EV Charger Cable Size Guide
A 7 kW charger is a sustained load, so the cable must be selected from the supply, route and protective measures as a complete circuit design.
EV cable sizing begins with the charge-point rating and available supply capacity, then accounts for installation method, ambient temperature, grouping, voltage drop and the selected protective device. The longest driveway run is often the deciding factor.
This is practical guidance for competent electricians. Assess the actual installation, follow the current edition of BS 7671 and manufacturer instructions, and stop where the work cannot be completed safely.
Key takeaways
- Agree the scope and make the installation safe before starting work.
- Use a controlled sequence rather than relying on a single reading or visual assumption.
- Record the actual result, limitation or action taken while it is still traceable.
- Check the result against the design, protective measures and equipment instructions.
- Issue the appropriate certificate or report when the work is complete.
Scope the work first
EV cable sizing begins with the charge-point rating and available supply capacity, then accounts for installation method, ambient temperature, grouping, voltage drop and the selected protective device. The longest driveway run is often the deciding factor.
Method
Survey the supply and proposed route, establish design current and diversity/load-management approach, apply correction factors, check voltage drop and verify the protective-device and disconnection arrangement. Follow the charge-point manufacturer's instructions.
Doing this on a job? Cable sizing calculator — part of TradePlanr. Free to start, no card needed.
Checks and common pitfalls
Do not select a cable only from a typical 7 kW installation. Thermal insulation, buried sections, grouping, long runs, PME arrangements and equipment-specific RCD/DC protection can materially change the design.
Record and hand over
Keep the calculation, cable route, device details, test results and commissioning information with the EV certificate. Explain any load-management settings and supply limitations to the client.
Keep the evidence with the job
Record readings, limitations and remedial actions as you work. A clear certificate or report protects the client and makes the next visit easier to manage.
From guidance to action
Frequently asked questions
Is there one standard cable size for a 7 kW charger?
No. A 7 kW charger has a common design current, but cable size depends on route length, installation method, correction factors, voltage drop and protective arrangements.
Can I rely on a standard rule of thumb?
No. The installation method, supply characteristics, equipment instructions and the current requirements all affect the correct decision. Use the guide as a workflow, then assess the actual job.
What should be recorded?
Record the scope, results, limitations, observations, remedial work and the certificate or report appropriate to the work carried out.
Related guides
EV Charger Installation: A Practical Guide
Surveying, cable sizing, earthing and certifying a domestic EV charge point installation.
Open PEN Protection for EV Charging
Understand the open-PEN risk on PME supplies and assess the protective solution required for an EV charging installation.
Cable Reference Methods Explained
How cable installation reference methods affect current-carrying capacity, correction factors and final cable selection.
