Commercial EV Fleet Charging: Diversity & Dynamic Load Balancing (DLM)

Installing multiple EV charge points across a commercial car park or commercial van fleet rapidly exceeds the available supply capacity of the building. Under BS 7671, EV charging loads cannot take standard diversity factors without automated dynamic load curtailment.

The Diversity Dilemma (Regulation 722.311)

In standard domestic and commercial calculations, diversity factors (IET On-Site Guide Table A1) allow sizing sub-mains below the sum of connected loads. However, EV chargers are continuous 100% duty loads.

• A single 22 kW three-phase charger draws 32 A per phase continuously.
• Ten 22 kW chargers connected simultaneously represent a 320 A per phase load.
• Without active management, connecting this fleet would require a six-figure DNO substation transformer upgrade.

Dynamic Load Management (DLM) Architectures

Regulation 722.311.201 explicitly permits applying diversity where an Automated Load Management System (ALMS) is installed:

1. Static Load Balancing (Fixed Ceiling)

A dedicated sub-main with a fixed capacity (e.g. 100 A) is shared between chargers. When 2 cars plug in, each receives 32 A; when 5 cars plug in, power is throttled down to 20 A each.

2. Dynamic Real-Time Load Balancing (CT Clamp Monitoring)

Current transformers (CTs) monitor the total building incoming power at the main supply cut-out in real time. The DLM controller calculates the spare headroom (Available Capacity = Maximum Import Capacity − Building Base Load) and allocates power dynamically:

• Daytime (High building demand): Charger output throttles down to prevent blowing main incoming DNO fuses.
• Night (Low building demand): Full capacity is released to charge the fleet at maximum speed.

OCPP & Cloud vs Local Hardware Controllers