When you plug your electric car in at home using a standard three-pin socket, you’re charging in Mode 2. When you plug into a wallbox or a public AC charge point, you’re in Mode 3. The difference is about more than speed. It comes down to where the intelligence sits that keeps the charge safe. IEC 61851-1, the international standard that governs all EV conductive charging, defines four distinct modes. Understanding them takes about five minutes and will inform every cable decision you make.
What the IEC 61851-1 standard actually says
IEC 61851-1 is the international standard that defines four EV conductive charging modes. Each mode is a complete specification: it describes the type of socket or connection used, where the protective and communication devices live, and the maximum power that can be delivered. The modes are not marketing categories. They are engineering classifications with real legal and safety implications.
The standard exists because plugging a 400-volt battery system into a domestic electrical circuit without proper protection would be genuinely dangerous. Every mode in IEC 61851-1 is an answer to the question: “How do we make this safe?” The answers differ by context: home socket, dedicated charger, or rapid DC unit.
A quick word on Mode 1 (and why it’s banned in the UK)
Mode 1, charging from a standard domestic socket with no EV-specific protection or communication, is not permitted for EV use in the UK or EU. It is a legacy classification, predating modern EVs, that lacks the pilot signal and earth-fault protection now considered essential by IEC 61851-1. Some countries have banned it outright. If a cable has no moulded brick in the lead and plugs directly into a three-pin socket on one end and your car on the other, treat it with caution. It almost certainly does not comply.
Mode 2 charging: the granny charger you already own
Mode 2 is defined in IEC 61851-1 as charging from a standard socket, a 13 A three-pin plug in the UK or a 16 A Schuko in much of Europe, with an In-Cable Control and Protection Device (IC-CPD) built into the cable itself.
That brick-shaped unit moulded into the middle of your granny charger is the IC-CPD. It is not decorative. It is the device that makes Mode 2 legal and safe for EV use.
Where the safety intelligence lives in Mode 2
The defining characteristic of Mode 2 is that all safety and control intelligence is located in the cable, not in the wall socket or any fixed equipment. The IC-CPD (governed in detail by IEC 62752, the standard specifically written for these devices) performs three critical functions:
- Earth-fault protection: Monitors the earth connection and cuts power if it detects a fault.
- Current limiting: Restricts draw to 10 A on a UK 13 A plug, providing a safety margin below the socket’s rated capacity.
- Basic pilot signal: Sends a low-level communication to the car confirming the connection is live and safe.
Because all of this sits in the cable, no modifications to your domestic socket or consumer unit are required. You plug in; the IC-CPD does its work; the car charges.
Real-world speed: what 2.3 kW means overnight
The 10 A current limit set by the IC-CPD in a typical UK Mode 2 cable translates to roughly 2.3 kW of charging power. In practical terms, that is approximately 8 miles of range added per hour. For a car with a 60 kWh battery at 10% charge, a full charge from a Mode 2 cable takes roughly 24 hours.
That sounds slow, and compared to a wallbox, it is. But Mode 2 is never intended to be a primary charger. It is a backup, a travel cable, a solution for when you are visiting somewhere with no EV infrastructure. As a granny charger used overnight on a car that returns home with 40-80% charge remaining, 2.3 kW is usually sufficient.
Mode 3 charging: wallboxes, public posts, and proper speed
Mode 3 is charging via a dedicated EV charging point, either a home wallbox or a public AC post, where all safety intelligence is built into the fixed equipment (the EVSE), not the cable. This is the mode you use for everyday home charging if you have had a wallbox installed, and the mode behind every public AC charge point you encounter on a street, in a car park, or at a hotel.
The cable you need for an untethered Mode 3 wallbox, meaning one without a permanently attached lead, is a Type 2 to Type 2 cable (IEC 62196-2 both ends). Every new EV sold in the UK since approximately 2018 has a Type 2 AC inlet, so this cable fits your car and the wallbox socket.
How the pilot signal works
A key technical distinction between Mode 2 and Mode 3 is the pilot signal, and specifically how sophisticated it is in Mode 3. The EVSE sends a continuous 1 kHz PWM (pulse-width modulation) signal to the car via a dedicated pin on the Type 2 connector. The duty cycle of that signal encodes the maximum current the EVSE is willing to supply. The car reads the signal, confirms it is ready, and the EVSE releases power. This handshake runs throughout the charging session. If the connection is broken or the car signals a problem, the EVSE cuts power within milliseconds. Nothing equivalent to this level of ongoing communication exists in Mode 2.
Single-phase vs three-phase: the power arithmetic
Mode 3 operates across a wide power range depending on the EVSE’s supply and the car’s on-board charger capacity. Here is the arithmetic for the most common configurations:
- 16 A single-phase: 16 × 230 V ≈ 3.7 kW
- 32 A single-phase: 32 × 230 V ≈ 7.4 kW
- 32 A three-phase: 32 × 230 V × 3 ≈ 22 kW
Most UK domestic wallboxes are 7.4 kW (32 A single-phase). At 7.4 kW, that same 60 kWh battery charges from 10% in roughly 8 hours, comfortably overnight.
| Scenario | Power kW | Approx miles/hr |
|---|---|---|
| Mode 2: UK 13 A socket (10 A) | 2.3 | ~8 |
| Mode 3-16 A single-phase wallbox | 3.7 | ~13 |
| Mode 3-32 A single-phase wallbox | 7.4 | ~25 |
| Mode 3-32 A three-phase public AC | 22 | ~75 |
Mode 4 context: DC rapids (no cable to buy)
Mode 4 is DC rapid charging, delivered by an off-board charger, a Rapid or Ultra-Rapid unit using CCS, CHAdeMO, or similar DC protocols. It sits outside the Mode 2 vs Mode 3 conversation for one simple reason: the cable is permanently tethered at the charger unit itself. There is nothing to buy. You pull the tethered connector off its holster and plug it directly into your car’s DC inlet. Power ranges from 50 kW up to 350 kW at the fastest current installations.
