Domestic EV charge point installation

Supply and earthing survey

The IET Code of Practice treats the site survey as a formal stage, not a look round. Record the findings and keep them with the job file.

• Earthing arrangement — TN-S, TN-C-S (PME), or TT. Confirm it by inspection at the cut-out and by measurement (Ze), not by assumption.
• Supply characteristics — single or three phase, nominal voltage, supplier's cut-out fuse rating (60 A, 80 A, 100 A), and prospective fault current (Ipf) at the origin.
• Measured Ze and Ipf recorded before design decisions are made — the disconnection times and device breaking capacity both depend on them.
• Existing maximum demand assessed with diversity to BS 7671 Reg 311.1, using the On-Site Guide Appendix A factors, and compared against the cut-out fuse.
• Condition of the existing installation — consumer unit type, RCD provision, main protective bonding sizes (normally 10 mm² on PME), main earthing conductor (16 mm² typical on PME), and whether an EICR-style sample is needed before adding load.
• Consumer unit spare ways, busbar rating, and whether a separate garage/outbuilding board or a dedicated enclosure alongside the main board is the better answer.
• Whether the property is a flat, maisonette, or has a shared supply/riser — these are handled as small commercial jobs, not simple domestic ones.

Site and vehicle survey

• Charge point location — off-street parking, cable reach to the vehicle inlet on both sides of the car, and no cable trailing across a public footway (crossing a footway is not acceptable).
• Mounting height — tethered and untethered units sited so the connector and cable are clear of the ground; the CoP recommends a socket/connector height typically 0.75 m to 1.2 m, and always within the manufacturer's range.
• Vehicle connector type — Type 2 socket or tethered lead; Mode 3 charging for AC, Mode 2 (granny lead) treated as an occasional-use item only, not an installation.
• IP and IK rating suitable for external mounting, plus protection from vehicle impact (bollard, kerb, or mounting position).
• Cable route — measured, not estimated. Wall surfaces, cavity or solid construction, clipped direct, in conduit/trunking, or buried; note any structural or fire-stopping penetrations.
• Where any part is buried, depth and protection to Section 522 — armoured cable or cable in conduit with marker tape, minimum 500 mm under ground (600 mm under a driveway).
• Wi-Fi / mobile signal strength at the unit — the Smart Charge Point Regulations require connectivity for the smart functions, and a unit that cannot see the network is a callback.
• Whether solar PV, a battery, or a heat pump is installed or planned — this changes both load management and the export/solar-diverting features selected.

PME and open-PEN — the decision that defines the job

Regulation 722.411.4.1 prohibits connecting the vehicle's exposed-conductive-part to a PME earth unless one of the permitted measures is applied. This is the single most common design failure on domestic EV work.

• Option 1 — TT island (earth electrode) for the charge point, with the electrode kept clear of the PME earthed metalwork (the CoP advises separation, typically 2 m or more where achievable), and the charging circuit protected by a 30 mA RCD suitable for the TT arrangement. Measure Ra and confirm disconnection.
• Option 2 — a device or charge point with integral open-PEN (PEN fault) detection that disconnects all live conductors including the protective conductor within the required time. Most modern units use this; confirm it on the datasheet, not the marketing page.
• Option 3 — the 'not simultaneously accessible' route of 722.411.4.1(i), which is rarely satisfiable in practice on a domestic driveway and should not be relied on.
• On TN-S or TT supplies, open-PEN protection is not required — but still confirm the earthing arrangement by measurement, because a 'TN-S' cut-out is frequently a converted PME.
• Where a TT island is used, a warning label and clear documentation must be provided so future work does not bond the two systems together.
• Open-PEN devices work on voltage-threshold detection; they need a good neutral reference, and their operating limits must be checked against the actual supply.

Protection, RCDs and circuit design

• Dedicated final circuit per Reg 722.55.101 — one charge point per circuit, no shared loads, its own overcurrent protective device at the board.
• 30 mA RCD protection for each connection point (722.531.3.101), disconnecting all live conductors.
• DC fault current management — either a Type B RCD, or a Type A RCD combined with equipment providing DC fault detection at 6 mA or above (most compliant chargers include this internally; the datasheet must state it).
• Do not rely on an upstream RCD shared with other circuits — nuisance tripping on a 7 kW load will take out the rest of the installation.
• Overcurrent device rated for the continuous load — a 7.4 kW single-phase unit draws 32 A continuously; select the device and cable for continuous duty, not intermittent.
• Check breaking capacity against the measured Ipf, and check Zs against the maximum values for the device and disconnection time (0.4 s for a 230 V final circuit).
• Surge protection — where the installation requires SPD provision under Section 443/534, the charge point circuit is covered by the SPD at the origin; an external unit on a long buried run may warrant additional protection.
• AFDDs are not mandated for EV circuits in domestic premises, but the risk assessment route of 421.1.7 should be considered where the run is long or concealed.
• Isolation — a means of isolation local to the charge point is strongly recommended by the CoP, particularly where the board is remote from the unit.

