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EVSE How EV Charging Works

EVSE stands for Electric Vehicle Supply Equipment (the wallbox / charge point). People often call it “the charger”, but on AC charging the actual battery charger is inside the car itself. The EVSE is the safety controller that decides when the connector can be energised and how much current is allowed. So the thing on the wall at home with the Type 2 socket, the lights, the beeps and the app, is actually an EVSE wallbox (a charge point), not a battery charger. “Charge point” is often the simplest and most accurate name for it.

This EV charging guide is written in plain English, but it’s detailed enough to answer the questions curious people always ask (and the questions that stop unsafe myths spreading). So, how does it all work?

Quick summary

  • Type 2 EV connectors are permission-based: the power pins are isolated by an open contactor until permission is granted.
  • CP (Control Pilot) is the permission wire and live “current governor” that tells the vehicle what it may draw.
  • PP (Proximity Pilot) is detachable cable identity / cable rating coding used mainly with Mode 3 leads.
  • Mode 2 (granny charger) has the EVSE brain in the inline box; Mode 3 has the EVSE brain in the wallbox/post.
  • Daisy-chaining EV charge leads is not allowed: it can break the intended safety/identity logic and may breach manufacturer instructions and public network terms.

Contents

What an EVSE actually does

An EVSE is not just a live power socket. It’s best understood as a safety gate between the power supply and the vehicle inlet. Its job is to keep the connector electrically isolated until the correct conditions exist.

  • Keeps the power pins isolated by default: the internal contactor is open (physically disconnected) until permission is proven.
  • Performs a handshake: it verifies a valid “vehicle present / ready” state before energising.
  • Publishes a current limit: it tells the vehicle (continuously) what maximum current is allowed.
  • Drops power fast on faults: if the handshake becomes invalid, the EVSE opens the contactor and removes supply.

Why Mode 1 does not work on modern EVs

“Mode 1” is often described (incorrectly) as “just feed mains into the car”. In practice, modern Type 2 AC charging is deliberately designed to refuse to accept power unless a valid Control Pilot (CP) handshake is present.

People sometimes imagine a “Mode 1” setup as a simple mains fly-lead that goes from a live socket to a CEE or Type 2 inlet on the car. But without a valid CP state, a modern vehicle will not close its internal charging relays, so no charging starts.

This prevents unsafe “live inlet” scenarios and is why so-called “Mode 1” connections are deprecated and non-functional on modern EVs. (If you have an older EV that does use Mode 1 and you want to be able to connect to an EVSE then check out our Type 2 socket converter solutions.)

Control Pilot (CP): permission + live current governor

CP is the permission wire. It’s the line that makes EV charging different to an ordinary socket. Without a valid CP handshake, the EVSE will not close its contactor, so the connector remains isolated (switched off).

CP as “permission to energise”

The EVSE generates a pilot signal on CP and watches how the vehicle (or a CP-simulating device) loads that line. When the EVSE sees the expected “vehicle present” and “ready” states, it closes the contactor, switches on the power and energises the connector. If CP becomes invalid at any point, the EVSE opens the contactor and turns off the power again.

CP as a live “current governor” (the speed-limit sign)

CP is not a one-time handshake. CP is a live current limit broadcast. The EVSE continuously advertises the maximum current it is willing to supply.

The key idea:

  • CP can change while power is flowing.
  • A correctly behaving vehicle (or CP-simulating device) must reduce its draw in real time if the EVSE reduces the limit. In app terms, users often see this as “7.4 kW now 6.6 kW”. Electrically, that’s the EVSE lowering the advertised current limit (for example, roughly 32 A down to roughly 28–29 A on single-phase).

Why “simulated CP” can work in one setup and fail in another

In the real world, EVSE units often validate more than “a waveform exists”. They may check expected electrical behaviour (including diode/resistor signatures and state transitions). This is why some CP-simulating devices work perfectly when plugged directly into an EVSE socket, yet fail when placed at the end of certain leads/tethers: you can end up violating the EVSE’s expected state machine or electrical checks.

For solutions built specifically around these real-world behaviours, see our use on the end of a cable option, or direct plug-in to an EVSE socket option.

Proximity Pilot (PP): cable identity and why “two PP codes” can interfere

PP is the detachable-cable identity line. In plain terms, PP is used to tell the system what current a detachable charging lead is designed to carry.

What PP solves

On Mode 3 setups with detachable leads, the charge point needs a way to avoid offering a current that a smaller cable cannot handle. PP provides that “cable rating identity” so the system can behave sensibly.

Real-world behaviour: multiple PP resistors can electrically interfere

In simplified diagrams, people imagine PP as a neat, single identity. In the real world, if you introduce additional PP coding downstream (for example by stacking devices/leads that each present a PP resistor), the EVSE may measure an effective PP value that no longer matches an expected “valid cable rating band”.

What happens next depends on the EVSE’s firmware:

  • Some EVSE units refuse to energise because the PP value looks “unknown / invalid”.
  • Others may energise but behave unpredictably because the topology is not the one they were designed to supervise.

