHAdeMO and Combined Charging System (CCS) are being eclipsed in North America as Ford, GM, and nearly all other automakers adopt Tesla’s NACS to tap its extensive Supercharger network, prompting changes to federal funding eligibility.
• ISO 15118-20 enhances features like encrypted Plug & Charge and vehicle-to-grid (V2G) communication, setting the foundation for smarter, more secure charging networks.
• Achieving true connector compatibility means multi-port hardware and firmware that can handshake across J1772, CCS1/2, NACS, and ISO 15118—raising design, certification, and maintenance demands.
• Future-proof infrastructure calls for advanced liquid-cooled cables to handle upcoming megawatt charging, adaptable communication hardware for evolving network protocols, and rigorous cyber-hardening to secure the entire charging ecosystem.

A Timeline of the History of EV Charging Standards

The key milestones below trace how each generation of standards addressed the limitations of the one before it.

2001 – CARB adopts Avcon connector

California’s adoption of the Avcon conductive plug ended the short-lived inductive paddle era and pushed automakers toward a shared conductive interface.

2008 – SAE J1772 (Type 1) gains consensus

Yazaki’s five-pin J1772 redesign boosted Level 2 AC charging to 19.2 kW, establishing a universal standard for nearly all non-Tesla cars in the U.S.

2010 – CHAdeMO launches in Japan

A new DC-only plug promised quick “tea-break” charges, sparking 400 kW ambitions and bi-directional power dreams.

2011 – CCS1 proposal merges AC/DC

To enable DC fast charging, automakers adopted a design that added two large DC pins to the existing J1772 AC connector, creating the Combined Charging System (CCS1) – a single inlet for both AC and DC power.

2012 – Tesla releases proprietary connector

Tesla developed a compact plug, about half the size of CCS, and a specialized version for its Semi truck is rated for over 1 megawatt (MW), but the technology remained exclusive to Tesla for a decade before being opened as a public standard.

2014 – ISO 15118-2 introduces Plug & Charge

Encrypted Power Line Communication lets cars handshake, authenticate, and start billing automatically, ditching swipe cards.

2022 – Tesla opens NACS (SAE J3400)

Tesla published designs and invited everyone to use its connector, touting twice the power and far more chargers.

2023 – Ford & GM announce NACS adoption

Detroit’s giants switched camps, citing Supercharger reliability and customer ease, triggering a rapid industry stampede.

2024 – Federal Highway Administration (FHWA) endorses NACS for National Electric Vehicle Infrastructure (NEVI) funding

Federal highway planners are updating grant rules to include the NACS plug, making billions in federal funding for interstate chargers accessible to this standard alongside the existing CCS requirement.

Early Interoperability: SAE J1772 Sets the Foundation

Among all early standards, one connector truly unified the fragmented charging landscape.

Before 2009, early EV owners carried multiple adapters because no two plugs were compatible. The Yazaki-designed SAE J1772 standard ended that chaos by combining Level 1 (1.4 kW) and Level 2 (up to 19.2 kW) charging in a single five-pin design.

Ground, control-pilot, and proximity pins allowed the car and station to communicate current limits and enable safe, automatic starts.

J1772 delivered higher power while preserving backward compatibility, allowing existing parking infrastructure to upgrade sockets without costly rewiring.

That design stability became the foundation for later combo standards such as CCS, which expanded J1772’s architecture to include DC fast-charging capability.

CHAdeMO vs CCS: Rival DC Fast Charging Frameworks

As automakers looked beyond Level 2 AC charging, two competing fast-charging systems emerged on opposite sides of the world.

• Japan’s CHAdeMO standard debuted first, offering 62.5 kW DC charging and later scaling toward 400 kW. It required a dedicated, bulky plug solely for DC power delivery.
• In contrast, CCS – backed by European and U.S. automakers – combined the existing AC interface with two additional high-current DC pins, enabling both slow and fast charging through a single inlet.

For U.S. hardware manufacturers, CCS simplified certification and reduced cable variations by keeping AC and DC integration within one connector family. Yet CHAdeMO’s early rollout left legacy fleets and infrastructure that still require support.

Even today, choosing which standard to include influences enclosure size, cooling architecture, and firmware complexity in Electric Vehicle Supply Equipment (EVSE) design.

Tesla’s NACS Adoption and the Industry Pivot

That regional competition soon gave way to a new contender – one built not by a consortium, but by a single company.

Tesla’s North American Charging Standard (NACS) redefined expectations for EV connectors. The design delivers both AC and DC power through the same slim contacts and anchors a dense Supercharger network, with the underlying technology capable of supporting up to 1 MW for commercial vehicles.

