EV Charging & Solar PV FAQ

Mode 2 uses a portable cable with in-cable control box connected to a standard domestic socket — limited to 2.3–3.7kW and intended for occasional use only. Mode 3 uses a dedicated wall-mounted EVSE with a Type 2 connector — 7–22kW for regular charging. Mode 4 is DC fast charging using CCS or CHAdeMO connectors — 50–350kW at commercial charging stations.

BS 7671 Section 722 requires at minimum a Type A RCD for Mode 3 AC charging. A Type B RCD is required only if the EVSE does not include built-in DC fault protection. Many modern chargers have an integrated DC leakage sensor (6mA DC detection), allowing a Type A RCD to be used externally. Always check the charger manufacturer’s requirements for the specific model.

Mode 2 charging from an existing 13A socket is possible but not recommended for regular use — domestic sockets are not rated for continuous high-current loads, risking overheating. BS 7671 and most EV manufacturers recommend a dedicated Mode 3 circuit with its own protective device, sized for continuous 32A duty. A professional installation ensures safety and optimal charging speed.

PV DC string cables must carry 1.25 × Isc (panel short-circuit current) continuously. Apply derating for elevated roof temperatures — near roof-mounted panels, ambient can exceed 60°C, requiring correction factors as low as 0.58 for PVC insulation. Use double-insulated UV-resistant cables rated for the string voltage. Keep voltage drop below 1–2% to minimise energy losses.

BS 7671 Section 712 requires PV installations to have appropriate earthing and bonding. For systems with a transformer between the PV array and utility supply, standard earthing applies. Transformerless inverters may inject DC fault current, requiring Type B RCD protection on the AC side. All exposed metalwork including mounting frames must be bonded. Lightning protection considerations apply to roof-mounted arrays.

Calculate available capacity by subtracting existing maximum demand from the supply rating. Each 7.4kW charger adds 32A per phase. For multiple chargers, apply diversity factors: 0.8 for 2–5 chargers, 0.6 for 6–10 chargers. A load management system can dynamically limit total EV charging demand to stay within supply limits. DNO notification is typically required above 3.68kW per phase.

Smart charging systems communicate between the EVSE and a central controller to manage total electrical demand. When multiple EVs charge simultaneously, the system distributes available capacity among connected vehicles, reducing individual charge rates to stay within the supply limit. Advanced systems integrate with building energy management, tariff scheduling, and solar PV generation to optimise charging cost and reduce peak demand.

Export metering requirements depend on the local utility and feed-in tariff scheme. Some schemes pay for metered exports, requiring a bi-directional meter or separate export meter. Others use deemed (estimated) export at 50% of generation. Grid connection applications above certain thresholds (typically 3.68kW per phase) require DNO approval and may require G98/G99 compliance testing.

PV DC circuits have unique protection challenges because panels generate current continuously in daylight and cannot be switched off. String fuses protect against reverse current flow in parallel strings. DC isolators provide safe disconnection for maintenance. Surge protection devices guard against lightning-induced transients. Arc fault detection on the DC side prevents fire from series arc faults in connectors or damaged cables.