Cable selection and installation

• Size for continuous current, not diversified load: a 32 A charge point is a 32 A continuous circuit.
• Typical domestic runs use 6 mm² twin & earth internally, or 6 mm² / 10 mm² SWA externally and buried — but the size must be calculated, never assumed.
• Apply every correction factor that applies: ambient temperature (Ca), grouping (Cg), thermal insulation (Ci), and the BS 3036 factor where relevant.
• Voltage drop limited to 5% overall (3% lighting / 5% power guidance); long driveway runs frequently push 6 mm² beyond limit and need 10 mm².
• Verify the adiabatic equation for the CPC, especially where a reduced CPC in twin & earth is used with a high Ipf.
• SWA terminations correctly glanded with the armour used as CPC only where its cross-sectional area is verified as adequate; otherwise run a separate CPC.
• Buried cable: 500 mm minimum depth in soft ground, 600 mm under driveways, marker tape above, and mechanical protection where it rises.
• Support, fire-resistant fixings on escape routes, correct bend radii, and proper sealing of external entries to maintain the IP rating.

Smart charging, load management and grants

• The Electric Vehicles (Smart Charge Points) Regulations 2021 apply to every new domestic and workplace charge point in Great Britain — smart functionality, default off-peak charging windows, randomised delay up to 10 minutes, and security/tamper requirements.
• A statement of compliance must be supplied with the unit; keep a copy with the job file.
• Where maximum demand assessment shows the supply is marginal, apply load management: a CT clamp on the tails, dynamic load balancing, or a supply-limiting device that curtails charging rather than tripping the cut-out.
• Do not simply uprate the assumption — either the demand calculation supports the load, load management limits it, or the DNO supply is upgraded.
• DNO notification — connections under 32 A single phase are generally notified after the event under ENA G98/G99-style arrangements for generation; for EV load, notify the DNO in line with their current requirements and always where load management is not fitted or the supply is marginal.
• Above 60 A — once the assessed maximum demand has been calculated with the new charge point included, and the result exceeds 60 A, the DNO must be informed before the installation proceeds to ensure compliance with their connection arrangements. This applies whether the demand is met outright or a load-limiting (load curtailment) scheme is proposed — limiting the charger to keep demand within the supply must be agreed with the DNO under an ENA G100 arrangement, not fitted unilaterally.
• Where the DNO is informed, record the outcome in the job file — an approved connection, a G100 load-limiting agreement, or a supply upgrade offer — as this evidence forms part of the maximum demand assessment required by Reg 311.1.
• Grant work (OZEV / EV chargepoint grant for flats and renters, and the workplace scheme) requires an authorised installer and an approved charge point model — check both before quoting.
• Solar integration — where a solar diverter or matching charge mode is used, confirm the CT positions and that export limits and G98/G99 conditions are still met.

Inspection, testing and certification

• Test the circuit as a new circuit: continuity of protective conductors (R1+R2), continuity of ring where relevant, insulation resistance (500 V d.c., ≥1 MΩ, isolating electronics in the charge point first), polarity, Ze, Zs, and Ipf.
• RCD testing at the charge point connection — operating times at IΔn and 5IΔn, plus the manufacturer's test-button check. For Type B or DC-capable devices, test with an instrument capable of the correct waveform.
• Where a TT island is used, measure and record Ra and confirm disconnection times are met.
• Verify the open-PEN device function by the manufacturer's method — do not simulate PEN faults improvised on site.
• Functional test with the actual vehicle or an EVSE simulator: charge start/stop, correct current delivery, pilot signal (CP), proximity (PP), lock function on tethered/socket units, and load-management curtailment.
• Issue an Electrical Installation Certificate for the new circuit (a Minor Works Certificate is not appropriate for a new circuit).
• Building Regulations Part P notification through the Competent Person Scheme — EV charge point work in a dwelling is notifiable.
• Label the charge point circuit at the board, update the schedule, and fit any required TT/open-PEN warning notices.
• Hand over: user instructions, app setup, statement of compliance, EIC, and the recommended inspection interval — the CoP suggests periodic inspection of the charging equipment and circuit, typically at intervals no longer than 3 years for domestic use or as advised by the manufacturer.

Common failures to avoid

• Assuming TN-S from the look of the cut-out instead of measuring and confirming PME.
• Fitting a charge point on a spare way behind a shared 30 mA RCD.
• Using a Type AC RCD — never acceptable for EV charging.
• Sizing 6 mm² for a 40 m buried run and failing voltage drop.
• No maximum demand assessment, no load management, and a 60 A cut-out.
• Cable buried at spade depth with no marker tape or mechanical protection.
• Issuing a Minor Works Certificate for what is a brand-new circuit.
• No Part P notification, leaving the homeowner without compliance paperwork at sale.