Deploying commercial multi-point EV charging infrastructure into existing buildings inevitably collides with physical grid capacity. Under BS 7671 Regulation 722.311, EV charging demand is calculated assuming zero diversity. Without automated management, even four 22 kW chargers (draw of 128 A per phase) can overload a building's main switchboard. Here is the technical design architecture for Dynamic Load Balancing (DLB) under Regulation 722.311.201, OCPP 1.6J/2.0.1, and ENA requirements.
The Zero-Diversity Mandate vs Dynamic Load Management
In general electrical installation design, diversity factors allow circuits to be sized for less than their maximum simultaneous load. However, Regulation 722.311 establishes an uncompromising rule:
BS 7671 Regulation 722.311:
"It shall be assumed that in normal use, each charging point will be used at its rated current, unless dynamic load control is provided."
In commercial fleet depots, workplace car parks, or residential apartment blocks, applying zero diversity means multiplying total charger capacity by 100%. A bank of ten 22 kW three-phase chargers demands 319 A per phase, requiring costly substation transformer upgrades from the Distribution Network Operator (DNO).
Regulation 722.311.201 formally permits diversity to be applied when an automated control system monitors total installation current and dynamically adjusts charging rates to prevent supply overloads.
System Architecture: The Three Control Layers
- Grid Import Monitoring (Intake CT Clamps): Class 1 or Class 0.5 Current Transformers (CTs) or an MID-approved multi-function energy meter monitor active current across all three phases at the main incoming supply cut-out.
- Central Load Controller (Master Controller): A local edge gateway (or primary master charger) receives real-time current measurements via Modbus RTU (RS485) or Modbus TCP (Ethernet) at sampling intervals ≤ 1 second.
- Charge Point Actuation (OCPP Profiles): The controller allocates available capacity to connected vehicles using OCPP 1.6J (Open Charge Point Protocol) or OCPP 2.0.1 smart charging profiles (specifically
TxDefaultProfileandTxProfile).
| Building Load Condition | Intake Current (per phase) | Available EV Capacity | Per-Charger Allocation (4x 22 kW Units) |
|---|---|---|---|
| Base Load (Night / Off-Peak) | 40 A / 200 A Capacity | 160 A available | 32 A per charger (Full 22 kW) |
| Peak Building Demand (Afternoon) | 150 A / 200 A Capacity | 50 A available | 12.5 A per charger (≈ 8.6 kW) |
| Extreme Demand (Chillers + Kitchens) | 185 A / 200 A Capacity | 15 A available | Paused or throttled to minimum 6 A |
The Mandatory 5-Second Fail-Safe Mechanism
The integrity of a DLB system protects upstream DNO service fuses and commercial switchboards from thermal destruction. Communication networks (Wi-Fi, Ethernet, or RS485) can and will fail.
Mandatory DLB Fail-Safe Protocol:
Under DNO connection agreements and safety standards, if communication between the intake meter and the charge point controller is lost:
- The charge point must detect the heartbeat loss and initiate curtailment within < 5 seconds.
- Each charger must automatically drop its charging current to a pre-configured safe fallback level, typically 6 A (minimum IEC 61851-1 pilot current) or 0 A (complete charging suspension).
- Never rely on cloud-only DLB algorithms for fuse protection. Latency and internet dropouts will cause DNO supply fuse rupture before cloud servers respond!
Phase Balancing on Single-Phase EV Fleets
When multiple single-phase vehicles connect to a three-phase charging system, severe phase unbalance can occur, overheating the distribution neutral conductor and tripping the supply. Modern commercial DLB controllers monitor individual phase currents and rotate charging authorizations across phases to maintain phase balance within ±10% across the supply.