EV Charger Calculator
Cable sizing and circuit requirements for EV charger installations
Reference Info & Formulas
3.6kW: Slow, 10-12 hrs
7kW: Fast, 4-6 hrs
22kW: Rapid 3-phase, 1-2 hrs
Times for typical 60kWh battery
Section 722: EV charging
Type A RCD: Required
VD limit: 3%
IET Code of Practice for EV Charging
Data: BS 7671:2018+A2:2022 — Section 722, IET Code of Practice for EV
For guidance only. The responsibility for any electrical installation lies with the qualified person carrying out the work. Always verify calculations independently and apply professional judgement.
How This Calculator Works
EV charger circuits are sized based on continuous load rating with no diversity applied — the cable must handle 100% of the charger's rated current.
EV chargers are treated as continuous loads because a charging session can run for several hours at full rated current. A 7kW single-phase charger draws 32A (7000 / 230), and a 22kW three-phase unit draws 32A per phase (22000 / (√3 × 400)). BS 7671 Section 722 and the IET Code of Practice for Electric Vehicle Charging Equipment Installation govern the specific requirements for these circuits.
The calculator selects the cable size from Table 4D5 based on the installation method, applies correction factors for ambient temperature, grouping, and thermal insulation, then verifies voltage drop is within acceptable limits. For outdoor cable runs to detached garages or driveways, SWA (steel wire armoured) cable is typically required, with current ratings taken from Table 4D4A.
RCD Protection Requirements
Quick Reference — EV Charger Circuit Sizing
Common EV charger ratings and cable requirements
BS 7671 Section 722, Table 4D5| Charger Rating | Current Draw | Cable Size (Method C) | MCB Rating |
|---|---|---|---|
| 3.6kW (16A single-phase) | 16A | 2.5mm² | 20A |
| 7.4kW (32A single-phase) | 32A | 6mm² | 32A |
| 11kW (16A three-phase) | 16A per phase | 2.5mm² | 20A per phase |
| 22kW (32A three-phase) | 32A per phase | 6mm² | 32A per phase |
Based on Method C (clipped direct), 30°C ambient, no thermal insulation contact. Verify voltage drop for runs exceeding 20m.
Practical Notes
PME Earthing Restrictions
Design Voltage Drop for 2-3%
No Diversity in Maximum Demand
Frequently Asked Questions
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