Before the Cable Goes In: Due Diligence for a Domestic EV Charge Point
Photo: Julian Herzog (Website), CC BY 4.0, via Wikimedia Commons
A home charge point looks like a modest addition: a small wall-mounted box, a length of cable, an hour or two of work. In electrical terms it is anything but modest. A typical 7.4 kW domestic charger draws around 32 amps continuously for hours at a time, which is a far more demanding duty than almost anything else in a house. Before anyone drills a hole in the wall, five things need to be settled.
Start with the supply, not the charger
The first question is not which model to buy but whether the existing supply can carry it. A proper load assessment considers the rating of the incoming cut-out fuse, the capacity of the consumer unit, the cross-sectional area and routing of the proposed cable, and the existing demand of the property — heating, cooking, showers, outbuildings. Diversity assumptions that were generous for a house with a gas hob look very different in a property with an electric range, an immersion heater and a heat pump.
Where headroom is limited, the answer is not to install a smaller cable and hope. It is either a supply upgrade, agreed with the distribution network operator, or a charge point with dynamic load management that continuously monitors the incoming supply and reduces charging current when the house needs it. Both are legitimate solutions. Neither is free, and neither appears in a quote that was assembled without a site survey.
Earthing and the PME question
Most UK homes are supplied with a protective multiple earthing, or PME, arrangement, where the neutral conductor also performs an earth function. It is safe for ordinary domestic installations, but it introduces a specific risk for vehicle charging: if the combined neutral-earth conductor is damaged or lost, the metalwork of a connected vehicle can rise to a dangerous potential while a person is touching it.
BS 7671 addresses this directly. A charge point on a PME supply must incorporate open-circuit PEN fault detection, or the installation must use a suitable alternative earthing arrangement — commonly a dedicated earth electrode providing a TT system for the charging point, or separation via a transformer. Your installer should be able to explain, in plain terms, which of these applies to your property and why. If the answer is vague, that is your answer.
RCD protection that suits the load
Electric vehicle charging can produce smooth direct current leakage. Above roughly 6 mA of DC residual current, a conventional Type A residual current device may not trip reliably, because the DC component can saturate its sensing circuit. The regulations therefore require either a Type B RCD, or a Type A device backed by a residual direct current detecting device — which in practice is built into most modern charge points.
Ask what protective arrangement is being provided and where it sits. A charge point with integral 6 mA DC detection and a Type A RCD upstream is a common and compliant design. What is not acceptable is a Type A device alone, with no DC detection anywhere in the circuit. It is a detail that is easy to overlook on a specification sheet and expensive to discover later.
Tell the network operator
Charge points are not invisible to the grid. For most single-phase installations above 3.6 kW, and certainly for three-phase and multi-unit installations, the installer must notify the distribution network operator before commissioning, and in some cases obtain approval first. This is not bureaucracy for its own sake: a cluster of chargers on a street can affect the local low-voltage network, and the DNO needs visibility of new load.
Notification is normally handled by the installer, and it should be confirmed in writing rather than assumed. If a quotation makes no reference to it, ask directly who is submitting the application and when. An un-notified installation can complicate a future supply upgrade, a house sale or an insurance claim.
Certification, notification and the paper trail
In England and Wales, the installation of a new circuit for a charge point is notifiable work under Part P of the Building Regulations. It must either be certified through a competent person scheme or notified to building control in advance. Scotland and Northern Ireland have their own regimes, with different procedural requirements. In every case, the work should conclude with the correct certificate, test results and, where applicable, notification to the local authority.
Alongside the electrical paperwork, ask for confirmation that the unit meets the smart charge point requirements, that the manufacturer's warranty has been registered, and that the installer holds appropriate public liability and professional indemnity cover. A five-line invoice is not a commissioning record.
Why the cheapest quote costs the most
The economy in a low quotation is rarely in labour efficiency. It is usually in the omissions: no load calculation, no PEN fault protection, a Type A device standing alone, no DNO notification, an undersized cable on a long run, no certificate. Each omission is invisible on completion day and each one has a way of surfacing at the worst possible moment — during a survey, an insurance assessment, or a fault investigation.
A charge point is a fixed asset with a service life measured in a decade or more. The sensible comparison is not between two headline prices but between two specifications. Ask each contractor to state, in writing, their load calculation, their earthing solution, their protective device arrangement, their notification route and the certification they will issue. The quotation that answers all five clearly is the one worth having, even when it is not the shortest.
