What Size Cable for EV Charger

As more drivers across the UK switch to electric vehicles, one of the most common questions asked during the installation of a home charger is what size cable is required. Choosing the right cable size is not just about efficiency, it is also a matter of safety and compliance with UK electrical regulations. An undersized cable can lead to overheating, voltage drop, or even fire risks, while an oversized cable can make installation unnecessarily expensive. Understanding how cable size is determined and what is recommended for EV chargers can help homeowners make informed decisions when planning an installation.

The Importance of Cable Sizing

The cable that connects your EV charger to your consumer unit must be correctly rated to handle the electrical load. In the UK, EV chargers typically operate on either a 7kW single phase supply or a 22kW three phase supply. Each requires a different cable size to ensure safe operation. If the cable is too small, it will not be able to carry the current demanded by the charger, leading to excessive heat build-up. If the cable is too large, it may be difficult to route and will increase costs unnecessarily. For this reason, the correct balance must be achieved by following the wiring regulations and applying professional calculation methods.

Factors That Affect Cable Size

There is no one size fits all answer to the question of EV charger cable sizing. Several factors influence the decision. The most obvious is the charging capacity, whether it is a 7kW or 22kW unit. The length of the cable run also plays a key role, as longer runs increase the risk of voltage drop. Installation method is another consideration, as cables buried in walls or ducts may need to be larger than those clipped directly to a surface due to heat dissipation. Ambient temperature, grouping with other cables, and the material of the conductor, usually copper, are also taken into account by the installer.

UK electricians work to the IET Wiring Regulations (BS7671), which provide detailed guidance on cable sizing. The calculations involve assessing current demand, applying correction factors for installation conditions, and ensuring voltage drop remains within permitted limits. While the regulations allow some flexibility, they make clear that safety must always take priority.

Typical Cable Sizes for EV Chargers

For most domestic single phase installations with a 7kW charger, a cable size of 6mm² twin and earth is often suitable for short runs. However, if the distance between the consumer unit and the charger is longer, or if the cable is installed in insulation, a 10mm² cable may be required to ensure compliance. For three phase 22kW chargers, which are less common in homes but often found in commercial settings, armoured cables such as 10mm² or even 16mm² may be used depending on the circumstances.

These figures are only examples. The actual size chosen will depend on a full site survey and load calculation by a qualified electrician. It is not safe to assume that what works in one property will work in another, as variations in layout, existing electrical demand, and installation method can change the requirements significantly.

The Role of Load Management

Another consideration in cable sizing is the total demand of the property. Many homes already have high energy appliances such as electric ovens, showers, and heat pumps. Adding an EV charger can place a significant strain on the system. Load management systems are sometimes installed alongside chargers to regulate when and how much current the unit draws. While this can reduce the stress on the household supply, it does not replace the need for the correct cable size. The wiring still needs to be able to handle the charger at full capacity, even if smart controls limit use at certain times.

Safety and Certification

Every EV charger installation must be carried out by a competent electrician and must comply with Part P of the Building Regulations. The work is notifiable, meaning that either your installer must be registered with a competent person scheme or the local authority building control must be informed. On completion, you should receive a certificate confirming the work complies with BS7671. This paperwork is essential for insurance, property sales, and peace of mind.

The installer will also ensure that protective devices such as residual current devices (RCDs) are correctly fitted. These devices protect both the cable and the user in the event of a fault. Using the correct size of cable is part of this overall protective system, ensuring that the installation is both safe and durable.

Why You Should Not DIY EV Charger Cabling

It is important to highlight that cable sizing and EV charger installation should never be treated as a do-it-yourself task. The calculations require professional training and a deep understanding of the wiring regulations. Incorrectly sized cables can have serious consequences, not only for safety but also for the long term performance of your charging system. Attempting the work without the proper knowledge and certification is likely to invalidate insurance and may result in enforcement action from building control.

Long Term Considerations

When planning an EV charger installation, it is sensible to think about the future. Even if you currently own a vehicle that only requires a 3.6kW or 7kW charger, your next car may demand higher charging rates. Some homeowners choose to install slightly larger cables than are immediately necessary to allow for future upgrades. This can be more cost effective than replacing the cabling at a later date. Discussing your long term needs with the installer can help ensure you make the right choice now and avoid unnecessary expense later.

Final Thoughts

The size of cable for an EV charger depends on a number of factors including charger capacity, installation method, and cable run length. While many domestic 7kW chargers can operate on 6mm² cable, longer runs or challenging conditions often require 10mm² or larger. For three phase systems, even larger armoured cables are commonly used. Ultimately, only a qualified electrician can assess your property and determine the correct specification in line with BS7671. By ensuring the right cable is installed, you not only comply with UK regulations but also guarantee the safety, reliability, and longevity of your charging system.