EV Charger Load Assessment
Complete the electrical load assessment for EV charger installation \u2014 supply check, cable sizing, and earthing requirements
Reference Info & Formulas
3.6kW (16A): Slow charge, 10-12 hrs
7kW (32A): Fast, most common domestic
22kW (32A 3ph): Rapid, commercial
7kW is standard for UK home installations
Earth electrode REQUIRED for EV chargers on TN-C-S (PME) supplies
Per Regulation 722.411.4.1
Unless charger has PEN fault detection
Data: BS 7671:2018+A2:2022 Section 722, IET Code of Practice for EV Charging
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
The EV load assessment calculator checks supply adequacy, applies diversity for multiple chargers, and determines cable, protection, and earthing requirements.
The assessment follows the process outlined in the IET Code of Practice for Electric Vehicle Charging Equipment Installation. It starts with the existing maximum demand (measured or estimated), adds the EV charger demand with appropriate diversity factors, and checks whether the total falls within the main fuse rating. If load management is specified, the effective demand is reduced accordingly.
Total demand = Existing demand + (N x I_charger x Diversity factor)- Existing demand
- = Current maximum demand in amps (measured or estimated)
- N
- = Number of EV chargers
- I_charger
- = Current rating of each charger (A)
- Diversity factor
- = 1.0 for 1 charger, 0.8 for 2, 0.7 for 3, 0.6 for 4+
IET Code of Practice for EV Charging, Table A.1
The cable is sized for the individual charger circuit (no diversity on a single final circuit) using BS 7671 tables, with a voltage drop check against the 3% limit for final circuits. Protection is selected per Section 722, and the earthing assessment checks whether an earth electrode is required based on the supply type.
Quick Reference \u2014 EV Charger Circuit Sizing
Common EV charger ratings and requirements
BS 7671 Section 722, Tables 4D5 and 4D4A| Charger | Current | Cable (Clipped) | Cable (SWA Buried) | MCB | RCD |
|---|---|---|---|---|---|
| 3.6kW (1ph) | 16A | 2.5mm² T&E | 2.5mm² SWA | 20A Type B | Type A 30mA |
| 7kW (1ph) | 32A | 6mm² T&E | 6mm² SWA | 32A Type B | Type A 30mA |
| 7.4kW (1ph) | 32A | 6mm² T&E | 6mm² SWA | 32A Type B | Type A 30mA |
| 11kW (3ph) | 16A/phase | 2.5mm² T&E | 2.5mm² SWA | 20A Type B | Type B 30mA |
| 22kW (3ph) | 32A/phase | 6mm² T&E | 6mm² SWA | 32A Type B | Type B 30mA |
Cable sizes assume Method C or Method D, 30\u00B0C ambient, no grouping. Verify voltage drop for runs exceeding 20m. RCD type depends on charger DC fault detection capability.
Practical Notes
PME Earthing \u2014 Regulation 722.411.4.1
Supply Adequacy \u2014 Measure, Don't Guess
Dynamic Load Management Saves Supply Upgrades
Frequently Asked Questions
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