Interoperability means several things: the charger talking to its operator, operators sharing data, and the vehicle authenticating with the charger.
OCPP is station-to-backoffice
The Open Charge Point Protocol is an open communication specification between charging equipment and a management system. OCPP implementations can manage transactions, diagnostics and smart charging; the Open Charge Alliance records 1.6, 2.0.1 and 2.1 as distinct released versions with different capabilities. OCPP support is not evidence that every driver can pay at a different network or that every vehicle connector will fit.
OCPI handles ecosystem data and roaming
Open Charge Point Interface is used to exchange network information such as station locations, availability and roaming-related data. The UK's public charge point regulations use OCPI for specified open-data obligations. A site can display an OCPI station listing yet still have a broken physical connector, a stale status signal or restrictions on user access.
Plug & Charge is vehicle-to-EVSE authorization
ISO 15118 provides vehicle-to-charger communication. Plug & Charge implementations can authenticate a vehicle using digital certificates and a compatible commercial arrangement, reducing dependence on app or card interaction. ISO 15118-20 addresses communication for second-generation and bidirectional power transfer, but a published standard does not by itself make a particular car and charger interoperable.
Separate the checks
For reliable editorial information, report connector fit, supported power, site availability, authentication and payment separately. A station can be accessible with a card yet lack Plug & Charge; another can support Plug & Charge only with certain brands. Real-world access requires both protocol capability and an active operator agreement.
A session crossing several software boundaries
A charging operator's station can report status to its management service using OCPP. That operator may share location and roaming-related information with a third-party platform using OCPI. Meanwhile, a compatible electric vehicle and charger can negotiate power and, where configured, exchange contract-certificate information for Plug & Charge through ISO 15118. These messages serve different audiences and functions. An OCPI map showing a stall as available does not validate the vehicle's ISO 15118 handshake; an OCPP-compliant charger does not automatically make roaming payment legal or available in every country.
Failure-mode isolation
If a card works but automatic Plug & Charge fails, investigate contract provisioning and vehicle/station support instead of assuming the power connector is defective. If several apps show outdated station status, examine the operator's data flow and synchronization before blaming the vehicle. If a charger loses back-office connectivity, some systems may continue local authorization and others may not. OCPP version labels should not be used as substitutes for interoperability testing across vehicle, hardware and roaming service providers.
Focused Reader Questions
Does OCPP certify connector compatibility?
No. OCPP governs communication between equipment and operator management, not the physical plug or battery electrical limits.
Does OCPI show guaranteed live occupancy?
No. Data timeliness and correctness depend on the operator’s reporting system; displayed states can lag reality.
Is ISO 15118 automatic payment for every EV?
No. Plug & Charge requires compatible implementation, valid contract credentials and commercial/network support.
Can a charger support more than one protocol layer?
Yes. An installation may use OCPP to its operator, OCPI for roaming and ISO 15118 with compatible cars.
Sources and Further Reading
Scope: 2020–2026 vehicles and the regions identified above. Charging access, legal obligations, warranties and vehicle equipment must be checked for the particular market, model year and date.