Pick up any EV charging cable and you’ll see a number stamped near the plug: 10A, 16A, 32A. That figure tells you the maximum current the cable can safely carry, but on its own it tells you nothing about how fast your car will actually charge. The amps rating, the voltage of your supply, the number of phases in your circuit, and the capacity of your car’s onboard charger all have to align before you can calculate a real charging speed. We’ll walk you through exactly how that works.
What does the amp rating on an EV cable actually mean?
The amp rating of 10A, 16A or 32A is the maximum current the cable can safely carry continuously. It sets a ceiling on how much power can flow, but it does not determine your actual charge speed by itself. Your voltage, number of phases and car’s onboard charger all factor in.
Think of it like a pipe diameter. A wider pipe can carry more water, but only if the pressure and pump on either end can push it through. In EV charging, the cable is the pipe. The grid supply provides the pressure. And the car’s onboard charger is the pump: it decides how much current actually flows.
Amps as a ceiling, not a speed
A 32A cable used on a 7.4kW wallbox does not guarantee 7.4kW of charging. It guarantees the cable can handle 32A without overheating. If your car only accepts 16A of AC input, the cable will carry 16A. It simply will not be the limiting factor. Oversizing is safe. Undersizing is not: a 16A cable on a 32A circuit risks overheating at the connector and along the conductor, which is why cable amperage must be taken seriously when sizing for a new installation.
How to calculate charging power from amps (the formula)
There are two versions of the power formula, depending on whether your circuit is single-phase or three-phase.
Single-phase: P = V × I / 1,000
For a standard UK single-phase supply at 230V:
P (kW) = 230 × Amps ÷ 1,000
A 32A single-phase circuit therefore delivers: 230 × 32 ÷ 1,000 = 7.36kW (conventionally called 7.4kW).
Three-phase: P = √3 × V × I / 1,000
Three-phase supplies introduce a factor of √3 (approximately 1.732) because power is delivered across three staggered waveforms simultaneously:
P (kW) = 1.732 × 230 × Amps ÷ 1,000
A 32A three-phase circuit therefore delivers: 1.732 × 230 × 32 ÷ 1,000 = 12.75kW per phase × √3 correction = 22.08kW, conventionally called 22kW.
Note: the 400V figure you will sometimes see for three-phase is the line-to-line voltage (230V × √3 ≈ 400V). Both routes give the same answer.
- Formula 1: Single-phase. P (kW) = 230V × Amps ÷ 1,000
- Formula 2: Three-phase. P (kW) = 1.732 × 230V × Amps ÷ 1,000
- Row 1: 10A | Single-phase | 230V | 2.3kW | Granny / Mode 2 (13A plug)
- Row 2: 16A | Single-phase | 230V | 3.7kW | Commando blue / slower EVSE
- Row 3: 32A | Single-phase | 230V | 7.4kW | Standard home wallbox (most UK installs)
- Row 4: 16A | Three-phase | 400V | 11.1kW | Public AC (some cars cap here)
- Row 5: 32A | Three-phase | 400V | 22.2kW | Three-phase wallbox / public AC post
The 10A, 16A and 32A table: what power does each deliver?
| Current | Phase | Voltage | Power | Typical use |
|---|---|---|---|---|
| 10A | Single-phase | 230V | 2.3kW | Granny / Mode 2 (13A plug) |
| 16A | Single-phase | 230V | 3.7kW | Commando blue / slower EVSE |
| 32A | Single-phase | 230V | 7.4kW | Standard home wallbox (most UK installs) |
| 16A | Three-phase | 400V | 11.1kW | Public AC (some cars cap here) |
| 32A | Three-phase | 400V | 22.2kW | Three-phase wallbox / public AC post |
For a closer look at how 16A and 32A cables compare in practice, including which to choose if you’re unsure, see our 16A vs 32A cable guide.
The 2.3kW figure for 10A granny cables is worth pausing on. A standard UK 13A domestic socket only safely supports a continuous load of around 10A (approximately 8 miles of range per hour). Granny (Mode 2) cables are governed by IEC 62752, which explicitly limits their maximum output when connected via a domestic plug. If you see a marketplace listing claiming a granny cable can deliver a continuous 13A through a household socket, treat that as a safety red flag. The standard does not permit it.
Why your car might charge slower than the cable allows
This is the most commonly misunderstood part of EV charging specs, and it matters more than almost anything else when choosing a cable.
The onboard charger is the real ceiling
The onboard charger (OBC) is a component built into the car that converts AC grid electricity into the DC power that charges the battery. Its rated capacity, expressed in kilowatts, sets the absolute maximum AC input the vehicle will accept. No cable, no wallbox, and no grid supply can push more power through than the OBC will accept.
For a full picture of how fast your EV will charge based on your specific car and circuit, our dedicated guide runs through the calculations in detail. Here, the key point is that the cable’s amp rating is a ceiling, not a commanded speed, and the OBC is the ceiling that actually matters.
- Box 1: Grid circuit / MCB, ceiling 32A
- Box 2: Type 2 cable, ceiling 32A
- Box 3A: OBC, Nissan Leaf 30kWh, 6.6kW ≈ 29A actually drawn (amber)
- Box 3B: OBC, Standard 7.4kW EV, 7.4kW ≈ 32A actually drawn (green)
- Box 3C: OBC, PHEV 3.7kW, 3.7kW ≈ 16A actually drawn (amber)
- Footer label: Actual charge rate = the lowest ceiling in the chain
Real-world examples by car model
To make this concrete, consider three scenarios all using a 32A Type 2 cable on a standard 7.4kW home wallbox:
Nissan Leaf (30kWh, 6.6kW OBC): The OBC accepts 6.6kW maximum, which means it draws approximately 28.7A. The 32A cable is correctly rated and carrying current safely below its limit, but the car never reaches 32A. Charge speed is set by the OBC, not the cable.
