IEC 61851 is an international standard series for electric vehicle conductive charging systems. It defines the core safety, functional, and operational requirements for EV charging equipment (EVSE) and how it interacts with an electric vehicle during charging—covering concepts such as charging modes, control-pilot signaling, protection functions, and requirements for both AC and DC charging equipment.
What Is IEC 61851?
IEC 61851 provides a technical framework for designing and deploying EV charging systems, including:
– Safety requirements for EV supply equipment and charging interfaces
– Functional behavior of charging modes (Mode 1–4)
– The control and signaling used to enable/disable charging and limit current
– Requirements that support interoperability between EVs and chargers
It is one of the core standards families underpinning modern EV charging infrastructure.
Why IEC 61851 Matters in EV Charging
IEC 61851 is foundational because it helps ensure:
– Electrical safety for users and installers (fault protection, safe energization)
– Compatibility between vehicles and charging stations across markets
– Predictable charging behavior in public, commercial, and fleet deployments
– A consistent basis for commissioning and compliance verification
For OEMs and CPOs, IEC 61851-aligned design supports scalable deployment and reduces interoperability issues.
IEC 61851 Charging Modes
IEC 61851-1 defines four charging modes commonly used to classify charging setups:
– Mode 1 – Charging from a standard socket outlet without dedicated control and protection (restricted or not allowed in many countries)
– Mode 2 – Charging from a socket outlet using an in-cable control and protection device (IC-CPD)
– Mode 3 – Charging from dedicated AC EVSE with control and protection functions (common for public and commercial AC charging)
– Mode 4 – DC charging with off-board power conversion (DC fast charging)
Control Pilot and Charging Control Logic
For AC conductive charging (commonly Mode 3), IEC 61851-1 defines the use of Control Pilot (CP) signaling to manage safe charging:
– The charger and vehicle use CP states to confirm connection and readiness
– The charger communicates the available current limit using PWM duty cycle
– Charging is enabled only when safety conditions are satisfied
This CP/PWM approach is closely aligned with how many AC charging systems manage interoperability in the field.
Key Parts of the IEC 61851 Standard Series
IEC 61851 is split into multiple parts that cover different aspects of charging systems, including:
– IEC 61851-1 – General requirements (applies up to 1,000 V AC or 1,500 V DC in the 2017 edition)
– IEC 61851-21-1 / 21-2 – EMC requirements (vehicle-side and off-board charging equipment)
– IEC 61851-23 – DC EV supply equipment (DC charging station requirements)
– IEC 61851-24 – Digital communication for control of DC charging
How IEC 61851 Relates to Other EV Charging Standards
IEC 61851 is often used alongside:
– IEC 62196 (connector and coupler types such as Type 2)
– ISO 15118 (higher-level digital communication, including Plug & Charge)
– OCPP (charger-to-backend communication for monitoring and control)
IEC 61851 primarily focuses on the charging system’s conductive operation and safety/control behavior, while these other standards address connectors, vehicle digital communication, and backend interoperability.
Related Glossary Terms
AC Charging
DC Charging
Mode 3 Charging
Mode 4 Charging
Control Pilot (CP)
PWM Signaling
IEC 62196
ISO 15118
Plug & Charge
OCPP