Selecting EV Chargers: Part 1 – Maximum Charging Rate

Maximum Charging Rate — But in Context

Maximum Charging Rate is a reasonable starting point, but it needs context. Installation location, intended usage, available electrical supply and vehicle selection should all be considered before assuming that the highest kW figure is automatically the best option.

Domestic installations

For a domestic user, a 7.4kW single-phase charger is, in most cases, the practical upper limit and often the most balanced choice in the UK. A typical domestic property has a single-phase supply of somewhere between 60A and 100A, and a 7.4kW charger with suitable load curtailment can strike a good balance between charging speed, installation cost and DNO implications.

The important point is not simply whether the charger can deliver 7.4kW — it’s whether the property can support that output safely alongside the rest of the household load. Load curtailment limits the charging output so total site demand stays within the available supply capacity, which can make a 7.4kW charger suitable even where unrestricted output wouldn’t be appropriate.

A 3.7kW charger may be appropriate where the supply is very limited or the customer’s charging needs are modest. However, a configurable 7.4kW charger limited to a lower current usually offers better future flexibility than a fixed 3.7kW unit.

11kW and 22kW domestic charging is still relatively rare in the UK, though some newer properties, rural properties, larger homes, or privately developed properties may have three-phase supplies. Where that’s the case, it’s worth comparing 22 kW-capable chargers against 11 kW models rather than assuming 11kW is sufficient — the cost difference between the two is often reasonably low relative to the overall installation cost, and a 22 kW-capable charger provides more flexibility for the end user.

This is especially relevant where the household has, or may later have, a mix of battery electric vehicles (BEVs) and plug-in hybrids (PHEVs). Many vehicles are limited to 11kW AC charging, and some to 7.4kW or 3.7kW. Older plug-in hybrids were often limited to 3.7kW single-phase charging, but more modern plug-in hybrids increasingly support 7.4kW single-phase.

Private business sites

For a private business user where charging isn’t available to the general public — an office block, distribution centre, staff charging for an educational establishment, hotel or leisure venue, or similar site — the maximum charging rate should be weighed against actual usage needs. What’s the priority: higher charging rates, lower installation cost, or a greater number of charging outlets?

If staff vehicles are parked for most of the working day, 7.4kW chargers may be perfectly adequate, and more outlets at a lower charging rate may be more useful than fewer high-powered ones. If vehicles have shorter dwell times, or the site supports operational vehicles that need faster turnaround, then 11kW, 22kW or even DC charging may need to be considered.

Public commercial sites

For commercial charging at public sites (open to the general public), expected dwell time is a good starting point for analysis.

At locations like train stations or park & ride car parks, where vehicles are typically parked for 6-8 hours or more, a higher number of 7.4kW outlets may be the more optimal solution for maximising return on investment. At shopping or leisure centres, where drivers typically spend 2-4 hours, 11kW or 22kW stations may be the better fit. At locations with very short dwell times – supermarkets or service stations – DC charging is usually the most effective option.

Why 11 kW and 22 kW aren’t just about three-phase speed

An 11 kW three-phase charger is limited to around 16A per phase, which means some single-phase vehicles may only charge at around 3.7kW on it. A 22kW-capable three-phase charger, based on 32A per phase, may allow up to 7.4kW single-phase charging where the charger, vehicle and installation all support it. In other words, a 22kW charger isn’t only about faster three-phase charging — in some cases it also provides better flexibility for single-phase vehicles using the same unit.

In every domestic scenario, the right answer depends on a proper conversation about current and future needs — not just the lowest sticker price.

Beyond 22kW AC

Selecting AC chargers capable of delivering more than 22kW per outlet is, in most cases, a niche requirement. Few chargers on the market exceed this, and the number of vehicles that can make practical use of those rates is limited.

Unless the customer needs to charge a specific vehicle that supports high-power AC charging, going beyond 22kW AC can quickly become overly complicated and expensive. In many cases, a compact DC charger is the more practical route once requirements move beyond standard AC charging levels — DC brings its own cost, installation, maintenance and operational implications.

Designing for future three-phase upgrades

Where the limitation is available supply rather than cost, it’s worth exploring chargers that can operate on both single-phase and three-phase supplies — particularly where the customer is unsure of their future requirements. In these cases, the wiring and distribution design can be prepared with future three-phase charging in mind, while only a single phase is connected to the charger initially.

Should the customer upgrade their incoming supply later, this approach can significantly reduce the cost and disruption of moving to three-phase charging. It shouldn’t be treated as a negligible change, though — protective devices, distribution equipment, load management settings, testing, certification and DNO considerations may still need to be reviewed at that point.

The takeaway

Maximum Charging Rate should not be viewed in isolation. A higher kW figure does not automatically mean a better charger. The right choice depends on the supply, the vehicle, the dwell time, the number of users, the installation cost, the customer’s future plans and the wider electrical design — the same fields you’ll find in the EVCP Info comparison tool.

What to check