Renault Zoe (later variants, 22kW OBC): This car has a three-phase onboard charger capable of 22kW. On a single-phase 32A home wallbox, it will only draw single-phase current and top out at 7.4kW. Three-phase infrastructure (and a 32A three-phase Type 2 cable) is needed to reach its full potential. See our 7kW vs 22kW charging guide for more on when upgrading to three-phase makes sense.
Typical PHEV (3.3-3.7kW OBC): Many plug-in hybrids have modest onboard chargers rated at 3.3kW or 3.7kW, drawing only around 14-16A. A 16A cable is technically sufficient for the car, but if the wallbox circuit is 32A, the cable must still be rated 32A, because the cable rating must match the circuit, not the car’s draw. More on that below.
How cable amps connect to your fuse or MCB
BS 7671:2018+A2:2022 (IET Wiring Regulations), Section 722 is the UK national standard for EV charging installations, and it requires the rated current of the cable to be at least equal to the rating of the circuit’s protective device. That protective device is typically a miniature circuit breaker (MCB) or a fuse.
For a standard 32A EV charging circuit, the installation would typically include a 40A MCB (sized above the design current to avoid nuisance tripping) with a Type B RCD providing the 6mA DC fault detection required under Section 722. The Type 2 cable used on that circuit must be rated for at least 32A, because the MCB will allow up to 32A of sustained current before it trips, and a 16A cable in that position would be at genuine risk of overheating.
This is the core safety principle: a cable’s amp rating must never be below the circuit’s protective device rating. Oversizing the cable (e.g. using a 32A cable on a 16A circuit) is fine, since the MCB limits current to 16A regardless. Undersizing is a hazard.
IEC 62196-2, the international standard governing Type 1 and Type 2 EV connector and inlet specifications, also sets the rated currents that connector contacts must sustain without excessive temperature rise. A cable stamped 32A has been designed and tested to carry that current continuously within the parameters the standard defines, which is why you should not mix cable amp ratings with circuit ratings carelessly.
Which amp rating do you need?
For most UK drivers, the answer is a 32A Type 2 cable.
Standard domestic EV charging installations are built around 7kW (32A single-phase) wallboxes, the most common setup approved under the UK’s EV charging grant schemes. A 32A cable matches the circuit, gives the onboard charger full headroom regardless of model, and future-proofs you if you upgrade your car to one with a higher-capacity OBC.
A 16A cable is appropriate only if your dedicated EV circuit is specifically designed for 16A and your electrician has confirmed the MCB rating. Some older or budget EVSE units operate on 16A circuits, and if you are charging a PHEV that will never draw more than 3.7kW, a 16A setup is electrically valid, provided the cable rating matches the circuit.
For drivers considering three-phase installations to reach 22kW charging, a 32A three-phase Type 2 cable is required. This is a different product from a single-phase 32A cable even though both carry the same per-phase current. Confirm phase compatibility before purchasing.
Frequently asked questions
What does 32A mean on an EV cable?
It means the cable can safely carry a maximum of 32 amperes continuously. On a standard UK single-phase 230V supply, that translates to approximately 7.4kW of charging power. On a three-phase 400V supply it supports up to 22kW. The figure is the cable’s current ceiling, not a guarantee of charging speed, which depends on your car’s onboard charger.
Is a 32A cable always faster than a 16A cable?
The cable itself only sets the ceiling. If your car’s onboard charger is rated at 3.7kW, it will draw roughly 16A regardless of whether the cable is rated 16A or 32A. Using a 32A cable in that situation is not faster, but it is correct practice if the circuit is 32A, because the cable’s amp rating must match or exceed the circuit’s protective device rating.
Can I use a 32A cable on a 16A circuit?
Yes. The cable is oversized for the circuit, which is perfectly fine. The circuit’s MCB or fuse will limit current to 16A. The risk only runs the other way: a 16A cable on a 32A circuit is undersized and can overheat under sustained load.
What amp cable do I need for a 7kW home wallbox?
A 32A Type 2 cable. Standard 7kW wallboxes operate on a 32A single-phase circuit, delivering up to 7.36kW. Your cable must be rated at 32A to match the circuit’s protective device, even if your particular car draws less than 32A.
Why is my granny charger limited to 10A and not 13A?
Granny (Mode 2) cables are governed by IEC 62752, which limits their maximum output to 10A (approximately 2.3kW) when connected via a standard UK 13A domestic plug. The plug fuse protects the socket, but sustained loads above 10A are not considered safe for long-duration EV charging on a standard ring main. Any marketplace listing claiming a continuous 13A output from a domestic-plug granny charger should be treated as a safety concern.
Do I need a special cable for three-phase charging?
You need a Type 2 cable rated for three-phase, and most 32A Type 2 cables support three-phase by design under IEC 62196-2. However, your car also needs a three-phase onboard charger to use the full 22kW. Cars with single-phase onboard chargers will still draw only single-phase current even when connected to a three-phase supply, so the cable phase rating only becomes relevant when both the supply and the vehicle support three-phase operation.
What is an onboard charger and how does it affect cable amps?
The onboard charger (OBC) is a component inside the car that converts AC mains power into DC power for the battery. Its rated capacity, expressed in kilowatts, determines the maximum AC current the vehicle will request from the cable and wallbox. A cable must be able to carry that current, but the car will never draw more than the OBC permits. The OBC is the ceiling that determines real-world charge speed; the cable’s amp rating is the ceiling that must not be exceeded for safety reasons.