In 2023, Ford and GM partnered with Tesla to give their customers access to more than 12,000 Supercharger stalls – an extensive, reliable network that existing CCS infrastructure could not yet match in scale or uptime. Soon after, federal funding programs began favoring NACS-compatible sites, prompting hardware manufacturers to adapt quickly.

Today, most new roadmaps include dual-head configurations, relay switching, and firmware flexibility to support both CCS and NACS during the industry’s transition period.

ISO 15118: Secure Plug & Charge and Smart Energy Management

While connector standards unified the physical side of charging, communication protocols began redefining how vehicles, chargers, and the grid interact.

ISO 15118 – the global “vehicle-to-grid” language – sits at the center of this shift.

It allows the car, charger, and grid to communicate over the same power conductors using encrypted Power Line Communication (PLC).

Meanwhile, Version 20 strengthened security by making Transport Layer Security (TLS) and a public-key infrastructure (PKI) mandatory, eliminating the spoofing vulnerabilities found in earlier implementations.

In effect, two digital certificates exchange in milliseconds, allowing Plug & Charge to authenticate and begin billing automatically– no cards or apps required. The same secure channel can also coordinate off-peak charging schedules or send stored battery energy back to the grid during demand-response events.

For hardware teams, ISO 15118 means provisioning additional memory for digital certificates, integrating PLC couplers compatible with HomePlug Green PHY, and maintaining firmware update paths as utilities introduce new tariff and communication requirements.

Universal Charging Connectors and Compatibility Challenges

Even as communication standards mature, physical compatibility remains a separate engineering challenge.

Achieving a truly “universal” charging connector is more complex than it sounds, requiring harmony at both the pin and protocol levels. A NACS inlet saves space by delivering AC and DC power through the same slim contacts, but it still depends on software capable of speaking either Tesla’s original CAN bus or ISO 15118 as network transition.

CCS1 retains the familiar J1772 upper section with two added DC pins, while CCS2 replaces that AC half with Europe’s Type 2 geometry. The result: region-specific plugs that share identical message protocols but incompatible shapes. Adapters can bridge the physical gap, yet each adds resistance, new certification requirements, and field-failure risk.

Ultimately, true universality demands multi-port enclosures, intelligent routing relays, and firmware capable of handshaking with every protocol a roadside driver might present.

The Future of EV Charging Infrastructure and Standards

Beyond connector geometry, the next wave of innovation is reshaping how chargers deliver, secure, and manage power.

EV charging infrastructure is advancing toward higher currents, stricter cybersecurity, and new energy transfer methods. Tesla has already demonstrated its NACS connector operating above 900 amperes, proving that 1-megawatt charging is feasible using liquid-cooled cables with a standard, non-liquid-cooled vehicle inlet.

At the same time, ISO 15118-20’s mandatory TLS encryption signals that regulators increasingly view chargers as critical IT nodes. Regular software maintenance and patching will soon be as essential as hardware safety audits.

Meanwhile, wireless charging pads embedded in pilot roadways and curb-integrated systems are emerging, pointing toward more convenient and less cluttered urban charging environments.

Forward-looking engineering teams are already adapting to these shifts:

• Design for higher amperage: Oversize busbars and integrate liquid-cooled or hybrid cable options to prepare for megawatt-level charging.
• Enable protocol flexibility: Use modular communication boards that can be updated or swapped as standards evolve.
• Embed cybersecurity early: Conduct threat-model reviews and align firmware and network interfaces with IEC 62443 or equivalent frameworks.

Sustainability is now a parallel design priority:

• Energy efficiency: ENERGY STAR 1.2 caps standby draw at two watts, and many utilities tie rebates or incentives to that threshold.
• Interoperability testing: End-to-end Open Charge Point Protocol (OCPP) and ISO 15118 test benches can operate alongside safety-related current-control verification, ensuring consistent performance.
• Vehicle-to-Grid (V2G) readiness: Validation of bidirectional power transfer is moving from pilot to baseline expectation in fleet and utility programs.

Together, these trends mark a clear shift—from static compliance checklists to dynamic performance and sustainability benchmarks. Teams that anticipate these requirements today turn regulatory change from a scramble into a lasting market advantage.

‍

Conclusion

The history of EV charging standards reveals a clear pattern: every plug and protocol emerged to solve a tangible challenge – whether a physical mismatch, a fire hazard, or a cybersecurity gap.

Today’s innovators succeed not by reacting to the latest specification, but by anticipating where the next standards will lead. Treating evolving regulations as design guideposts transforms compliance from a hurdle into a trust badge – one that earns lasting confidence from both buyers and investors.

‍