What happens when I tap my charging card?

The charger asks its operator's backend whether the card may charge. For another company's card, the backend checks it with the roaming partner or with a list of cards it received in advance.

Explained in

EV charging fundamentals · Stop 03What happens after you tap your card?Follow one tap from the card reader to the operator's backend and, for another company's card, across the roaming route and back. OCPP and OCPI in action.
  • OCPP connects the charger with its own operator's backend: status, meter values, authorisations, start and stop.
  • OCPI connects companies: operators and card providers exchange card lists, tariffs, locations and session records.
From “Two protocols with two jobs”, stop 03

Terms

  1. OCPPOpen Charge Point Protocol: the open protocol between a charger and its operator's backend.
  2. OCPIOpen Charge Point Interface: an open protocol for roaming between operators and e-mobility service providers.
  3. RoamingCharging in another company's network with your own card or app.
  1. What is the difference between OCPP and OCPI?OCPP connects a charger with its own operator's backend. OCPI connects companies, so operators and card providers can exchange card lists, tariffs and session records.
  2. How can my card work at another company's charger?Through roaming: operators and card providers exchange card lists, prices and session records, directly or through a roaming hub, and settle in the background.
  3. Why does charging involve so many companies?Three things spread the work: the grid connection, the location where people park, and contracts that work across many networks. One company can hold several roles, but the roles stay separate.
  4. Who is the CPO and who is the eMSP?The CPO operates the charger and keeps it available. The eMSP issues the card or app, sets the driver's price and sends the invoice. One company can hold both roles.
  1. Open Charge Alliance: Open Charge Point Protocol (OCPP). https://openchargealliance.org/protocols/open-charge-point-protocol/. Checked 07 Oct 2026.
  2. EVRoaming Foundation: Open Charge Point Interface (OCPI). https://evroaming.org/ocpi-background/. Checked 07 Oct 2026.