Mode 4 units require significant electrical infrastructure and do not use the same AC supply chain as Modes 2 and 3. They are governed by IEC 61851-1 §6.4 but are a different product category entirely.
The full picture: Modes 1-4 side by side
No single page should make you hunt across multiple sources for this. Here is every mode defined by IEC 61851-1, in one place:
- Headers: [Attribute, Mode 1, Mode 2, Mode 3, Mode 4]
- Rows:
- [Standard ref, IEC 61851-1 §6.1, IEC 61851-1 §6.2 + IEC 62752, IEC 61851-1 §6.3, IEC 61851-1 §6.4]
- [Socket / connection, Standard domestic socket, Standard domestic socket (13 A UK / 16 A EU), Dedicated EVSE (wallbox / public AC post), DC off-board EVSE (rapid charger)]
- [Control location, None, In-cable IC-CPD, Fixed EVSE equipment, Fixed EVSE equipment]
- [Typical power, Up to 16 A AC, ~2.3 kW (10 A, UK), 3.7 kW, 22 kW AC, 50 kW, 350 kW DC]
- [UK permitted?, No, Yes, Yes, Yes]
- [Cable to buy?, N/A (not permitted), Yes, granny cable with IC-CPD, Yes, if wallbox is untethered (Type 2 to Type 2), No, tethered at charger]
Which mode do you actually need?
The honest answer is: most EV drivers in the UK need both Mode 2 and Mode 3 capability at different points in their ownership.
A Mode 2 granny cable belongs in the boot of every EV as a backup. You may never need it. Or you may need it the day your wallbox develops a fault, the night you stay somewhere with only a domestic socket, or the weekend you visit family who have not yet installed a charge point. It is not your primary charger; it is your insurance.
A Mode 3 cable, a Type 2 to Type 2 lead, is what you use every day if your wallbox is untethered, and what you carry to access untethered public AC charge points. It is the cable that delivers real charging speed: 7.4 kW overnight at home, or 22 kW at a capable three-phase public post.
For a fuller breakdown of which specific cable matches your car, your wallbox, and your typical use case, our guide to which cable you need walks through every scenario.
Frequently asked questions
What is Mode 2 EV charging?
Mode 2 charging uses a standard domestic socket, a 13 A three-pin plug in the UK, combined with a cable that contains a built-in safety device called an IC-CPD (In-Cable Control and Protection Device), governed by IEC 62752. The IC-CPD provides earth-fault protection, current limiting to 10 A, and basic communication with the car. Mode 2 is what most people call a granny charger, delivering roughly 2.3 kW.
What is Mode 3 EV charging?
Mode 3 charging uses a dedicated EV charging point, either a home wallbox or a public AC post, where all safety intelligence and the pilot signal are built into the fixed equipment, not the cable. For untethered wallboxes, the cable is a Type 2 to Type 2 lead (IEC 62196-2). Mode 3 typically delivers 3.7 kW (16 A) to 22 kW (32 A three-phase) depending on the EVSE and car.
How fast is Mode 2 vs Mode 3 charging?
A UK Mode 2 cable is limited to 10 A by its IC-CPD, delivering roughly 2.3 kW (around 8 miles of range per hour). Mode 3 begins at 3.7 kW (16 A single-phase) and scales to 7.4 kW (32 A single-phase) at most domestic wallboxes, or 22 kW (32 A three-phase) at capable public AC charge points.
Is Mode 1 EV charging legal in the UK?
No. Mode 1, charging from a standard socket with no EV-specific protection or pilot signal, is not permitted for EV use in the UK or EU. IEC 61851-1 includes it as a classification but the UK and EU regulatory framework prohibits its use for EVs. Mode 2 (with an IC-CPD) is the minimum standard for domestic socket EV charging.
Do I need to buy a cable for Mode 4 rapid charging?
No. Mode 4 DC rapid chargers (CCS, CHAdeMO) have a permanently tethered cable at the unit. You connect the tethered plug to your car’s DC inlet. No cable purchase is needed or possible.
What is an IC-CPD and why does it matter?
An IC-CPD (In-Cable Control and Protection Device) is the safety unit built into every Mode 2 granny cable, specified by IEC 62752. It provides earth-fault protection, current limiting, temperature monitoring, and a basic pilot signal to the car. It is the sole reason a Mode 2 cable can be used safely with an ordinary domestic socket.
What connector does a Mode 3 cable use in the UK?
For AC charging in the UK, the standard connector is Type 2 (IEC 62196-2) on both ends of the cable: one end into your car’s AC inlet, the other into an untethered wallbox or public AC post socket. Every new EV sold in the UK since around 2018 uses a Type 2 AC inlet.
What is the pilot signal in Mode 3 charging?
The pilot signal in Mode 3 is a continuous 1 kHz PWM signal sent between the EVSE and the car via a dedicated pin on the Type 2 connector. The duty cycle encodes the maximum current available. The car reads it, signals readiness, and the EVSE releases power. This ongoing handshake, absent in Mode 2, is what allows Mode 3 to operate at higher currents safely.