This is one of the reasons “daisy-chain” and “stacking” behaviour is not supported: you can accidentally create a PP signature that fails sanity checks or defeats the intended identity logic.

Mode 2 vs Mode 3: why topology matters

These two modes are often mixed up. The difference is simple:

Mode 2 (granny charger / IC-CPD)

  • The EVSE brain is in the inline control box on the cable.
  • The EVSE typically advertises a lower, fixed current (often 8–10 A).
  • The “vehicle permission” is still CP-based, but the overall topology is different to Mode 3.

For related products and guidance, see: Mode 2 / granny charger options.

Mode 3 (wallbox / public AC post)

  • The EVSE brain is in the charge point (wallbox / post).
  • Detachable leads are part of the system design, including the cable identity behaviour (PP).
  • Public units may also do site-wide power management and backend control.

Mode 4 (DC Fast Charging) 

DC Charging will ve covered in a seperate page link to go here

Copper-safe vs protocol-safe vs standards-safe

This one concept clears up a lot of confusion:

  • Copper-safe: the conductors can carry the current without overheating (for example, 2.5 mm² for 16 A, or 6 mm² for 32 A, depending on install conditions).
  • Protocol-safe: CP/PP signalling behaves as intended, and the EVSE can correctly supervise the topology.
  • Standards-safe: the configuration matches manufacturer instructions and the intended charging mode definitions.

Something can be copper-safe yet still be protocol-unsafe or not standards-safe. That’s why “it seems to work” is not the same thing as “it’s a correct topology”.

Why EV charge leads must not be daisy-chained

People ask this because EV charge leads look like extension leads. They are not. EV charging is permission-based and identity-coded.

Daisy-chaining can cause two classes of problems:

1) It may refuse to start

Some EVSE units will reject the chain because CP/PP behaviour no longer matches a valid expected configuration. This often shows up as “fault / refuse to energise”.

2) It may start, but still be wrong

Some combinations can appear to “work”, but the topology can defeat the intended supervision logic, or create PP identity interference. This is the dangerous category because nothing obviously fails, yet the system is no longer operating in the intended, supervised configuration.

Bottom line: Do not daisy-chain EV charge leads. It can breach manufacturer instructions, site rules, and public network terms, and it can create signalling/identity states the EVSE was never designed to supervise.

If you have a tethered EVSE wallbox (built-in cable) and it’s not long enough to reach, the solution is not to add an extra charge cable on the end as an extension. The ideal solution is to replace the whole tether with a correctly specified replacement: EVSE tether replacement cable.

Load-balancing: why public chargers behave differently to home chargers

Many domestic installations are stable: one EVSE, one supply limit, predictable behaviour. Public charge points are often dynamic: multiple users, site demand limits, backend controls, and active load management.

Remember: CP is a live governor. On load-balanced systems, the EVSE can reduce the current limit at any time. Any device behaving as the “vehicle” in that handshake must track CP continuously and respond to changes.

This is why higher-current operation can be more problematic on dynamic public networks than on a controlled private installation: you’re closer to ceilings, and CP limit changes can be more frequent.

EVSE-to-mains devices: “auxiliary power”, not certified EV charging equipment

Some products use the EVSE interface to provide auxiliary mains power in controlled scenarios. It’s important to describe these devices correctly:

  • They are auxiliary power devices, not “EV charging equipment”.
  • Use on public charging networks is always subject to the network operator’s terms and conditions.
  • Public network environments are often load-managed, so behaviour can be different to a simple home installation.

Practical guidance many users find helpful:

  • Lower current operation typically sits inside normal public AC load envelopes. 16A
  • Higher current operation can be more sensitive to dynamic load-balancing behaviour and site limits. 32A

FAQ

Can a Type 2 EV charging socket switch on without Control Pilot (CP) permission?

In normal operation, no. The EVSE keeps the connector isolated by an open contactor (switched off) until a valid CP state is present.

Is Control Pilot (CP) a handshake only, or a live limit while the EV is charging?

CP is active continuously. It acts like a live “speed limit sign” and the allowed current can change in real time.

What does Proximity Pilot (PP) do on a detachable Mode 3 Type 2 charging lead?

PP is used as cable identity/cable rating coding so the system can respect the current capability of a detachable lead.

Why can PP values become “unknown” when you stack leads or devices in a chain?

Stacking devices/leads can create an effective PP value that falls outside expected bands, triggering firmware sanity checks.

Why is daisy-chaining Type 2 EV charging leads unsafe even if the copper looks “thick”?

Because EV charging relies on CP/PP topology and supervision. Something can be copper-safe yet protocol-unsafe or not standards-safe.

Why do public AC charge points behave differently from home wallboxes on load-balanced sites?

Public networks often adjust CP limits dynamically to manage site demand, so the allowed current can change frequently.

What happens if the EVSE lowers the CP limit but the load keeps pulling more power?

A compliant load reduces current. If it doesn’t, the EVSE may open its contactor and stop supply, then report a fault.

What’s the simplest difference between Mode 2 granny chargers and Mode 3 wallboxes/posts?

Mode 2 has the EVSE brain in the inline box; Mode 3 has the EVSE brain in the charge point itself.

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